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1.  Incomplete Cre-mediated excision leads to phenotypic differences between Stra8-iCre; Mov10l1lox/lox and Stra8-iCre; Mov10l1lox/Δ mice 
Genesis (New York, N.Y. : 2000)  2013;51(7):481-490.
In the Cre-loxp system, expression level and activity of Cre recombinase in a Cre deletor line are critical because these determine not only the cell specificity of gene knockout (KO), but also the efficiency of Cre-mediated excision in a specific cell lineage. Although the spatiotemporal expression pattern of a Cre transgene is usually defined upon the generation of the mouse line, the Cre excision efficiency in a specific targeted cell lineage is rarely evaluated and often assumed to be 100%. Incomplete excision can lead to highly variable phenotypes due to mosaicism (i.e. co-existence of cells with the flox or the recombined flox allele) and this problem has long been overlooked. Here, we report that Stra8-iCre, a transgenic allele expressing codon-improved Cre recombinase (iCre) under the control of the male germ cell-specific Stra8 promoter, could efficiently delete one Mov10l1 flox allele in spermatogenic cells, whereas the excision was incomplete when two Mov10l1 flox alleles were present. The incomplete Cre-mediated excision led to a testicular phenotype that was much less severe than that in the true conditional KO (100% inactivation) mice. Our findings suggest that it is essential to determine the efficiency of Cre excision when Cre-loxp system is used for deleting genes in a specific cell lineage and the Cre; genelox / Δ genotype should be used to evaluate phenotypes instead of Cre; genelox/lox due to the fact that the latter usually bears incomplete deletion of the flox allele(s).
PMCID: PMC3918465  PMID: 23554062
conditional gene knockout; Cre; loxp; piRNA; testis; germ line; phenotype; mosaicism
2.  Etv2 rescues Flk1 mutant embryoid bodies 
Genesis (New York, N.Y. : 2000)  2013;51(7):471-480.
Independent mouse knockouts of Etv2 and Flk1 are embryonic lethal and lack hematopoietic and endothelial lineages. We previously reported that Flk1 activates Etv2 in the initiation of hematopoiesis and vasculogenesis. However, Flk1 and its ligand VEGF are expressed throughout development, from E7.0 to adulthood, whereas Etv2 is expressed only transiently during embryogenesis. These observations suggest a complex regulatory interaction between Flk1 and Etv2. To further examine the Flk1 and Etv2 regulatory interaction, we transduced Etv2 and Flk1 mutant ES cells with viral integrants that inducibly overexpress Flk1 or Etv2. We demonstrated that forced expression of Etv2 rescued the hematopoietic and endothelial potential of differentiating Flk1 and Etv2 mutant cells. We further discovered that forced expression of Flk1 can rescue that of the Flk1, but not Etv2 mutant cells. Therefore, we conclude that the requirement for Flk1 can be bypassed by expressing Etv2, supporting the notion that disruption of Etv2 expression is responsible for the early phenotypes of the Etv2 and Flk1 mutant embryos.
PMCID: PMC3987665  PMID: 23606617
vasculogenesis; hematopoiesis; development
3.  Colocalization of WT1 and Cell Proliferation Reveals Conserved Mechanisms in Temperature-Dependent Sex Determination 
Genesis (New York, N.Y. : 2000)  2003;35(4):193-201.
During vertebrate development the gonad has two possible fates, the testis or the ovary. The choice between these fates is made by a variety of sex-determining mechanisms, from the sex-determining gene on the Y chromosome (Sry) in mammals, to nongenetic temperature-dependent systems in many reptiles. Despite the differences in the mechanisms at the top of the sex-determining cascade, the resulting morphology and many genes involved in early testis and ovarian development are common to most vertebrates, leading to the hypothesis that the underlying processes of sex determination are conserved. In this study, we examined the early steps of gonad development in the red-eared slider turtle (Trachemys scripta), a species that uses the temperature of egg incubation to determine sex. A dramatic increase in cell proliferation was observed in the male gonad during the earliest stages of sex determination. Using the localization of Wilms’ Tumor suppressor 1 (WT1), we determined that this proliferation increase occurred in a population that contained pre-Sertoli cells. The proliferation of pre-Sertoli cells has been documented during sex determination in both mice and alligators, suggesting that proliferation of this cell type has an important role in vertebrate testis organogenesis and the determination of male fate.
PMCID: PMC4041374  PMID: 12717730
sex determination; gonad development; testis; Sertoli cell; turtle; WT1; cell proliferation; T. scripta
4.  Non-parallel recombination limits Cre-LoxP-based reporters as precise indicators of conditional genetic manipulation 
Genesis (New York, N.Y. : 2000)  2013;51(6):436-442.
Cre/LoxP-mediated recombination allows for conditional gene activation or inactivation. When combined with an independent lineage-tracing reporter allele, this technique traces the lineage of presumptive genetically modified Cre-expressing cells. Several studies have suggested that floxed alleles have differential sensitivities to Cre-mediated recombination, which raises concerns regarding utilization of common Cre-reporters to monitor recombination of other floxed loci of interest. Here, we directly investigate the recombination correlation, at cellular resolution, between several floxed alleles induced by Cre-expressing mouse lines. The recombination correlation between different reporter alleles varied greatly in otherwise genetically identical cell types. The chromosomal location of floxed alleles, distance between LoxP sites, sequences flanking the LoxP sites, and the level of Cre activity per cell all likely contribute to observed variations in recombination correlation. These findings directly demonstrate that, due to non-parallel recombination events, commonly available Cre reporter mice cannot be reliably utilized, in all cases, to trace cells that have DNA recombination in independent-target floxed alleles, and that careful validation of recombination correlations are required for proper interpretation of studies designed to trace the lineage of genetically modified populations, especially in mosaic situations.
PMCID: PMC3696028  PMID: 23441020
Mosaic analysis; lineage tracing; cell autonomous; Cre detection; non-parallel recombination
5.  Generation and characterization of KsprtTA and KsptTA transgenic mice 
Genesis (New York, N.Y. : 2000)  2013;51(6):430-435.
The advent of technologies that allow tissue specific expression or ablation of genes has contributed enormously to our knowledge of the mechanism regulating organ development and maintenance in mice. The tetracycline inducible system allows reversible regulation of gene products upon administration of Doxycycline. Here we describe the generation and activity of two transgenic lines expressing the cDNAs for the Tet responsive transcription factors rtTA and tTA (Tet-on and off) respectively under the control of an element that drives expression in the epithelium of the developing and adult kidney. Both lines show inducible and reversible activity in the embryonic and adult organ.
PMCID: PMC3696052  PMID: 23420736
Kidney development; kidney epithelium; kidney tubule; Tet-on; Tet-off
6.  Biallelic genome modification in F0 Xenopus tropicalis embryos using the CRISPR/Cas system 
Genesis (New York, N.Y. : 2000)  2013;51(12):827-834.
Gene inactivation is an important tool for correlation of phenotypic and genomic data, allowing researchers to infer normal gene function based on the phenotype when the gene function is impaired. New and better approaches are needed to overcome the shortfalls of existing methods for any significant acceleration of scientific progress. We have adapted the CRISPR/Cas system for use in Xenopus tropicalis and report on the efficient creation of mutations in the gene encoding the enzyme tyrosinase, which is responsible for oculocutaneous albinism. Biallelic mutation of this gene was detected in the F0 generation, suggesting targeting efficiencies similar to that of TALENs. We also find that off-target mutagenesis appears to be negligible and therefore CRISPR/Cas may be a useful system for creating genome modifications in this important model organism.
PMCID: PMC4039559  PMID: 24123579
TALENs; CRISPR/Cas; zinc finger nucleases; gene knockouts; gene targeting
7.  A Phox2b::FLPo transgenic mouse line suitable for intersectional genetics 
Genesis (New York, N.Y. : 2000)  2013;51(7):506-514.
Phox2b is a transcription factor expressed in the central and peripheral neurons that control cardiovascular, respiratory and digestive functions and essential for their development. Several populations known or suspected to regulate visceral functions express Phox2b in the developing hindbrain. Extensive cell migration and lack of suitable markers have greatly hampered studying their development. Reasoning that intersectional fate mapping may help to overcome these impediments, we have generated a BAC transgenic mouse line, P2b::FLPo, which expresses codon-optimized FLP recombinase in Phox2b expressing cells. By partnering the P2b::FLPo with the FLP-responsive RC::Fela allele, we show that FLP recombination switches on lineage tracers in the cells that express or have expressed Phox2b, permanently marking them for study across development. Taking advantage of the dualrecombinase feature of RC::Fela, we further show that the P2b::FLPo transgene can be partnered with Lbx1Cre as Cre driver to generate triple transgenics in which neurons having a history of both Phox2b and Lbx1 expression are specifically labelled. Hence, the P2b::FLPo line when partnered with a suitable Cre driver provides a tool for tracking and accessing genetically subsets of Phox2b-expressing neuronal populations, which has not been possible by Cremediated recombination alone.
PMCID: PMC4036463  PMID: 23592597
BAC transgenic mouse line; fate mapping; FLP recombinase; Phox2b; hindbrain
8.  Experimental approaches for gene regulatory network construction: the chick as a model system 
Genesis (New York, N.Y. : 2000)  2012;51(5):296-310.
Setting up the body plan during embryonic development requires the coordinated action of many signals and transcriptional regulators in a precise temporal sequence and spatial pattern. The last decades have seen an explosion of information describing the molecular control of many developmental processes. The next challenge is to integrate this information into logic ‘wiring diagrams’ that visualise gene actions and outputs, have predictive power and point to key control nodes. Here we provide an experimental workflow on how to construct gene regulatory networks using the chick as model system. Keywords: transcription factors, transcriptome analysis, conserved regulatory elements
PMCID: PMC3626748  PMID: 23174848
9.  Identification of adult mineralized tissue zebrafish mutants 
Genesis (New York, N.Y. : 2000)  2011;49(4):360-366.
Zebrafish craniofacial, skeletal, and tooth development closely resembles that of higher vertebrates. Our goal is to identify viable adult zebrafish mutants that can be used as models for human mineralized craniofacial, dental, and skeletal system disorders. We utilized a large-scale forward-genetic chemical N-ethyl-nitroso-urea (ENU) mutagenesis screen to identify 17 early lethal homozygous recessive mutants with defects in craniofacial cartilage elements, and 7 adult homozygous recessive mutants with mineralized tissue phenotypes including craniofacial shape defects, fused sutures, dysmorphic or missing skeletal elements, scoliosis, and neural arch defects. One mutant displayed both an early lethal homozygous phenotype and an adult heterozygous phenotype. These results extend the utility of the zebrafish model beyond the embryo, to study human bone and cartilage disorders.
PMCID: PMC3996835  PMID: 21225658
adult craniofacial; skeletal; tooth dysplasias
10.  Sox9-expressing Precursors Are the Cellular Origin of the Cruciate Ligament of the Knee Joint and the Limb Tendons 
Genesis (New York, N.Y. : 2000)  2010;48(11):635-644.
Sox9 expression defines cell progenitors in a variety of tissues during mouse embryogenesis. To establish a genetic tool for cell-lineage tracing and genefunction analysis, we generated mice in which the CreERT2 gene was targeted to the endogenous mouse Sox9 locus. In Sox9CreERT2/+;R26R embryos, tamoxifen activated Cre recombinase exclusively in Sox9-expressing tissues. To determine the suitability of this mouse line for developmental stage-specific gene recombination, we investigated the cellular origins of the cruciate ligaments of the knee joint and the limb tendons, in which precursor cells have not been defined. The cells in these tissues were labeled after tamoxifen treatment before or at the stage of chondrogenic mesenchymal condensation, indicating that ligament and tendon cells originated from Sox9-expressing cells and that cell fate determination occurred at mesenchymal condensation. This mouse line is a valuable tool for the temporal genetic tracing of the progeny of, and inducible gene modification in Sox9-expressing cells. genesis 48:635–644, 2010.
PMCID: PMC3982414  PMID: 20806356
Sox9; CreERT2; cell fate; cruciate ligament; limb tendon
11.  Generation and Characterization of Osterix-Cherry Reporter Mice 
Genesis (New York, N.Y. : 2000)  2012;51(4):246-258.
Osterix is a zinc finger containing transcription factor, which functions as a key regulator of osteoblast differentiation. To better understand the temporal and spatial expression of Osterix during embryonic development and in the adult skeleton, we generated Osterix-Cherry reporter mice. Bacterial recombination techniques were employed to engineer a transgenic construct, which consisted of a ~39kb DNA fragment encompassing the Osterix/Sp7 gene, but excluding adjacent gene sequences. Osterix reporter expression was characterized at embryonic, neonatal, and adult ages both by itself and in the context of a cross with Bone Sialoprotein (BSP)-Topaz reporter mice. Relative to Osterix, BSP is a more mature marker of osteoblast differentiation. In agreement with osteoblast lineage maturation, Osterix reporter expression preceded BSP reporter expression during embryonic development and spatially appeared in a much broader cell population. Strong Osterix reporter expression was observed in mature osteoblasts and osteocytes. However, weaker Osterix-Cherry positive cells were also observed in the bone marrow, possibly identifying an early osteoprogenitor cell population. Evaluation of Osterix reporter expression in male femur tissue sections from 10 days to 12 weeks of age revealed persistent expression in cells of the osteoblast lineage and a surprising increase in maturing chondrocytes of the growth plate. Also, Osterix reporter expression was transiently detected in the kidney after birth.
PMCID: PMC3602345  PMID: 23180553
osteoblast; bone; fluorescent; transgenic
12.  Conditional and Domain Specific Inactivation of the Tsc2 Gene in Neural Progenitor Cells 
Genesis (New York, N.Y. : 2000)  2013;51(4):284-292.
Tuberous sclerosis complex (TSC) is a genetic disease characterized by multiorgan benign tumors as well as neurological manifestations. Epilepsy and autism are two of the more prevalent neurological complications and are usually severe. TSC is caused by mutations in either the TSC1 (encodes hamartin) or TSC2 (encodes tuberin) genes with TSC2 mutations being associated with worse outcomes. Tuberin contains a highly conserved GTPase activating protein (GAP) domain that indirectly inhibits mammalian target of rapamycin complex 1 (mTORC1). mTORC1 dysregulation is currently thought to cause much of the pathogenesis in TSC but mTORC1-independent mechanisms may also contribute. We generated a novel conditional allele of Tsc2 by flanking exons 36 and 37 with loxP sites. Mice homozygous for this knock-in Tsc2 allele are viable and fertile with normal appearing growth and development. Exposure to Cre recombinase then creates an in-frame deletion involving critical residues of the GAP domain. Homozygous conditional mutant mice generated using Emx1Cre have increased cortical mTORC1 signaling, severe developmental brain anomalies, seizures and die within three weeks. We found normal levels of the mutant Tsc2 mRNA though GAP-deficient tuberin protein appears unstable and rapidly degraded. This novel animal model will allow further study of tuberin function including the requirement of the GAP domain for protein stability.
PMCID: PMC3633697  PMID: 23359422
cortical development; mTORC1; mTORC2; rapamycin; Tuberous Sclerosis Complex
13.  Anatomy of a blastocyst: cell behaviors driving cell fate choice and morphogenesis in the early mouse embryo 
Genesis (New York, N.Y. : 2000)  2013;51(4):219-233.
The preimplantation period of mouse early embryonic development is devoted to the specification of two extra-embryonic tissues and their spatial segregation from the pluripotent epiblast. During this period two cell fate decisions are made while cells gradually lose their totipotency. The first fate decision involves the segregation of the extra-embryonic trophectoderm (TE) lineage from the inner cell mass (ICM); the second occurs within the ICM and involves the segregation of the extra-embryonic primitive endoderm (PrE) lineage from the pluripotent epiblast (EPI) lineage, which eventually gives rise to the embryo proper. Multiple determinants, such as differential cellular properties, signaling cues and the activity of transcriptional regulators, influence lineage choice in the early embryo. Here, we provide an overview of our current understanding of the mechanisms governing these cell fate decisions ensuring proper lineage allocation and segregation, while at the same time providing the embryo with an inherent flexibility to adjust when perturbed.
PMCID: PMC3633705  PMID: 23349011
mouse embryo; preimplantation; morula; blastocyst; inner cell mass; epiblast; trophectoderm; primitive endoderm; cell lineage commitment
14.  GABAergic neurons regulate lateral ventricular development via transcription factor Pax5 
Genesis (New York, N.Y. : 2000)  2013;51(4):234-245.
Postmortem studies have revealed a downregulation of the transcription factor Pax5 in GABAergic neurons in bipolar disorder, a neurodevelopmental disorder, raising the question whether Pax5 in GABAergic neurons has a role in normal brain development. In a genetic approach to study functions of Pax5 in GABAergic neurons, Pax5 was specifically deleted in GABAergic neurons from Pax5 floxed mice using a novel Gad1-Cre transgenic mouse line expressing Cre recombinase in Gad1-positive, i.e. GABAergic neurons. Surprisingly, these mice developed a marked enlargement of the lateral ventricles at approximately seven weeks of age, which was lethal within 1–2 weeks of its appearance. This hydrocephalus phenotype was observed in mice homozygous or heterozygous for the Pax5 conditional knockout, with a gene dosage-dependent penetrance. By QTL (quantitative trait loci) mapping, a 3.5 Mb segment on mouse chromosome 4 flanked by markers D4Mit237 and D4Mit214 containing approximately 92 genes including Pax5 has previously been linked to differences in lateral ventricular size. Our findings are consistent with Pax5 being a relevant gene underlying this QTL phenotype and demonstrate that Pax5 in GABAergic neurons is essential for normal ventricular development.
PMCID: PMC3740952  PMID: 23349049
paired box genes; GABA neurons; Gad1-Cre; hydrocephalus
Skeletal muscle fibers vary in contractile and metabolic properties. Four main fiber types are present in mammalian trunk and limb muscles; they are called I, IIA, IIX and IIB, ranging from slowest- to fastest-contracting. Individual muscles contain stereotyped proportions of two or more fiber types. Fiber type is determined by a combination of nerve-dependent and –independent influences, leading to formation of “homogeneous motor units” in which all branches of a single motor neuron form synapses on fibers of a single type. Fiber type composition of muscles can be altered in adulthood by multiple factors including exercise, denervation, hormones and aging. To facilitate analysis of muscle development, plasticity and innervation, we generated transgenic mouse lines in which Type I, Type IIA, and Type IIX+B fibers can be selectively labeled with distinguishable fluorophores. We demonstrate their use for motor unit reconstruction and live imaging of nerve-dependent alterations in fiber type.
PMCID: PMC3969845  PMID: 21898764
Denervation; fluorescent proteins; motor unit; myosin heavy chain; neuromuscular; parvalbumin; myosin heavy chain
16.  Generation of Aggrecan-CreERT2 knockin mice for Inducible Cre Activity in Adult Cartilage 
Genesis (New York, N.Y. : 2000)  2009;47(12):805-814.
The function of cartilage in the adult is dependent upon a host of regulatory molecules such as growth factors, extracellular matrix, enzymes, signaling molecules and transcription factors. However, germline mutations in some genes that are expressed in adult cartilage lead to embryonic or perinatal lethality. To examine the function of these and other genes postnatally, we have generated a targeted mouse by homologous recombination that “knocks in” the inducible Cre recombinase construct, CreERT2, in the 3′ untranslated region (3′UTR) of the endogenous mouse aggrecan gene (Agc1tm(IRES-creERT2)). The properties and efficiency of the inducible cre recombinase were tested by examining X-gal staining of tissues from embryos as well as growing and adult Agc1tm(IRES-creERT2)/+; Rosa 26R mice. These mice were injected with the inducer, tamoxifen, at different time points during embryonic development and postnatally up to 6 months of age. Strong X-gal staining was observed in growth plate and articular cartilage as well as the fibrocartilage of meniscus, trachea, and intervertebral discs reproducing the pattern of endogenous aggrecan gene expression. In conclusion, we have generated a mouse model in which genes implicated in cartilage degenerative diseases can be inactivated in a spatial and temporal fashion in postnatal and adult mice.
PMCID: PMC3951921  PMID: 19830818
17.  Development of Translating Ribosome Affinity Purification for Zebrafish 
Genesis (New York, N.Y. : 2000)  2013;51(3):187-192.
The regulation of transcription and translation by specific cell types is essential to generate the cellular diversity that typifies complex multicellular organisms. Tagging and purification of ribosomal proteins has been shown to be an innovative and effective means of characterizing the ribosome bound transcriptome of highly specific cell populations in vivo. To test the feasibility of using translating ribosome affinity purification (TRAP) in zebrafish, we have generated both a ubiquitous TRAP line and a melanocyte-specific TRAP line using the native zebrafish rpl10a ribosomal protein. We have demonstrated the capacity to capture mRNA transcripts bound to ribosomes, and confirmed the expected enrichment of melanocyte specific genes and depletion of non-melanocyte genes when expressing the TRAP construct with a cell specific promoter. We have also generated a generic EGFP-rpl10a Tol2 plasmid construct (Tol2-zTRAP) that can be readily modified to target any additional cell populations with characterized promoters in zebrafish.
PMCID: PMC3638809  PMID: 23281262
TRAP; polysome; capture; danio
18.  Generation of knock-in mice that express nuclear EGFP and tamoxifen-inducible Cre recombinase in the notochord from Foxa2 and T loci 
Genesis (New York, N.Y. : 2000)  2013;51(3):210-218.
The node and the notochord are important embryonic signaling centers that control embryonic pattern formation. Notochord progenitor cells present in the node and later in the posterior end of the notochord move anteriorly to the generate notochord. To understand the dynamics of cell movement during notochord development and the molecular mechanisms controlling this event, analyses of cell movements using time-lapse imaging and conditional manipulation of gene activities are required. To achieve this goal, we generated two knock-in mouse lines that simultaneously express nuclear enhanced green fluorescent protein (EGFP) and tamoxifen-inducible Cre, CreERT2, from two notochord gene loci, Foxa2 and T (Brachury). In Foxa2nEGFP-CreERT2/+ and TnEGFP-CreERT2/+ embryos, nuclei of the Foxa2 or T-expressing cells, which include the node, notochord, and endoderm (Foxa2) or wide range of posterior mesoderm (T), were labeled with EGFP at intensities that can be used for live imaging. Cre activity was also induced in cells expressing Foxa2 and T one day after tamoxifen administration. These mice are expected to be useful tools for analyzing the mechanisms of notochord development.
PMCID: PMC3632256  PMID: 23359409
node; notochord; Foxa2; T (Brachyury); dual labeling; nuclear EGFP; inducible Cre
19.  Mx1-Cre mediated Rgs12 conditional knockout mice exhibit increased bone mass phenotype 
Genesis (New York, N.Y. : 2000)  2013;51(3):201-209.
Regulators of G-protein Signaling (Rgs) proteins are the members of a multigene family of GTPase-accelerating proteins (GAP) for the Galpha subunit of heterotrimeric G-proteins. Rgs proteins play critical roles in the regulation of G protein couple receptor (GPCR) signaling in normal physiology and human diseases such as cancer, heart diseases and inflammation. Rgs12 is the largest protein of the Rgs protein family. Some in vitro studies have demonstrated that Rgs12 plays a critical role in regulating cell differentiation and migration; however its function and mechanism in vivo is largely unknown. Here, we generated a floxed Rgs12 allele (Rgs12flox/flox) in which the exon 2, containing both PDZ and PTB_PID domains of Rgs12, was flanked with two loxp sites. By using the inducible Mx1-cre and Poly I:C system to specifically delete Rgs12 at postnatal 10 days in interferon-responsive cells including monocyte and macrophage cells, we found that Rgs12 mutant mice had growth retardation with the phenotype of increased bone mass. We further found that deletion of Rgs12 reduced osteoclast numbers and had no significant effect on osteoblast formation. Thus, Rgs12flox/flox conditional mice provide a valuable tool for in vivo analysis of Rgs12 function and mechanism through time- and cell-specific deletion of Rgs12.
PMCID: PMC3908791  PMID: 23349096
Cre; loxP; FRT; conditional inactivation; Regulator of G protein signaling protein
20.  Folate modulates Hox gene controlled skeletal phenotypes 
Genesis (New York, N.Y. : 2000)  2004;39(3):155-166.
Hox genes are well known regulators of pattern formation (Capecchi, 1996; Krumlauf, 1994) and cell differentiation (Goff and Tabin, 1997; Papenbrock et al., 2000; Yueh et al., 1998) in the developing vertebrate skeleton. Although skeletal variations are not uncommon in humans (Hald et al., 1995), few mutations in human HOX genes have been described (Goodman and Scambler, 2001). If such mutations are compatible with life, there may be physiological modifiers for the manifestation of Hox gene-controlled phenotypes, masking underlying mutations. We here present evidence that the essential nutrient folate modulates genetically induced skeletal defects in Hoxd4 transgenic mice. We also show that chondrocytes require folate for growth and differentiation and that they express folate transport genes, providing evidence for a direct effect of folate on skeletal cells. To our knowledge, this is the first report of nutritional influence on Hox gene controlled phenotypes, and implicates gene-environment interactions as important modifiers of Hox gene function. Taken together, our results demonstrate a beneficial effect of folate on skeletal development that may also be relevant to disorders and variations of the human skeleton.
PMCID: PMC3938166  PMID: 15282741
21.  Tubby-RFP Balancers for Developmental Analysis: FM7c 2xTb-RFP, CyO 2xTb-RFP and TM3 2xTb-RFP 
Genesis (New York, N.Y. : 2000)  2012;50(2):119-123.
We report here the construction of Tubby-RFP balancers for the X, 2nd and 3rd chromosomes of Drosophila melanogaster. The insertion of a 2xTb-RFP transgene on the FM7c, CyO and TM3 balancer chromosomes introduces two easily scorable, dominant, developmental markers. The strong Tb phenotype is visible to the naked eye at the larval L2, L3 and pupal stages. The RFP associated with the cuticle is easily detected at all stages from late embryo to adult with the use of a fluorescence stereomicroscope. The FM7c Bar 2xTb-RFP, CyO Cy 2xTb-RFP and TM3 Sb 2xTb-RFP balancers will greatly facilitate the analysis of lethals and other developmental mutants in L2/L3 larvae and pupae, but also provide coverage of other stages beginning in late embryogenesis through to the adult.
PMCID: PMC3931234  PMID: 21913310
Tubby; DsRed; RFP; Tb; Tb1; Balancer; Drosophila
22.  Musashi1-CreERT2: A New Cre Line for Conditional Mutagenesis in Neural Stem Cells 
Genesis (New York, N.Y. : 2000)  2012;51(2):128-134.
The RNA-binding protein Musashi1 (Msi1) is one of two mammalian homologues of Drosophila Musashi, which is required for the asymmetric cell division of sensory organ precursor cells. In the mouse central nervous system (CNS) Msi1 is preferentially expressed in mitotically active progenitor cells in the ventricular zone (VZ) of the neural tube during embryonic development and in the subventricular zone (SVZ) of the postnatal brain. Previous studies showed that cells in the SVZ can contribute to long-term neurogenesis in the olfactory bulb (OB) but it remains unclear whether Msi1-expressing cells have self-renewing potential and can contribute to neurogenesis in the adult. Here we describe the generation of Msi1-CreERT2 knock-in mice and show by cell lineage tracing that Msi1-CreERT2-expressing cells mark neural stem cells (NSCs) in both the embryonic and adult brain. Msi1-CreERT2 mice thus represent a new tool in our arsenal for genetically manipulating NSCs, which will be essential for understanding the molecular mechanisms underlying neural development.
PMCID: PMC3577968  PMID: 23132814
Msi1; NSCs; SVZ; Olfactory epithelium; Knock-in mice
23.  Nkx2.2:Cre Knock-In Mouse Line: A Novel Tool for Pancreas- and CNS-Specific Gene Deletion 
Genesis (New York, N.Y. : 2000)  2013;51(12):844-851.
Nkx2.2 is a homeodomain-containing transcriptional regulator necessary for the appropriate differentiation of ventral neuronal populations in the spinal cord and hindbrain, and endocrine cell populations in the pancreas and intestine. In each tissue, Nkx2.2 inactivation leads to reciprocal cell fate alterations. To confirm the cell fate changes are due to respecification of Nkx2.2-expressing progenitors and to provide a novel tool for lineage tracing in the pancreas and CNS, we generated an Nkx2.2:Cre mouse line by knocking in a Cre-EGFP cassette into the Nkx2.2 genomic locus and inactivating endogenous Nkx2.2. The R26R-CAG-LSL-tdTomato reporter was used to monitor the specificity and efficiency of Nkx2.2:Cre activity; the tomato reporter faithfully recapitulated endogenous Nkx2.2 expression and could be detected as early as embryonic day (e) 9.25 in the developing CNS and was initiated shortly thereafter at e9.5 in the pancreas. Lineage analyses in the CNS confirmed the cell populations thought to be derived from Nkx2.2-expressing progenitor domains. Furthermore, lineage studies verified Nkx2.2 expression in the earliest pancreatic progenitors that give rise to all cell types of the pancreas; however they also revealed more robust Cre activity in the dorsal versus ventral pancreas. Thus, the Nkx2.2:Cre line provides a novel tool for gene manipulations in the CNS and pancreas. genesis 00:00-00.
PMCID: PMC3902634  PMID: 23996959
Nkx2.2; Cre-lox; CNS; pancreas; lineage
24.  Generation of a germ cell-specific mouse transgenic CHERRY reporter, Sohlh1-mCherryFlag 
Visualization of differentiating germ cells is critical to understanding the formation of primordial follicles in the ovary, and the commitment of spermatogonial stem cells to differentiation. We engineered and generated a BAC transgenic mouse line, Sohlh1-mCherryFlag (S1CF), under the direction of the native Sohlh1 promoter. Sohlh1 is a germ cell-specific gene that encodes the basic helix-loop-helix (bHLH) transcriptional regulator that is essential in oogenesis and spermatogenesis. Sohlh1 expression is unique, and is limited to perinatal and early follicle oocytes and differentiating spermatogonia. The Sohlh1-mCherryFlag transgene was engineered to fuse SOHLH1 to the red fluorescent protein CHERRY with 3-tandem-FLAG tags. S1CF animals fluoresce specifically in the oocytes of perinatal ovaries and small follicles in adult ovaries, as well as in spermatogonia, a pattern that is similar to endogenous SOHLH1. Moreover, S1CF rescued germ cell loss and infertility in both male and female Sohlh1−/− animals. The FLAG-tag on S1CF was effective for immunostaining and immunoprecipitation. The Sohlh1-mCherryFlag transgenic mouse provides a unique model to study early germ cell differentiation, as well as in vivo imaging and purification of differentiating germ cells.
PMCID: PMC3547139  PMID: 22965810
oocyte; oogenesis; spermatogonia; spermatogenesis; imaging
25.  Domain specific genetic mosaic system in the Drosophila eye 
Genetic mosaic approach is commonly employed in the Drosophila eye by completely abolishing or misexpressing a gene within a subset of cells to unravel its role during development. Classical genetic mosaic approach involves random clone generation in all developing fields. Consequently, a large sample size needs to be screened to generate and analyze clones in specific domains of the developing eye. To address domain specific functions of genes during axial patterning, we have developed a system for generating mosaic clones by combining Gal4/UAS and FLP/FRT system which will allow generation of loss-of-function as well as gain-of-function clones on the dorsal and ventral eye margins. We used the bifid-Gal4 driver to drive expression of UAS-flippase (FLP). This reagent can have multiple applications in (i) studying spatio-temporal function of a gene during dorso-ventral axis specification in the eye, (ii) analyzing genetic epistasis of genes involved in DV patterning and (iii) conducting genome wide screens in a domain specific manner.
PMCID: PMC3547150  PMID: 23109378
Drosophila eye; Dorso-ventral (DV) axis; patterning; genetic mosaic; Gal4/UAS technique; compartments

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