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1.  Hair-cycle dependent differential expression of ADAM 10 and ADAM 12 
Dermato-endocrinology  2009;1(1):46-53.
Background
ADAM proteases play important roles in processes of development and differentiation. However, no report has been found in the literature addressing the expression and function of ADAM proteases during hair cycling.
Results
Cytoplasmic expression pattern of ADAM 10, 12 was similar between normal epidermis and hair infundibulum. In addition, cytoplasmic expression of ADAM 10 was observed in the hair bulb keratinocytes and fibroblasts of dermal papilla in anagen I–III hair follicles. In contrast, decreased ADAM 10 expression was observed in the hair matrix keratinocytes as compared to the hair bulb keratinocytes in anagen I–III hair follicles. Interestingly, ADAM 10 immunoreactivity was expressed weakly in the lower portion of outer root sheath (ORS) of anagen VI hair follicles, and strong ADAM 10 expression was detected in the ORS of catagen and telogen hair follicles. By contrast, ADAM 12 expression was not detected in the hair bulb keratinocytes of anagen I–III hair follicles. ADAM 12 immunoreactivity firstly appeared in the inner root sheath ( IRS ) of anagen IV—V hair follicles and was down-regulated in the IRS and hair cortex and medulla of catagen hair follicles, Strong ADAM 12 immunoreactivity was observed in the ORS of catagen and telogen hair follicles.
Material and methods
Samples of normal human skin (n = 30) were used. Immunohistochemical analysis was performed using ADAM 10, 12 specific polyclonal antibodies and a sensitive streptavidin-peroxidase technique.
Conclusion
Our study demonstrates a comparable staining pattern of decreased ADAM 10 immunoreactivity in hair matrix keratinocytes and the basal cell layer of normal epidermis and hair infundibulum. Expression of ADAM 10 in dermal papilla cells may imply a role in the induction and development of anagen hair follicles. In addition, expression of ADAM 10 in the ORS and hair bulb assume the involvment of ADAM 10 in the downward migration of anagen hair follicles. Furthermore ADAM 12 expression in the IRS may indicate a role in the differentiation of anagen hair follicles. Downregulation of ADAM 12 upon the onset of catagen hair stage suggests that ADAM 12 may play an important role of ADAM 12 in the apoptosis of hair follicle keratinocytes. In summary our findings suggest that ADAM 10 and 12 may be of importance for the regulation of hair cycling.
PMCID: PMC2715197  PMID: 20046589
ADAM 10; ADAM 12; hair cycle; immunohistochemistry; hair follicle
2.  Expression Of Nucleosomal Protein HMGN1 In The Cycling Mouse Hair Follicle 
Gene expression patterns : GEP  2009;9(5):289-295.
Here we examine the expression pattern of HMGN1, a nucleosome binding protein that affects chromatin structure and activity, in the hair follicle and test whether loss of HMGN1 affects the development or cycling of the follicle. We find that at the onset of hair follicle development, HMGN1 protein is expressed in the epidermal placode and in aggregated dermal fibroblasts. In the adult hair follicle, HMGN1 is specifically expressed in the basal layer of epidermis, in the outer root sheath, in the hair bulb, but not in the inner root sheath and hair shaft. The expression pattern of HMGN1 is very similar to p63, suggesting a role for HMGN1 in the transiently amplifying cells. We also find HMGN1 expression in some, but not all hair follicle stem cells as detected by its colocalization with Nestin and with BrdU label-retaining cells. The appearance of the skin and hair follicle of Hmgn1-/- mice was indistinguishable from that of their Hmgn1+/+ littermates. We found that in the hair follicle the expression of HMGN2 is very similar to HMGN1 suggesting functional redundancy between these closely related HMGN variants.
doi:10.1016/j.gep.2009.03.002
PMCID: PMC2738608  PMID: 19303948
chromatin; HMGN; p63; hair follicle
3.  Steady and Temporary Expressions of Smooth Muscle Actin in Hair, Vibrissa, Arrector Pili Muscle, and Other Hair Appendages of Developing Rats 
Acta Histochemica et Cytochemica  2011;44(3):141-153.
The hair erection muscle, arrector pili, is a kind of smooth muscle located in the mammalian dermis. The immunohistochemical study using an antibody against smooth muscle alpha actin (SMA) showed that the arrector pili muscle develops approximately 1–2 weeks after birth in dorsal and ventral skin, but thereafter they degenerate. The arrector pili muscle was not detected in the mystacial pad during any stage of development, even in the neighboring pelage-type hair follicle. A strong signal of SMA in the skin was located in the dermal sheath as well as in some outer root sheath cells in the hair and vibrissal follicles. Positive areas in the dermal and outer root sheaths were restricted to a lower moiety, particularly areas of similar height, where keratinization of the hair shaft occurs. This rule is valid for both pelage hair follicles and vibrissal follicles. At medium heights of the follicle, SMA staining in the dermal sheath was patchy and distant from the boundary between dermis and epidermis. In contrast to SMA, vimentin was expressed over the entire height of the dermal sheath. Unlike the arrector pili muscle, the expression of SMA in the dermal sheath was observed during fetal, neonatal, and adult stages. The presence of actin-myosin and vimentin fibers in supporting cells is thought to be beneficial for the hair follicle to cope with the movement of the hair shaft, which may be caused by physical contacts with outside materials or by the contraction of internal muscles.
doi:10.1267/ahc.11013
PMCID: PMC3130146  PMID: 21753860
hair; arrector pili muscle; smooth muscle actin; vimentin; dermal sheath
4.  Co-factors of LIM domains (Clims/Ldb/Nli) regulate corneal homeostasis and maintenance of hair follicle stem cells 
Developmental biology  2007;312(2):484-500.
The homeostasis of both cornea and hair follicles depends on a constant supply of progeny cells produced by populations of keratin (K) 14-expressing stem cells localized in specific niches. To investigate the potential role of Co-factors of LIM domains (Clims) in epithelial tissues, we generated transgenic mice expressing a dominant-negative Clim molecule (DN-Clim) under the control of the K14 promoter. As expected, the K14 promoter directed high level expression of the transgene to the basal cells of cornea and epidermis, as well as the outer root sheath of hair follicles. In corneal epithelium, the transgene expression causes decreased expression of adhesion molecule BP180 and defective hemidesmosomes, leading to detachment of corneal epithelium from the underlying stroma, which in turn causes blisters, wounds and an inflammatory response. After a period of epithelial thinning, the corneal epithelium undergoes differentiation to an epidermis-like structure. The K14-DN-Clim mice also develop progressive hair loss due to dysfunctional hair follicles that fail to generate hair shafts. The number of hair follicle stem cells is decreased by at least 60% in K14-DN-Clim mice, indicating that Clims are required for hair follicle stem cell maintenance. In addition, Clim2 interacts with Lhx2 in vivo, suggesting that Clim2 is an essential co-factor for the LIM homeodomain factor Lhx2, which was previously shown to play a role in hair follicle stem cell maintenance. Together, these data indicate that Clim proteins play important roles in the homeostasis of corneal epithelium and hair follicles.
doi:10.1016/j.ydbio.2007.09.052
PMCID: PMC2494569  PMID: 17991461
LIM domain transcription factors; Co-factors of LIM domains; Clim; Lhx2; hair follicle stem cells; cornea; adhesion; hemidesmosomes; BP180
5.  Nitric Oxide Functions as a Positive Regulator of Root Hair Development 
Plant Signaling & Behavior  2006;1(1):28-33.
The root epidermis is composed of two cell types: trichoblasts (or hair cells) and atrichoblasts (or non-hair cells). In lettuce (Lactuca sativa cv. Grand Rapids var. Rapidmor oscura) plants grown hydroponically in water, the root epidermis did not form root hairs. The addition of 10 µM sodium nitroprusside (SNP), a nitric oxide (NO) donor, resulted in almost all rhizodermal cells differentiated into root hairs. Treatment with the synthetic auxin 1-naphthyl acetic acid (NAA) displayed a significant increase of root hair formation (RHF) that was prevented by the specific NO scavenger carboxy-PTIO (cPTIO). In Arabidopsis, two mutants have been shown to be defective in NO production and to display altered phenotypes in which NO is implicated. Arabidopsis nos1 has a mutation in an NO synthase structural gene (NOS1), and the nia1 nia2 double mutant is null for nitrate reductase (NR) activity. We observed that both mutants were affected in their capacity of developing root hairs. Root hair elongation was significantly reduced in nos1 and nia1 nia2 mutants as well as in cPTIO-treated wild type plants. A correlation was found between endogenous NO level in roots detected by the fluorescent probe DAF-FM DA and RHF. In Arabidopsis, as well as in lettuce, cPTIO blocked the NAA-induced root hair elongation. Taken together, these results indicate that: (1) NO is a critical molecule in the process leading to RHF and (2) NO is involved in the auxin-signaling cascade leading to RHF.
PMCID: PMC2633697  PMID: 19521473
auxin; nitric oxide; root hair; lettuce; arabidopsis; nos1 mutant; nia1; nia2 mutant
6.  Conditional Activin Receptor Type IB (Acvr1b) Knockout Mice Reveal Hair Loss Abnormality 
The in vivo functions of the activin A receptor type 1b (Acvr1b) have been difficult to study because Acvr1b−/− mice die during embryogenesis. To investigate the roles of Acvr1b in the epithelial tissues, we created mice with a conditional disruption of Acvr1b (Acvr1bflox/flox) and crossed them with K14-Cre mice. Acvr1bflox/flox; K14-Cre mice displayed various degrees of hairlessness at postnatal day 5, and the phenotype is exacerbated by age. Histological analyses showed that those hair follicles that developed during morphogenesis were later disrupted by delays in hair cycle reentry. Failure in cycling of the hair follicles and regrowth of the hair shaft and the inner root sheath resulted in subsequent severe hair loss. Apart from previous reports of other members of the transforming growth factor-β/activin/bone morphogenic protein pathways, we demonstrate a specialized role for Acvr1b in hair cycling in addition to hair follicle development. Acvr1bflox/flox; K14-Cre mice also had a thicker epidermis than did wild-type mice, which resulted from persistent proliferation of skin epithelial cells; however, no tumor formation was observed by 18 months of age. Our analysis of this Acvr1b knockout mouse line provides direct genetic evidence that Acvr1b signaling is required for both hair follicle development and cycling.
doi:10.1038/jid.2010.400
PMCID: PMC4049458  PMID: 21191412
7.  The miRNA-Processing Enzyme Dicer Is Essential for the Morphogenesis and Maintenance of Hair Follicles 
Current biology : CB  2006;16(10):1041-1049.
Summary
The discovery that microRNAs (miRNAs) play important roles in regulating gene expression via post-transcriptional repression has revealed a previously unsuspected mechanism controlling development and progenitor-cell function (reviewed in [1, 2]); however, little is known of miRNA functions in mammalian organogenesis. Processing of miRNAs and their assembly into the RNA-induced silencing (RISC) complex requires the essential multifunctional enzyme Dicer [1]. We found that Dicer mRNA and multiple miRNAs are expressed in mouse skin, suggesting roles in skin- and hair-follicle biology. In newborn mice carrying an epidermal-specific Dicer deletion, hair follicles were stunted and hypoproliferative. Hair-shaft and inner-root-sheath differentiation was initiated, but the mutant hair follicles were misoriented and expression of the key signaling molecules Shh and Notch1 was lost by postnatal day 7. At this stage, hair-follicle dermal papillae were observed to evaginate, forming highly unusual structures within the basal epidermis. Normal hair shafts were not produced in the Dicer mutant, and the follicles lacked stem cell markers and degenerated. In contrast to decreased follicular proliferation, the epidermis became hyperproliferative. These results reveal critical roles for Dicer in the skin and implicate miRNAs in key aspects of epidermal and hair-follicle development and function.
doi:10.1016/j.cub.2006.04.005
PMCID: PMC2996092  PMID: 16682203
8.  Expression patterns of MITF during human cutaneous embryogenesis: evidence for bulge epithelial expression and persistence of dermal melanoblasts 
Journal of cutaneous pathology  2008;35(7):615-622.
Background
The mechanisms whereby melanocytes populate the epidermis and developing hair follicles during embryogenesis are incompletely understood. Recent evidence implicates an intermediate mesenchymal stage in this evolutionary process in which HMB-45-positive melanocyte precursors (`melanoblasts') exist both in intradermal as well as intraepithelial and intrafollicular compartments. The melanocyte master transcriptional regulator, microphthalmia transcription factor (MITF), identifies mature melanocytes as well as melanocyte precursor stem cells that reside in the bulge region of the hair follicle.
Methods
To better define the use of MITF expression in the evaluation of melanocyte ontogeny, human embryonic and fetal skin samples (n = 28) at 6-24 weeks gestation were studied immunohistochemically for expression of MITF and Mart-1. Adjacent step sections were evaluated to correlate staining patterns with cell localization in the intraepidermal, intrafollicular and intradermal compartments.
Results
At 6-8 weeks, MITF and Mart-1-positive cells were primarily intradermal with only rare positive cells in the epidermis. By 12-13 weeks, most of these cells had migrated into the epidermis, predominantly the suprabasal layers. Between 15-17 weeks, these cells localized to the basal layer and colonized developing hair follicles. Rare intradermal MITF and Mart-1 positive cells were found as late as week 20. At 18-24 weeks, MITF and Mart-1 positive cells were identified in the outer root sheath, bulge, and follicular bulge epithelium, in addition to the epidermis. Unexpectedly, weak but diffuse nuclear MITF expression was also present in the keratinocytes of the bulge area.
Conclusions
The in situ migratory fate of MITF/Mart-1-expressing cells in fetal skin involves a well-defined progression from intradermal to intraepidermal to intrafollicular localization. Occasional intradermal melanocytes may persist after the intraepithelial stages are completed, a finding of potential significance to melanocytic proliferations that may arise de novo within the dermis. Because MITF may play a role in stem cell maintenance, the presence of MITF in bulge epithelial cells suggests that it may be a novel marker for follicular stem cells of both epithelial and melanocytic lineage.
doi:10.1111/j.1600-0560.2007.00881.x
PMCID: PMC2935278  PMID: 18312434
9.  Dlx3 is a crucial regulator of hair follicle differentiation and regeneration 
Development (Cambridge, England)  2008;135(18):3149-3159.
SUMMARY
Dlx homeobox transcription factors regulate epidermal, neural and osteogenic cellular differentiation. Here we demonstrate the central role of Dlx3 as a crucial transcriptional regulator of hair formation and regeneration. The selective ablation of Dlx3 in the epidermis results in complete alopecia due to failure of the hair shaft and inner root sheath to form, which is caused by the abnormal differentiation of the cortex. Significantly, we elucidate the regulatory cascade that positions Dlx3 downstream of Wnt signaling and as an upstream regulator of other transcription factors that regulate hf differentiation, such as Hoxc13 and Gata3. Co-localization of phospho-SMAD1/5/8 and Dlx3 is consistent with a regulatory role of BMP signaling of Dlx3 during hair morphogenesis. Importantly, mutant catagen follicles undergo delayed regression and display persistent proliferation. Moreover, ablation of Dlx3 expression in the telogen bulge stem cells is associated with a loss of BMP signaling, precluding re-initiation of the hf growth cycle. Taken together with hf abnormalities in humans with Tricho-Dento-Osseous (TDO) syndrome, an autosomal dominant ectodermal dysplasia linked to mutations in the DLX3 gene, our results establish that Dlx3 is essential for hair morphogenesis, differentiation and cycling programs.
doi:10.1242/dev.022202
PMCID: PMC2707782  PMID: 18684741
10.  Association of Azospirillum with Grass Roots † 
The association between grass roots and Azospirillum brasilense Sp 7 was investigated by the Fahraeus slide technique, using nitrogen-free medium. Young inoculated roots of pearl millet and guinea grass produced more mucilaginous sheath (mucigel), root hairs, and lateral roots than did uninoculated sterile controls. The bacteria were found within the mucigel that accumulated on the root cap and along the root axes. Adherent bacteria were associated with granular material on root hairs and fibrillar material on undifferentiated epidermal cells. Significantly fewer numbers of azospirilla attached to millet root hairs when the roots were grown in culture medium supplemented with 5 mM potassium nitrate. Under these growth conditions, bacterial attachment to undifferentiated epidermal cells was unaffected. Aseptically collected root exudate from pearl millet contained substances which bound to azospirilla and promoted their adsorption to the root hairs. This activity was associated with nondialyzable and proteasesensitive substances in root exudate. Millet root hairs adsorbed azospirilla in significantly higher numbers than cells of Rhizobium, Pseudomonas, Azotobacter, Klebsiella, or Escherichia. Pectolytic activities, including pectin transeliminase and endopolygalacturonase, were detected in pure cultures of A. brasilense when this species was grown in a medium containing pectin. These studies describe colonization of grass root surfaces by A. brasilense and provide a possible explanation for the limited colonization of intercellular spaces of the outer root cortex.
Images
PMCID: PMC291307  PMID: 16345490
11.  Cortical Aerenchyma Formation in Hypocotyl and Adventitious Roots of Luffa cylindrica Subjected to Soil Flooding 
Annals of Botany  2007;100(7):1431-1439.
Background and Aims
Aerenchyma formation is thought to be one of the important morphological adaptations to hypoxic stress. Although sponge gourd is an annual vegetable upland crop, in response to flooding the hypocotyl and newly formed adventitious roots create aerenchyma that is neither schizogenous nor lysigenous, but is produced by radial elongation of cortical cells. The aim of this study is to characterize the morphological changes in flooded tissues and the pattern of cortical aerenchyma formation, and to analyse the relative amount of aerenchyma formed.
Method
Plants were harvested at 16 d after the flooding treatment was initiated. The root system was observed, and sections of fresh materials (hypocotyl, tap root and adventitious root) were viewed with a light or fluorescence microscope. Distributions of porosity along adventitious roots were estimated by a pycnometer method.
Key Results
Under flooded conditions, a considerable part of the root system consisted of new adventitious roots which soon emerged and grew quickly over the soil surface. The outer cortical cells of these roots and those of the hypocotyl elongated radially and contributed to the development of large intercellular spaces. The elongated cortical cells of adventitious roots were clearly T-shaped, and occurred regularly in mesh-like lacunate structures. In these positions, slits were formed in the epidermis. In the roots, the enlargement of the gas space system began close to the apex in the cortical cell layers immediately beneath the epidermis. The porosity along these roots was 11–45 %. In non-flooded plants, adventitious roots were not formed and no aerenchyma developed in the hypocotyl or tap root.
Conclusions
Sponge gourd aerenchyma is produced by the unique radial elongation of cells that make the expansigeny. These morphological changes seem to enhance flooding tolerance by promoting tissue gas exchange, and sponge gourd might thereby adapt to flooding stress.
doi:10.1093/aob/mcm239
PMCID: PMC2759224  PMID: 17921518
Aerenchyma; Luffa cylindrica; primary cortex; flooding; oxygen; adventitious root; hypocotyl; porosity
12.  Integrin-linked kinase is required for epidermal and hair follicle morphogenesis 
The Journal of Cell Biology  2007;177(3):501-513.
Integrin-linked kinase (ILK) links integrins to the actin cytoskeleton and is believed to phosphorylate several target proteins. We report that a keratinocyte-restricted deletion of the ILK gene leads to epidermal defects and hair loss. ILK-deficient epidermal keratinocytes exhibited a pronounced integrin-mediated adhesion defect leading to epidermal detachment and blister formation, disruption of the epidermal–dermal basement membrane, and the translocation of proliferating, integrin-expressing keratinocytes to suprabasal epidermal cell layers.
The mutant hair follicles were capable of producing hair shaft and inner root sheath cells and contained stem cells and generated proliferating progenitor cells, which were impaired in their downward migration and hence accumulated in the outer root sheath and failed to replenish the hair matrix. In vitro studies with primary ILK-deficient keratinocytes attributed the migration defect to a reduced migration velocity and an impaired stabilization of the leading-edge lamellipodia, which compromised directional and persistent migration. We conclude that ILK plays important roles for epidermis and hair follicle morphogenesis by modulating integrin-mediated adhesion, actin reorganization, and plasma membrane dynamics in keratinocytes.
doi:10.1083/jcb.200608125
PMCID: PMC2064816  PMID: 17485490
13.  Brassinosteroids control root epidermal cell fate via direct regulation of a MYB-bHLH-WD40 complex by GSK3-like kinases 
eLife  2014;3:e02525.
In Arabidopsis, root hair and non-hair cell fates are determined by a MYB-bHLH-WD40 transcriptional complex and are regulated by many internal and environmental cues. Brassinosteroids play important roles in regulating root hair specification by unknown mechanisms. Here, we systematically examined root hair phenotypes in brassinosteroid-related mutants, and found that brassinosteroid signaling inhibits root hair formation through GSK3-like kinases or upstream components. We found that with enhanced brassinosteroid signaling, GL2, a cell fate marker for non-hair cells, is ectopically expressed in hair cells, while its expression in non-hair cells is suppressed when brassinosteroid signaling is reduced. Genetic analysis demonstrated that brassinosteroid-regulated root epidermal cell patterning is dependent on the WER-GL3/EGL3-TTG1 transcriptional complex. One of the GSK3-like kinases, BIN2, interacted with and phosphorylated EGL3, and EGL3s mutated at phosphorylation sites were retained in hair cell nuclei. BIN2 phosphorylated TTG1 to inhibit the activity of the WER-GL3/EGL3-TTG1 complex. Thus, our study provides insights into the mechanism of brassinosteroid regulation of root hair patterning.
DOI: http://dx.doi.org/10.7554/eLife.02525.001
eLife digest
Roots anchor a plant into the ground, and allow the plant to absorb water and mineral nutrients from the soil. As roots grow and branch, they increase the surface area of root exposed to the soil—and many plant cells in the root's outer layer have a hair-like projection to further increase this surface area. Thus, root hairs are where most water and mineral nutrients are absorbed. Many factors affect whether, or not, a plant cell will develop into a root hair. These factors include both external cues (such as the mineral content of the soil) and signals from the plant itself (such as hormones).
Brassinosteroids are plant hormones that regulate the development of shoots and roots, as well as the timing of when flowers begin to develop. These hormones are detected on the outside of plant cells, and activate a signaling pathway within the cell that causes changes in gene expression. Brassinosteroids also control if a root cell will become a hair cell or not, although the mechanism behind this activity is unclear.
Here, Cheng et al. have looked at the root hairs of mutant Arabidopsis thaliana plants that have had individual genes involved in brassinosteroid signaling knocked-out. Plant biologists commonly study this plant species because it is small and grows quickly—and Arabidopsis has regular stripes of root hair cells and ‘non-hair cells’ in the outer layer of its roots. Cheng et al. reveal that brassinosteroids prevent the formation of root hairs via signaling pathways that involve proteins called GSK3-like kinases. These hormones ‘switch off’ these kinases’ activity, so knocking-out the genes that code for these kinases has the same effect as adding extra brassinosteroids to the plant roots: fewer root hair cells.
Cheng et al. show that one of the GSK3-like kinases binds and adds phosphate groups to protein complexes that control gene expression—and this causes these protein complexes to be less active. When GSK3-like kinase activity is switched off by brassinosteroids, these complexes instead become more active and trigger the expression of genes that direct a plant cell to become a non-hair cell.
The findings of Cheng et al. reveal the pathways that allow brassinosteroids to stop plant cells in roots from becoming hair cells, and that instead encourage these cells to become non-hair cells. However, further work is needed to uncover how the striped pattern of hair cells and non-hair cells on Arabidopsis roots is established, and how brassinosteroids work with other plant hormones to control this pattern.
DOI: http://dx.doi.org/10.7554/eLife.02525.002
doi:10.7554/eLife.02525
PMCID: PMC4005458  PMID: 24771765
brassinosteroids; GSK3-like kinases; root epidermal cell fate; EGL3; phosphorylation; TTG1; Arabidopsis
14.  A conceptual model of root hair ideotypes for future agricultural environments: what combination of traits should be targeted to cope with limited P availability? 
Annals of Botany  2012;112(2):317-330.
Background
Phosphorus (P) often limits crop production and is frequently applied as fertilizer; however, supplies of quality rock phosphate for fertilizer production are diminishing. Plants have evolved many mechanisms to increase their P acquisition, and an understanding of these traits could result in improved long-term sustainability of agriculture. This Viewpoint focuses on the potential benefits of root hairs to sustainable production.
Scope
First the various root-related traits that could be deployed to improve agricultural sustainability are catalogued, and their potential costs and benefits to the plant are discussed. A novel mathematical model describing the effects of length, density and longevity of root hairs on P acquisition is developed, and the relative benefits of these three root-hair traits to plant P nutrition are calculated. Insights from this model are combined with experimental data to assess the relative benefits of a range of root hair ideotypes for sustainability of agriculture.
Conclusions
A cost–benefit analysis of root traits suggests that root hairs have the greatest potential for P acquisition relative to their cost of production. The novel modelling of root hair development indicates that the greatest gains in P-uptake efficiency are likely to be made through increased length and longevity of root hairs rather than by increasing their density. Synthesizing this information with that from published experiments we formulate six potential ideotypes to improve crop P acquisition. These combine appropriate root hair phenotypes with architectural, anatomical and biochemical traits, such that more root-hair zones are produced in surface soils, where P resources are found, on roots which are metabolically cheap to construct and maintain, and that release more P-mobilizing exudates. These ideotypes could be used to inform breeding programmes to enhance agricultural sustainability.
doi:10.1093/aob/mcs231
PMCID: PMC3698376  PMID: 23172412
Arabidopsis; barley; Hordeum vulgare; cost/benefit; modelling; phosphorus; root architecture; root anatomy; root function; root hairs
15.  Generation of folliculogenic human epithelial stem cells from induced pluripotent stem cells 
Nature communications  2014;5:3071.
Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling. The isolation and propagation of human EpSCs for tissue engineering purposes remains a challenge. Here we develop a strategy to differentiate human iPSCs (hiPSCs) into CD200+/ITGA6+ EpSCs that can reconstitute the epithelial components of the hair follicle and interfollicular epidermis. The hiPSC-derived CD200+/ITGA6+ cells show a similar gene expression signature as EpSCs directly isolated from human hair follicles. Human iPSC-derived CD200+/ITGA6+ cells are capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths in skin reconstitution assays. The regenerated hair follicles possess a KRT15+ stem cell population and produce hair shafts expressing hair specific keratins. These results suggest an approach for generating large numbers of human EpSCs for tissue engineering and new treatments for hair loss, wound healing and other degenerative skin disorders.
doi:10.1038/ncomms4071
PMCID: PMC4049184  PMID: 24468981
16.  Computational identification of root hair-specific genes in Arabidopsis 
Plant Signaling & Behavior  2010;5(11):1407-1418.
Activated cortical domains (AC Ds) are regions of the plant cell cortex performing localized membrane turnover, delimited by concerted action of the cortical cytoskeleton and endomembrane compartments. Arabidopsis thaliana rhizodermis consists of two cell types differing by a single AC D (trichoblasts, carrying tip-growing root hairs, and hairless atrichoblasts), providing a model for the study of AC D determination. We compiled a set of genes specifically upregulated in root hairs from published transcriptome data and compared it with a “virtual Arabidopsis root hair proteome,” i.e., a list of computationally identified homologs of proteins from the published soybean root hair proteome. Both data sets were enriched in genes and proteins associated with root hairs in functional studies, but there was little overlap between the transcriptome and the proteome: the former captured gene products specific to root hairs, while the latter selected those abundant in root hairs but not necessarily specific to them. Decisive steps in AC D specification may be performed by signaling proteins of high expression specifity and low abundance. Nevertheless, 73 genes specifically transcribed in Arabidopsis trichoblasts or root hairs encode homologs of abundant root hair proteins from soybean. Most of them encode “housekeeping” proteins required for rapid tip growth. However, among the “candidates” is also a generative actin isoform, ACT11. Preliminary characterization of an act11 mutant allele indeed suggests a hitherto unexpected role for this gene in root and root hair development.
doi:10.4161/psb.5.11.13358
PMCID: PMC3115242  PMID: 21051945
activated cortical domain; transcriptome; proteome; tip growth; data mining; actin; root hair
17.  The organization of roots of dicotyledonous plants and the positions of control points 
Annals of Botany  2010;107(7):1213-1222.
Background
The structure of roots has been studied for many years, but despite their importance to the growth and well-being of plants, most researchers tend to ignore them. This is unfortunate, because their simple body plan makes it possible to study complex developmental pathways without the complications sometimes found in the shoot. In this illustrated essay, my objective is to describe the body plan of the root and the root apical meristem (RAM) and point out the control points where differentiation and cell cycle decisions are made. Hopefully this outline will assist plant biologists in identifying the structural context for their observations.
Scope and Conclusions
This short paper outlines the types of RAM, i.e. basic-open, intermediate-open and closed, shows how they are similar and different, and makes the point that the structure and shape of the RAM are not static, but changes in shape, size and organization occur depending on root growth rate and development stage. RAMs with a closed organization lose their outer root cap layers in sheets of dead cells, while those with an open organization release living border cells from the outer surfaces of the root cap. This observation suggests a possible difference in the mechanisms whereby roots with different RAM types communicate with soil-borne micro-organisms. The root body is organized in cylinders, sectors (xylem and phloem in the vascular cylinder), cell files, packets and modules, and individual cells. The differentiation in these root development units is regulated at control points where genetic regulation is needed, and the location of these tissue-specific control points can be modulated as a function of root growth rate. In Arabidopsis thaliana the epidermis and peripheral root cap develop through a highly regulated series of steps starting with a periclinal division of an initial cell, the root cap/protoderm (RCP) initial. The derivative cells from the RCP initial divide into two cells, the inner cell divides again to renew the RCP and the other cell divides through four cycles to form 16 epidermal cells in a packet; the outer cell divides through four cycles to form the 16 cells making up the peripheral root cap packet. Together, the epidermal packet and the peripheral root cap packet make up a module of cells which are clonally related.
doi:10.1093/aob/mcq229
PMCID: PMC3091796  PMID: 21118839
Root apical meristem; RAM; cell cycle; differentiation; peripheral root cap; closed RAM organization; open RAM organization; epidermis; module; determination; levels of organization; plasmodesmata; T-division; root cap/protoderm initial; columella initial
18.  Inhibition of BMP signaling in P-Cadherin positive hair progenitor cells leads to trichofolliculoma-like hair follicle neoplasias 
Background
Skin stem cells contribute to all three major lineages of epidermal appendages, i.e., the epidermis, the hair follicle, and the sebaceous gland. In hair follicles, highly proliferative committed progenitor cells, called matrix cells, are located at the base of the follicle in the hair bulb. The differentiation of these early progenitor cells leads to specification of a central hair shaft surrounded by an inner root sheath (IRS) and a companion layer. Multiple signaling molecules, including bone morphogenetic proteins (BMPs), have been implicated in this process.
Methods
To further probe the contribution of BMP signaling to hair follicle development and maintenance we employed a transgenic mouse that expresses the BMP inhibitor, Noggin, to disrupt BMP signaling specifically in subset of hair follicle progenitors under the control of neuron specific enolase (Nse) promoter. We then studied the skin tumor phenotypes of the transgenic mice through histology, immunohistochemistry and Western Blotting to delineate the underlying mechanisms. Double transgenic mice expressing BMP as well as noggin under control of the Nse promoter were used to rescue the skin tumor phenotypes.
Results
We found that the transgene is expressed specifically in a subpopulation of P-cadherin positive progenitor cells in Nse-Noggin mice. Blocking BMP signaling in this cell population led to benign hair follicle-derived neoplasias resembling human trichofolliculomas, associated with down-regulation of E-cadherin expression and dynamic regulation of CD44.
Conclusions
These observations further define a critical role for BMP signaling in maintaining the homeostasis of hair follicles, and suggest that dysregulation of BMP signaling in hair follicle progenitors may contribute to human trichofolliculoma.
doi:10.1186/1423-0127-18-92
PMCID: PMC3262035  PMID: 22168923
Transgenic Mice; Nse-Noggin; bone morphogenetic protein (BMP); trichofolliculoma
19.  PHIV-RootCell: a supervised image analysis tool for rice root anatomical parameter quantification 
We developed the PHIV-RootCell software to quantify anatomical traits of rice roots transverse section images. Combined with an efficient root sample processing method for image acquisition, this program permits supervised measurements of areas (those of whole root section, stele, cortex, and central metaxylem vessels), number of cell layers and number of cells per cell layer. The PHIV-RootCell toolset runs under ImageJ, an independent operating system that has a license-free status. To demonstrate the usefulness of PHIV-RootCell, we conducted a genetic diversity study and an analysis of salt stress responses of root anatomical parameters in rice (Oryza sativa L.). Using 16 cultivars, we showed that we could discriminate between some of the varieties even at the 6 day-olds stage, and that tropical japonica varieties had larger root sections due to an increase in cell number. We observed, as described previously, that root sections become enlarged under salt stress. However, our results show an increase in cell number in ground tissues (endodermis and cortex) but a decrease in external (peripheral) tissues (sclerenchyma, exodermis, and epidermis). Thus, the PHIV-RootCell program is a user-friendly tool that will be helpful for future genetic and physiological studies that investigate root anatomical trait variations.
doi:10.3389/fpls.2014.00790
PMCID: PMC4298167  PMID: 25646121
cell number; image analysis software; rice; root; tissue area; transverse histological section; histological phenotype scoring
20.  HISTOLOGY AND CYTOCHEMISTRY OF HUMAN SKIN  
1. Various amounts of β-glucuronidase activity may be found in all of the cutaneous appendages. 2. In the epidermis, the basal layer and the Malpighian layer contain a moderate amount of it, but a band of cells, including the stratum granulosum and the cells immediately above it, is rich in β-glucuronidase. 3. The cells of the duct of eccrine sweat glands have moderately strong enzyme activity, but those in the secretory coil are strongly reactive; small and large reactive granules are crowded in the reactive cytoplasm. 4. The cells of the secretory coil of the apocrine glands contain more β-glucuronidase than any other cutaneous appendage. 5. In the sebaceous glands, a very strong concentration of enzyme activity is found in the undifferentiated peripheral cells, a smaller amount of it is found in the differentiating cells. 6. In active hair follicles, the largest amount of β-glucuronidase is found in the outer root sheath and in the bulb. In the outer sheath, the strongest concentration is found around the level of the keratogenous zone of the cortex. The dermal papilla is strongly reactive. In quiescent hair follicles, the outer root sheath has a moderate amount of enzyme concentration, but the dermal papilla is unreactive. 7. In the dermis, the fibroblasts in the papillary layer, the smooth muscle cells of the arrectores pilorum and the tunica media of arteries, and the fat cells all exhibit enzyme activity. Mast cells show a great concentration of β-glucuronidase.
PMCID: PMC2224043  PMID: 13438919
21.  ILK modulates epithelial polarity and matrix formation in hair follicles 
Molecular Biology of the Cell  2014;25(5):620-632.
Integrin-linked kinase–deficient hair follicles fail to develop apical–basal polarity and show impaired specification of the hair matrix cell lineage. Exogenous laminin-511 restores matrix cell formation.
Hair follicle morphogenesis requires coordination of multiple signals and communication between its epithelial and mesenchymal constituents. Cell adhesion protein platforms, which include integrins and integrin-linked kinase (ILK), are critical for hair follicle formation. However, their precise contribution to this process is poorly understood. We show that in the absence of ILK, the hair follicle matrix lineage fails to develop, likely due to abnormalities in development of apical–basal cell polarity, as well as in laminin-511 and basement membrane assembly at the tip of the hair bud. These defects also result in impaired specification of hair matrix and absence of precortex and inner sheath root cell lineages. The molecular pathways affected in ILK-deficient follicles are similar to those in the absence of epidermal integrin β1 and include Wnt, but not sonic hedgehog, signaling. ILK-deficient hair buds also show abnormalities in the dermal papilla. Addition of exogenous laminin-511 restores morphological and molecular markers associated with hair matrix formation, indicating that ILK regulates hair bud cell polarity and functions upstream from laminin-511 assembly to regulate the developmental progression of hair follicles beyond the germ stage.
doi:10.1091/mbc.E13-08-0499
PMCID: PMC3937088  PMID: 24371086
22.  A STUDY OF THE ULTRASTRUCTURAL LOCALIZATION OF HAIR KERATIN SYNTHESIS UTILIZING ELECTRON MICROSCOPIC AUTORADIOGRAPHY IN A MAGNETIC FIELD 
The Journal of Cell Biology  1964;21(1):63-74.
The sites of the incorporation of labeled cystine into keratinizing structures were studied in electron microscopic autoradiographs. The tracer used was cystine labeled with S35 emitting long-range ionizing particles. During exposure for 1 to 2 months, according to our method of electron microscopic autoradiography, emulsion-coated specimens were exposed to a static magnetic field which appeared to result in a marked increase in the number of reacted silver grains. In young Swiss mice receiving intraperitoneal injections at 1, 3, and 6 hours before biopsy, conventional autoradiography demonstrated that S35-cystine was intensely localized in the keratogenous zone of anagen hair follicles, and that the radioactivity there increased in intensity progressively with time while the radioactivity in the hair bulb always remained very low. Our observations with electron microscopic autoradiography in a magnetic field appeared to indicate that at 3 and 6 hours after injection the S35-cystine was directly and specifically incorporated into tonofibrils in the hair cortex and into amorphous keratin granules of the hair cuticle layer, possibly without any particular concentration of this substance in the other cellular components. There seemed to be an appreciable concentration of cystine in tonofibrils of the cuticle of the inner root sheath. However, trichohyalin granules in the hair medulla and inner root sheath failed to show any evidence of cystine concentration. The improved sensitivity of the electron microscopic autoradiography with S35-cystine appeared to be partly due to the application of a static magnetic field. However, the reason for this could not be explained theoretically.
PMCID: PMC2106418  PMID: 14154496
23.  Anatomical aspects of angiosperm root evolution 
Annals of Botany  2013;112(2):223-238.
Background and Aims
Anatomy had been one of the foundations in our understanding of plant evolutionary trends and, although recent evo-devo concepts are mostly based on molecular genetics, classical structural information remains useful as ever. Of the various plant organs, the roots have been the least studied, primarily because of the difficulty in obtaining materials, particularly from large woody species. Therefore, this review aims to provide an overview of the information that has accumulated on the anatomy of angiosperm roots and to present possible evolutionary trends between representatives of the major angiosperm clades.
Scope
This review covers an overview of the various aspects of the evolutionary origin of the root. The results and discussion focus on angiosperm root anatomy and evolution covering representatives from basal angiosperms, magnoliids, monocots and eudicots. We use information from the literature as well as new data from our own research.
Key Findings
The organization of the root apical meristem (RAM) of Nymphaeales allows for the ground meristem and protoderm to be derived from the same group of initials, similar to those of the monocots, whereas in Amborellales, magnoliids and eudicots, it is their protoderm and lateral rootcap which are derived from the same group of initials. Most members of Nymphaeales are similar to monocots in having ephemeral primary roots and so adventitious roots predominate, whereas Amborellales, Austrobaileyales, magnoliids and eudicots are generally characterized by having primary roots that give rise to a taproot system. Nymphaeales and monocots often have polyarch (heptarch or more) steles, whereas the rest of the basal angiosperms, magnoliids and eudicots usually have diarch to hexarch steles.
Conclusions
Angiosperms exhibit highly varied structural patterns in RAM organization; cortex, epidermis and rootcap origins; and stele patterns. Generally, however, Amborellales, magnoliids and, possibly, Austrobaileyales are more similar to eudicots, and the Nymphaeales are strongly structurally associated with the monocots, especially the Acorales.
doi:10.1093/aob/mcs266
PMCID: PMC3698381  PMID: 23299993
Anatomy; angiosperms; cortex; epidermis; evolution; roots; vascular tissue
24.  Lateral root development in the maize (Zea mays) lateral rootless1 mutant 
Annals of Botany  2013;112(2):417-428.
Background and Aims
The maize lrt1 (lateral rootless1) mutant is impaired in its development of lateral roots during early post-embryonic development. The aim of this study was to characterize, in detail, the influences that the mutation exerts on lateral root initiation and the subsequent developments, as well as to describe the behaviour of the entire plant under variable environmental conditions.
Methods
Mutant lrt1 plants were cultivated under different conditions of hydroponics, and in between sheets of moist paper. Cleared whole mounts and anatomical sections were used in combination with both selected staining procedures and histochemical tests to follow root development. Root surface permeability tests and the biochemical quantification of lignin were performed to complement the structural data.
Key Results
The data presented suggest a redefinition of lrt1 function in lateral roots as a promoter of later development; however, neither the complete absence of lateral roots nor the frequency of their initiation is linked to lrt1 function. The developmental effects of lrt1 are under strong environmental influences. Mutant primordia are affected in structure, growth and emergence; and the majority of primordia terminate their growth during this last step, or shortly thereafter. The lateral roots are impaired in the maintenance of the root apical meristem. The primary root shows disturbances in the organization of both epidermal and subepidermal layers. The lrt1-related cell-wall modifications include: lignification in peripheral layers, the deposition of polyphenolic substances and a higher activity of peroxidase.
Conclusions
The present study provides novel insights into the function of the lrt1 gene in root system development. The lrt1 gene participates in the spatial distribution of initiation, but not in its frequency. Later, the development of lateral roots is strongly affected. The effect of the lrt1 mutation is not as obvious in the primary root, with no influences observed on the root apical meristem structure and maintenance; however, development of the epidermis and cortex are impaired.
doi:10.1093/aob/mct043
PMCID: PMC3698386  PMID: 23456690
Zea mays; lrt1; lateral root; lateral root emergence; root apical meristem; lignin; peroxidase
25.  A Gene Regulatory Network for Root Epidermis Cell Differentiation in Arabidopsis 
PLoS Genetics  2012;8(1):e1002446.
The root epidermis of Arabidopsis provides an exceptional model for studying the molecular basis of cell fate and differentiation. To obtain a systems-level view of root epidermal cell differentiation, we used a genome-wide transcriptome approach to define and organize a large set of genes into a transcriptional regulatory network. Using cell fate mutants that produce only one of the two epidermal cell types, together with fluorescence-activated cell-sorting to preferentially analyze the root epidermis transcriptome, we identified 1,582 genes differentially expressed in the root-hair or non-hair cell types, including a set of 208 “core” root epidermal genes. The organization of the core genes into a network was accomplished by using 17 distinct root epidermis mutants and 2 hormone treatments to perturb the system and assess the effects on each gene's transcript accumulation. In addition, temporal gene expression information from a developmental time series dataset and predicted gene associations derived from a Bayesian modeling approach were used to aid the positioning of genes within the network. Further, a detailed functional analysis of likely bHLH regulatory genes within the network, including MYC1, bHLH54, bHLH66, and bHLH82, showed that three distinct subfamilies of bHLH proteins participate in root epidermis development in a stage-specific manner. The integration of genetic, genomic, and computational analyses provides a new view of the composition, architecture, and logic of the root epidermal transcriptional network, and it demonstrates the utility of a comprehensive systems approach for dissecting a complex regulatory network.
Author Summary
A current challenge in the field of developmental biology is to define the composition and organization of gene networks that direct the pattern and differentiation of cells, tissues, and organs. In this study, we address this problem using Arabidopsis root epidermis development, a relatively simple model for studies of cell pattern formation and differentiation in plants. We used a tissue-specific cell sorting approach to define more than 1,500 genes whose transcripts differentially accumulate in the developing root epidermis. A series of transcriptome analyses were performed with 17 root epidermal mutants and 2 plant hormone treatments to dissect the regulatory relationships between 208 core genes. In addition, gene expression information from a developmental time series dataset was used to organize genes temporally. The results provide insight into the composition, organization, and logic of a developmental gene regulatory network. Furthermore, this work demonstrates the utility of an integrated analysis in gene regulatory network construction using genetic, genomic, and computational approaches.
doi:10.1371/journal.pgen.1002446
PMCID: PMC3257299  PMID: 22253603

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