The dynamic process of cell fate specification is regulated by networks of regulatory genes. The architecture of the network defines the temporal order of specification events. To understand the dynamic control of the developmental process, the kinetics of mRNA and protein synthesis and the response of the cis-regulatory modules to transcription factor concentration must be considered. Here we review mathematical models for mRNA and protein synthesis kinetics which are based on experimental measurements of the rates of the relevant processes. The model comprises the response functions of cis-regulatory modules to their transcription factor inputs, by incorporating binding site occupancy and its dependence on biologically measurable quantities. We use this model to simulate gene expression, to distinguish between cis-regulatory execution of “AND” and “OR” logic functions, rationalize the oscillatory behavior of certain transcriptional auto-repressors and to show how linked subcircuits can be dealt with. Model simulations display the effects of mutation of binding sites, or perturbation of upstream gene expression. The model is a generally useful tool for understanding gene regulation and the dynamics of cell fate specification.
Mathematical modeling; Gene regulation in development; Dynamics; Logic functions
Myf5 is a member of the muscle-specific determination genes and plays a critical role in skeletal muscle development. Whereas the expression of Myf5 during embryonic and fetal myogenesis has been extensively studied, its expression in progenitors that will ultimately give rise to adult satellite cells, the stem cells responsible for muscle repair, is still largely unexplored. To investigate this aspect, we have generated a mouse strain carrying a CreER coding sequence in the Myf5 locus. In this strain, Tamoxifen-inducible Cre activity parallels endogenous Myf5 expression. Combining Myf5CreER and Cre reporter alleles, we were able to evaluate the contribution of cells expressing Myf5 at distinct developmental stages to the pool of satellite cells in adult hindlimb muscles. Although it was possible to trace back the origin of some rare satellite cells to a subpopulation of Myf5+ve progenitors in the limb buds at the late embryonic stage (~E12), a significant number of satellite cells arise from cells which expressed Myf5 for the first time at the fetal stage (~E15). These studies provide direct evidence that adult satellite cells derive from progenitors that first express the myogenic determination gene Myf5 during fetal stages of myogenesis.
Myf5; satellite cells; fetal myogenesis; skeletal muscle
Somatic gonadal niche cells control the survival, differentiation, and proliferation of germline stem cells. The establishment of this niche-stem cell relationship is critical, and yet the precursors to these two cell types are often born at a distance from one another. The simple C. elegans gonadal primordium, which contains two somatic gonad precursors (SGPs) and two primordial germ cells (PGCs), provides an accessible model for determining how stem cell and niche cell precursors first assemble during development. To visualize the morphogenetic events that lead to formation of the gonadal primordium, we generated transgenic strains to label the cell membranes of the SGPs and PGCs and captured time-lapse movies as the gonadal primordium formed. We identify three distinct phases of SGP behavior: posterior migration along the endoderm towards the PGCs, extension of a single long projection around the adjacent PGC, and a dramatic wrapping over the PGC surfaces. We show that the endoderm and PGCs are dispensable for SGP posterior migration and initiation of projections. However, both tissues are required for the final positioning of the SGPs and the morphology of their projections, and PGCs are absolutely required for SGP wrapping behaviors. Finally, we demonstrate that the basement membrane component laminin, which localizes adjacent to the developing gonadal primordium, is required to prevent the SGPs from over-extending past the PGCs. Our findings provide a foundation for understanding the cellular and molecular regulation of the establishment of a niche-stem cell relationship.
somatic gonad precursor; primordial germ cell; niche; gonad; laminin; cell migration
Anterioposterior vertebrate limb patterning is controlled by opposing action between Sonic Hedgehog (Shh) and the Gli3 transcriptional repressor. Unexpectedly, Gli3Δ699 mutant mice, which are thought to express only a Gli3 repressor and not the full-length activator, exhibit limb phenotypes inconsistent with those of Shh mutant mice. Therefore, it remains debatable whether Shh patterns the anterioposterior limb primarily by inhibiting generation of the Gli3 repressor. However, one caveat is that Gli3Δ699 may not be as potent as the natural form of Gli3 repressor because of the nature of the mutant allele. In the present study, we created a conditional Gli3 mutant allele that exclusively expresses Gli3 repressor in the presence of Cre recombinase. Using this mutant, we show that the phenotypes of mouse limbs expressing only the Gli3 repressor exhibit no or single digit, resembling those of Shh mutant limbs. Consistent with the limb phenotypes, the expression of genes dependent on Shh signaling is also inhibited in both mutants. This inhibition by the Gli3 repressor is independent of Shh. Thus, our study clarifies the current controversy and provides important genetic evidence to support the hypothesis that Shh patterns the anterioposterior limb primarily through the inhibition of Gli3 repressor formation.
Hedgehog; Gli3; limb patterning
Sensory and endoneurocrine tissues as diverse as the lens, the olfactory epithelium, the inner ear, the cranial sensory ganglia, and the anterior pituitary arise from a common pool of progenitors in the preplacodal ectoderm (PPE). Around late gastrulation, the PPE forms at the border surrounding the anterior neural plate, and expresses a unique set of evolutionarily conserved transcription regulators including Six1, Eya 1 and Eya2. Here, we describe the first report to generate and characterize the SIX1+ PPE cells from human ES cells by adherent differentiation. Before forming PPE cells, differentiating cultures first expressed the non-neural ectoderm specific transcriptional factors TFAP2A, GATA2, GATA3, DLX3, and DLX5, which are crucial in establishing the PPE competence. We demonstrated that bone morphogenetic protein (BMP) activity plays a transient but essential role in inducing expression of these PPE competence factors and eventually the PPE cells. Interestingly, we found that attenuating BMP signaling after establishing the competence state induces anterior placode precursors. By manipulating BMP and hedgehog signaling pathways, we further differentiate these precursors into restricted lineages including the lens placode and the oral ectoderm (pituitary precursor) cells. Finally, we also show that sensory neurons can be generated from human PPE cells, demonstrating the multipotency of the human ES-derived PPE cells.
differentiation; stem cells; preplacodal ectoderm; cranial placodes; multipotency; lens; adherent cultures
The tree-like architecture of the mammary gland is generated by branching morphogenesis, which is regulated by many signals from the microenvironment. Here we examined how signaling downstream of phosphoinositide 3-kinase (PI3K) regulates different steps of mammary branching using three-dimensional culture models of the mammary epithelial duct. We found that PI3K was required for both branch initiation and elongation. Activated Akt was enhanced at branch initiation sites where its negative regulator, PTEN, was blocked by signaling via Sprouty2 (SPRY2); inhibiting Akt prevented branch initiation. The pattern of SPRY2 expression, and thus of Akt activation and branch initiation, was controlled by mechanical signaling from endogenous cytoskeletal contractility. In contrast, activated GTP-bound Rac1 localized to the leading edge of nascent branches and was required for branch elongation. These data suggest that the PI3K network integrates mechanical and biochemical signaling to control branching morphogenesis of mammary epithelial cells.
Morphodynamics; Patterning; Mechanical stress
The Janus kinase/Signal transducers and activators of transcription (JAK/STAT) pathway determines cell fates by regulating gene expression. One example is the specification of the motile cells called border cells during Drosophila oogenesis. It has been established that too much or too little STAT activity disrupts follicle cell identity and cell motility, which suggests the signaling must be precisely regulated. Here, we find that Suppressor of cytokine signaling at 36E (Socs36E) is a necessary negative regulator of JAK/STAT signaling during border cell specification. We find when STAT signaling is too low to induce migration in the presumptive border cell population, nearby follicle cells uncharacteristically become invasive to enable efficient migration of the cluster. We generated a genetic null allele that reveals Socs36E is required in the anterior follicle cells to limit invasive behavior to an optimal number of cells. We further show Socs36E genetically interacts with the required STAT feedback inhibitor apontic (apt) and APT’s downstream target, mir-279, and provide evidence that suggests APT directly regulates Socs36E transcriptionally. Our work shows Socs36E plays a critical role in a genetic circuit that establishes a boundary between the motile border cell cluster and its non-invasive epithelial neighbors through STAT attenuation.
Socs36E; Drosophila; Border cells; JAK/STAT; Apontic; Cell motility; Cell fate
The Wnt1-Cre transgenic mouse line is extensively used in the study of the development of the neural crest and its derivatives and the midbrain. The Wnt1 gene has important developmental roles in formation of the midbrain–hindbrain boundary, regulation of midbrain size, and neurogenesis of ventral midbrain dopaminergic (mDA) neurons. Here, we report that Wnt1-Cre transgenic mice exhibit phenotypes in multiple aspects of midbrain development. Significant expansion of the midbrain and increased proliferation in the developing inferior colliculus is associated with ectopic expression of Wnt1. Marked elevation of Wnt1 expression in the ventral midbrain is correlated with disruption of the differentiation program of ventral mDA neurons. We find that these phenotypes can be attributed to ectopic expression of Wnt1 from the Wnt1-Cre transgene leading to the ectopic activation of canonical Wnt/β-catenin signaling. Since these caveats could complicate the utility of Wnt1-Cre in some developmental circumstances, we report a new Wnt1-Cre2 transgenic mouse line that can serve the same purposes as the original without the associated phenotypic complications. These studies reveal an important caveat to a widely-used reagent, provide an improved version of this reagent, and indicate that the original Wnt1-Cre transgenic mouse line may be useful as a gain of function model for interrogating Wnt signaling mechanisms in multiple aspects of midbrain development.
Neural crest; Wnt1-Cre; Midbrain; Wnt signaling; Dopaminergic neurons; Craniofacial
To determine whether initiation is rate-limiting in protein synthesis during the embryogenesis of sea urchins, polyribosome profiles of unfertilized eggs and cleavage, blastula and prism stage embryos were examined after incubation of the eggs and embryos in the presence and absence of low amounts of emetine, an inhibitor of polypeptide elongation. The ribosomes were radioactively labeled with [3H]uridine by injection of the adults during oogenesis so that we could monitor emetine-dependent shifts of monoribosomes to polyribosomes. Although initiation is not rate limiting in unfertilized eggs or 2- to 16-cell embryos of Strongylocentrotus purpuratus, it is rate limiting in blastula and prism embryos. We suggest that initiation becomes rate limiting to allow the selective translation of certain classes of mRNA during later development.
The retinoic acid receptors α, β and γ (RARα, RARβ and RARγ) are nuclear hormone receptors that regulate fundamental processes during embryogenesis, but their roles in skeletal development and growth remain unclear. To study skeletal-specific RAR function, we created conditional mouse mutants deficient in RAR expression in cartilage. We find that mice deficient in RARα and RARγ (or RARβ and RARγ) exhibit severe growth retardation obvious by about 3 weeks postnatally. Their growth plates are defective and, importantly, display a major drop in aggrecan expression and content. Mice deficient in RARα and RARβ, however, are virtually normal, suggesting that RARγ is essential. In good correlation, we find that RARγ is the most strongly expressed RAR in mouse growth plate and its expression characterizes the proliferative and pre-hypertrophic zones where aggrecan is strongly expressed also. By being avascular, those zones lack endogenous retinoids and thus RARγ is likely to exert ligand-less repressor function. Indeed, our data indicate that: aggrecan production is enhanced by RARγ over-expression in chondrocytes under retinoid-free culture conditions; production is further boosted by corepressor Zac1 or pharmacologic agents that enhance RAR repressor function; and RAR/Zac1 function on aggrecan expression may involve Sox proteins. In sum, our data reveal that RARs, and RARγ in particular, exert previously unappreciated roles in growth plate function and skeletal growth and regulate aggrecan expression and content. Since aggrecan is critical for growth plate function, its deficiency in RAR-mutant mice is likely to have contributed directly to their growth retardation.
Retinoic acid receptors; Skeletal growth; Aggrecan; Growth plate; Zac1; Transcriptional repressors
Craniofacial development requires an exquisitely timed and positioned cross-talk between the embryonic cephalic epithelia and mesenchyme. This cross-talk underlies the precise translation of patterning processes and information into distinct, appropriate skeletal morphologies. The molecular and cellular dialogue includes communication via secreted signaling molecules, including Fgf8, and effectors of their interpretation. Herein, we use genetic attenuation of Fgf8 in mice and perform gain-of-function mouse-chick chimeric experiments to demonstrate that significant character states of the frontonasal and optic skeletons are dependent on Fgf8. Notably, we show that the normal orientation and polarity of the nasal capsules and their developing primordia are dependent on Fgf8. We further demonstrate that Fgf8 is required for midfacial integration, and provide evidence for a role for Fgf8 in optic capsular development. Taken together, our data highlight Fgf8 signaling in craniofacial development as a plausible target for evolutionary selective pressures.
Fgf8; Nasal Capsule; Optic Capsule; Mouse; Ectoderm; Midface; Craniofacial; Trabecular Basal Plate; FEZ
During the evolution of the Diptera there is a dramatic modification of the embryonic ectoderm, whereby mosquitoes contain separate amnion and serosa lineages while higher flies such as D. melanogaster contain a single amnioserosa. Whole-genome transcriptome assays were performed with isolated serosa from A. gambiae embryos. These assays identified a large number of genes implicated in the production of the larval cuticle. In D. melanogaster, these genes are activated just once during embryogenesis, during late stages where they are used for the production of the larval cuticle. Evidence is presented that the serosal cells secrete a dedicated serosal cuticle, which protects A. gambiae embryos from desiccation. Detailed temporal microarray assays of mosquito gene expression profiles revealed that the cuticular genes display biphasic expression during A. gambiae embryogenesis, first in the serosa of early embryos and then again during late stages as seen in D. melanogaster. We discuss how evolutionary modifications in the well-defined dorsal-ventral patterning network led to the wholesale deployment of the cuticle biosynthesis pathway in early embryos of A. gambiae.
Glypicans are conserved cell surface heparan sulfate proteoglycans expressed in a spatiotemporally regulated manner in many developing tissues including the nervous system. Here, we show that Glypican-1 (GPC1) is expressed by trigeminal placode cells as they ingress and contribute to trigeminal sensory neurons in the chick embryo. Either expression of full-length or truncated GPC1 in vivo causes defects in trigeminal gangliogenesis in a manner that requires heparan sulfate side chains. This leads to either abnormal placodal differentiation or organization, respectively, with near complete loss of the ophthalmic (OpV) trigeminal ganglion in the most severe cases after over-expression of full-length GPC1. Interestingly, modulating GPC1 alters levels of endogenous Wnt signaling activity in the forming trigeminal ganglion, as indicated by Wnt-reporter expression. Accordingly, GPC1 over-expression phenocopies Wnt inhibition in causing loss of OpV placodal neurons. Furthermore, increased Wnt activity rescues the effects of GPC1 over-expression. Taken together, these results suggest that appropriate levels of GPC1 are essential for proper regulation of canonical Wnt signaling during differentiation and organization of trigeminal placodal cells into ganglia.
glypican; trigeminal ganglion; placode; Wnt
Vascular endothelial cells from 3- to 10-day-old chicken embryos were identified by the uptake of acetylated low density lipoprotein (Ac-LDL) and the presence of a von Willebrand-like factor. These were determined on cross sections of aortic arches as well as in cell cultures prepared from the arches. To visualize the uptake of Ac-LDL, the fluorescent probe l,r-dioctadecyl-l-3,3,3’,3’-tetramethyl-indo-carbocyanine perchlorate-Ac-LDL (DiI-Ac-LDL) was used. Following injection of the DiI-Ac-LDL probe into the embryonic heart, the endothelium of the aortic arches became specifically labeled. Also, following the administration of the probe to cell cultures, about 5–10% of the cells became DiI-positive. Indirect immunofluorescence with an antibody against von Willebrand (vW) factor also revealed specific staining of the endothelium of the aortic arches as well as of a subset of cells in cultures from aortic arches. These two histochemical markers were further used to identify the emergence of the endothelial cell lineage in the chicken blastodisc. Cultured cells from embryos incubated in ovo for 16 hr exhibited both uptake of DiI-Ac-LDL and expression of a vW-like factor. The proportion of these cells was about 30% of the total cultured cells and increased to over 50% in cultures of embryos incubated in ovo for 20 hr. However, cells positive for uptake of DiI-Ac-LDL and expression of vW-like factor were lacking in cultures of unincubated eggs or eggs incubated for 6–10 hr. We conclude that the very early endothelial cells in the chick blastodisc are already capable of expressing characteristic properties of vascular endothelium.
The cuticular hairs and sensory bristles that decorate the adult Drosophila epidermis and the denticles found on the embryo have been used in studies on planar cell polarity and as models for the cytoskeletal mediated morphogenesis of cellular extensions. ZP domain proteins have recently been found to be important for the morphogenesis of both denticles and bristles. Here we show that the ZP domain protein Dusky-Like is a key player in hair morphogenesis. As is the case in bristles, in hairs dyl mutants display a dramatic phenotype that is the consequence of a failure to maintain the integrity of the extension after outgrowth. Hairs lacking dyl function are split, thinned, multipled and often very short. dyl is required for normal chitin deposition in hairs, but chitin is not required for the normal accumulation of Dyl, hence dyl acts upstream of chitin. A lack of chitin however, does not mimic the dyl hair phenotype, thus Dyl must have other targets in hair morphogenesis. One of these appears to be the actin cytoskeleton. Interestingly, dyl mutants also display a unique planar cell polarity phenotype that is distinct from that seen with mutations in frizzled/starry night or dachsous/fat pathway genes. Rab11 was previously found to be essential for Dyl plasma membrane localization in bristles. Here we found that the expression of a dominant negative Rab11 can mimic the dyl hair morphology phenotype consistent with Rab11 also being required for Dyl function in hairs. We carried out a small directed screen to identify genes that might function with dyl and identified Chitinase 6 (Cht6) as a strong candidate, as knocking down Cht6 function led to weak versions of all of the dyl hair phenotypes.
dyl; Drosophila; wing hair; chitin; planar polarity
Understanding how and when the left-right (LR) axis is first established is a fundamental question in developmental biology. A popular model is that the LR axis is established relatively late in embryogenesis, due to the movement of motile cilia and the resultant directed fluid flow during late gastrulation/early neurulation. Yet, a large body of evidence suggests that biophysical, molecular, and bioelectrical asymmetries exist much earlier in development, some as early as the first cell cleavage after fertilization. Alternative models of LR asymmetry have been proposed that accommodate these data, postulating that asymmetry is established due to a chiral cytoskeleton and/or the asymmetric segregation of chromatids. There are some similarities, and many differences, in how these various models postulate the origin and timing of symmetry breaking and amplification, and these events’ linkage to the well-conserved subsequent asymmetric transcriptional cascades. This review examines experimental data that lend strong support to an early origin of LR asymmetry, yet are also consistent with later roles for cilia in the amplification of LR pathways. In this way, we propose that the various models of asymmetry can be unified: early events are needed to initiate LR asymmetry, and later events could be utilized by some species to maintain LR-biases. We also present an alternative hypothesis, which proposes that individual embryos stochastically choose one of several possible pathways with which to establish their LR axis. These two hypotheses are both tractable in appropriate model species; testing them to resolve open questions in the field of LR patterning will reveal interesting new biology of wide relevance to developmental, cell, and evolutionary biology.
asymmetry; left-right; laterality; chirality; cytoskeleton; cilia
Wntless (Wls), a gene highly conserved across the animal kingdom, encodes for a transmembrane protein that mediates Wnt ligand secretion. Wls is expressed in developing lung, wherein Wnt signaling is necessary for pulmonary morphogenesis. We hypothesize that Wls plays a critical role in modulating Wnt signaling during lung development and therefore affects processes critical for pulmonary morphogenesis. We generated conditional Wls mutant mice utilizing Shh-Cre and Dermo1-Cre mice to delete Wls in the embryonic respiratory epithelium and mesenchyme, respectively. Epithelial deletion of Wls disrupted lung branching morphogenesis, peripheral lung development and pulmonary endothelial differentiation. Epithelial Wls mutant mice died at birth due to respiratory failure caused by lung hypoplasia and pulmonary hemorrhage. In the lungs of these mice, VEGF and Tie2-angiopoietin signaling pathways, which mediate vascular development, were downregulated from early stages of development. In contrast, deletion of Wls in mesenchymal cells of the developing lung did not alter branching morphogenesis or early mesenchymal differentiation. In vitro assays support the concept that Wls acts in part via Wnt5a to regulate pulmonary vascular development. We conclude that epithelial Wls modulates Wnt ligand activities critical for pulmonary vascular differentiation and peripheral lung morphogenesis. These studies provide a new framework for understanding the molecular mechanisms underlying normal pulmonary vasculature formation and the dysmorphic pulmonary vasculature development associated with congenital lung disease.
Wntless; Wnt; lung development; endothelium; epithelium
Drosophila dMyc (dMyc) is known for its role in cell-autonomous regulation of growth. Here we address its role in the fat body (FB), a metabolic tissue that functions as a sensor of circulating nutrients to control the release of Drosophila Insulin-like peptides (Dilps) from the brain influencing growth and development. Our results show that expression of dMyc in the FB affects development and animal size. Expression of dMyc, but not of CycD/cdk4 or Rheb, in the FB diminishes the ability to retain Drosophila Insulin-like peptide-2 (DILP2) in the brain during starvation, suggesting that expression of dMyc mimics the signal that remotely controls the release of Dilps into the hemolymph. dMyc also affects glucose metabolism and increases the transcription of Glucose-transporter-1 mRNA, and of Hexokinase and Pyruvate-Kinase mRNAs, key regulators of glycolysis. These animals are able to counteract the increased levels of circulating trehalose induced by a high sugar diet leading to the conclusion that dMyc activity in the FB promotes glucose disposal. dMyc expression induces cell autonomous accumulation of triglycerides, which correlates with increased levels of Fatty Acid Synthase and Acetyl CoA Carboxylase mRNAs, enzymes responsible for lipid synthesis. We also found the expression of Stearoyl-CoA desaturase, Desat1 mRNA significantly higher in FB overexpressing dMyc. Desat1 is an enzyme that is necessary for monosaturation and production of fatty acids, and its reduction affects dMyc’s ability to induce fat storage and resistance to animal survival. In conclusion, here we present novel evidences for dMyc function in the Drosophila FB in controlling systemic growth. We discovered that dMyc expression triggers cell autonomous mechanisms that control glucose and lipid metabolism to favor the storage of nutrients (lipids and sugars). In addition, the regulation of Desat1 controls the synthesis of triglycerides in FB and this may affect the humoral signal that controls DILP2 release in the brain.
Myc; Drosophila; DILP2; Glycolysis; Trehalose; Fatty Acid Synthesis; Desat1
The MSP domain is a conserved immunoglobulin-like structure that is important for C. elegans reproduction and human motor neuron survival. C. elegans MSPs are the most abundant proteins in sperm, where they function as intracellular cytoskeletal proteins and secreted hormones. Secreted MSPs bind to multiple receptors on oocyte and ovarian sheath cell surfaces to induce oocyte maturation and sheath contraction. MSP binding stimulates oocyte MPK-1 ERK MAP Kinase (MAPK) phosphorylation, but the function and mechanism are not well understood. Here we show that the Shp class protein-tyrosine phosphatase PTP-2 acts in oocytes downstream of sheath/oocyte gap junctions to promote MSP-induced MPK-1 phosphorylation. PTP-2 functions in the oocyte cytoplasm, not at the cell surface to inhibit multiple RasGAPs, resulting in sustained Ras activation. We also provide evidence that MSP promotes production of reactive oxygen species (ROS), which act as second messengers to augment MPK-1 phosphorylation. The Cu/Zn superoxide dismutase SOD-1, an enzyme that catalyzes ROS breakdown in the cytoplasm, inhibits MPK-1 phosphorylation downstream of or in parallel to ptp-2. Our results support the model that MSP triggers PTP-2/Ras activation and ROS production to stimulate MPK-1 activity essential for oocyte maturation. We propose that secreted MSP domains and Cu/Zn superoxide dismutases function antagonistically to control ROS and MAPK signaling.
MSP; MAP Kinase; Oocyte Maturation; Shp; RasGAP; Ras; Fertilization; SOD1; Amyotrophic Lateral Sclerosis; VAPB; Reactive oxygen species
The emergence of avian satellite cells during development has been studied using markers that distinguish adult from fetal cells. Previous studies by us have shown that myogenic cultures from fetal (Embryonic Day 10) and adult (12–16 weeks) chicken pectoralis muscle (PM) each regulate expression of the embryonic isoform of fast myosin heavy chain (MHC) differently. In fetal cultures, embryonic MHC is coexpressed with a ventricular MHC in both myocytes (differentiated myoblasts) and myotubes. In contrast, myocytes and newly formed myotubes in adult cultures express ventricular but not embryonic MHC. In the current study, the appearance of myocytes and myotubes which express ventricular but not embryonic MHC was used to determine when adult myoblasts first emerge during avian development. By examining patterns of MHC expression in mass and clonal cultures prepared from embryonic and posthatch chicken skeletal muscle using double-label immunofluorescence with isoform-specific monoclonal antibodies, we show that a significant number of myocytes and myotubes which stain for ventricular but not embryonic MHC are first seen in cultures derived from PM during fetal development (Embryonic Day 18) and comprise the majority, if not all, of the myoblasts present at hatching and beyond. These results suggest that adult type myoblasts become dominant in late embryogenesis. We also show that satellite cell cultures derived from adult slow muscle give results similar to those of cultures derived from adult fast muscle. Cultures derived from Embryonic Day 10 hindlimb form myocytes and myotubes that coexpress ventricular and embryonic MHCs in a manner similar to cells of the Embryonic Day 10 PM. Thus, adult and fetal expression patterns of ventricular and embryonic MHCs are correlated with developmental age but not muscle fiber type.
Sperm motility is essential for achieving fertilization. In animals with external fertilization as amphibians, spermatozoa are stored in a quiescent state in the testis. Spermiation to hypotonic fertilization media triggers activation of sperm motility. Bufo arenarum sperm are immotile in artificial seminal plasma (ASP) but acquire in situ flagellar beating upon dilution. In addition to the effect of low osmolarity on sperm motility activation, we report that diffusible factors of the egg jelly coat (EW) regulate motility patterns, switching from in situ to progressive movement. The signal transduction pathway involved in amphibian sperm motility activation is mostly unknown. In the present study, we show a correlation between motility activation triggered by low osmotic pressure and activation of protein kinase A (PKA). Moreover, this is the first study to present strong evidences that point toward a role of a transmembrane adenyl-cyclase (tmAC) in the regulation of amphibian sperm motility through PKA activation.
Amphibia; sperm; motility activation; cAMP dependent kinase; adenylyl cyclase
Most studies to date indicate that the formation of testis cords is critical for proper Sertoli cell differentiation, inhibition of germ cell meiosis, and regulation of Leydig cell differentiation. However, the connections between these events are poorly understood. The objective of this study was to dissect the molecular and cellular relationships between these events in testis formation. We took advantage of the different effects of two hedgehog signaling inhibitors, cyclopamine and forskolin, on gonad explant cultures. Both hedgehog inhibitors phenocopied the disruptive effect of Dhh−/− on formation of testis cords without influencing Sertoli cell differentiation. However, they exhibited different effects on other cellular events during testis development. Treatment with cyclopamine did not affect inhibition of germ cell meiosis and mesonephric cell migration but caused defects in Leydig cell differentiation. In contrast, forskolin treatment induced germ cell meiosis, inhibited mesonephric cell migration, and had no effect on Leydig cell differentiation. By carefully contrasting the different effects of these two hedgehog inhibitors, we demonstrate that although formation of testis cords and development of other cell types normally take place in a tightly regulated sequence, each of these events can occur independent of the others.
Desert Hedgehog; Patched-1; Sertoli; Leydig; Germ cells; Meiosis; and PKA
It is the precise connectivity between skeletal muscles and their corresponding tendon cells to form a functional myotendinous junction (MTJ) that allows for the force generation required for muscle contraction and organismal movement. The Drosophila MTJ is comprised of secreted extracellular matrix (ECM) proteins deposited between integrin-mediated hemi-adherens junctions on the surface of muscle and tendon cells. In this paper, we have identified a novel, cytoplasmic role for the canonical nuclear import protein Moleskin (Msk) in Drosophila embryonic somatic muscle attachment. Msk protein is enriched at muscle attachment sites in late embryogenesis and msk mutant embryos exhibit a failure in muscle-tendon cell attachment. Although the muscle-tendon attachment sites are reduced in size, components of the integrin complexes and ECM proteins are properly localized in msk mutant embryos. However, msk mutants fail to localize phosphorylated Focal adhesion kinase (pFAK) to the sites of muscle-tendon cell junctions. In addition, the tendon cell specific proteins Stripe (Sr) and activated mitogen-activated protein kinase (MAPK) are reduced in msk mutant embryos. Our rescue experiments demonstrate that Msk is required in the muscle cell, but not in the tendon cells. Moreover, muscle attachment defects due to loss of Msk are rescued by an activated form of MAPK or the secreted Epidermal Growth Factor receptor (Egfr) ligand Vein. Taken together, these findings provide strong evidence that Msk signals non-autonomously through the Vein-Egfr signaling pathway for late tendon cell late differentiation and/or maintenance.
Drosophila; Muscle development; Moleskin; Myotendinous junction; MAPK
Tumor necrosis factor alpha receptor 3 interacting protein 1 (Traf3ip1), also known as MIPT3, was initially characterized through its interactions with tubulin, actin, TNFR-associated factor-3 (Traf3), IL-13R1, and DISC1. It functions as an inhibitor of IL-13-mediated phosphorylation of Stat6 and in sequestration of Traf3 and DISC1 to the cytoskeleton. Studies of the Traf3ip1 homologs in C. elegans (DYF-11), Zebrafish (elipsa), and Chlamydomonas (IFT54) revealed that the protein localizes to the cilium and is required for ciliogenesis. Similar localization data has now been reported for mammalian Traf3ip1. This raises the possibility that Traf3ip1 has an evolutionarily conserved role in mammalian ciliogenesis in addition to its previously indicated functions. To evaluate this possibility, a Traf3ip1 mutant mouse line was generated. Traf3ip1mutant cells are unable to form cilia. Homozygous Traf3ip1 mutant mice are not viable and have both neural developmental defects and polydactyly, phenotypes typical of mouse mutants with ciliary assembly defects. Furthermore, in Traf3ip1 mutants the hedgehog pathway is disrupted, as evidenced by abnormal dorsal-ventral neural tube patterning and diminished expression of a hedgehog reporter. Analysis of the canonical Wnt pathway indicates that it was largely unaffected; however, specific domains in the pharyngeal arches have elevated levels of reporter activity. Interestingly, Traf3ip1 mutant embryos and cells failed to show alterations in IL-13 signaling, one of the pathways associated with its initial discovery. Novel phenotypes observed in Traf3ip1 mutant cells include elevated cytosolic levels of acetylated microtubules and a marked increase in cell size in culture. The enlarged Traf3ip1 mutant cell size was associated with elevated basal mTor pathway activity. Taken together, these data demonstrate that Traf3ip1 function is highly conserved in ciliogenesis and is important for proper regulation of a number of essential developmental and cellular pathways. The Traf3ip1 mutant mouse and cell lines will provide valuable resources to assess cilia function in mammalian development and also serve as a tool to explore the potential connections between cilia and cytoskeletal dynamics, mTor regulation, and cell volume control.
primary cilia; IFT; Traf3ip1; MIPT3
The development of oligodendrocytes, the myelinating cells of the vertebrate CNS, is regulated by a cohort of growth factors and transcription factors. Less is known about the signaling pathways that integrate extracellular signals with intracellular transcriptional regulators to control oligodendrocyte development. Cyclin dependent kinase 5 (Cdk5) and its co-activators play critical roles in the regulation of neuronal differentiation, cortical lamination, neuronal cell migration and axon outgrowth. Here we demonstrate a previously unrecognized function of Cdk5 in regulating oligodendrocyte maturation and myelination. During late embryonic development Cdk5 null animals displayed a reduction in the number of MBP+ cells in the spinal cord, but no difference in the number of OPCs. To determine whether the reduction of oligodendrocytes reflected a cell-intrinsic loss of Cdk5, it was selectively deleted from Olig1+ oligodendrocyte lineage cells. In Olig1Cre/+; Cdk5fl/fl conditional mutants, reduced levels of expression of MBP and PLP mRNA were observed throughout the CNS and ultrastructural analyses demonstrated a significant reduction in the proportion of myelinated axons in the optic nerve and spinal cord. Pharmacological inhibition or RNAi knockdown of Cdk5 in vitro resulted in the reduction in oligodendrocyte maturation, but had no effect on OPC cell proliferation. Conversely, over-expression of Cdk5 promoted oligodendrocyte maturation and enhanced process outgrowth. Consistent with this data, Cdk5−/− oligodendrocytes developed significantly fewer primary processes and branches than control cells. Together, these findings suggest that Cdk5 function as a signaling integrator to regulate oligodendrocyte maturation and myelination.
conditional Cdk5 knockout; OPC; oligodendrocytes; differentiation; myelination