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Janet Rossant

Publications and source records attributed to Janet Rossant.

At least 37 records · Page 2Linked to original sources
PubMed2006

Mouse trophoblast stem cells.

The trophectoderm is one of the earliest cell types to differentiate in the forming mammalian embryo. It is responsible for the initial implantation and the formation of the trophoblast components of the placenta, an organ essential for nutrient and waste exchange between the fetus and its mother. The trophoblast can be modeled in vitro using trophoblast stem cells. Trophoblast stem cells require fibroblast growth factor (FGF)4, heparin, and contact with embryonic fibroblasts, or fibroblast-conditioned medium. They grow as tight epithelial colonies, which express markers of the early trophectoderm and have been shown to contribute to all of the components of the placenta through chimera studies. These cells can be passaged indefinitely and can be differentiated by removal of FGF4 and fibroblasts and will express genetic markers of later placental cell types. This chapter will discuss the initial derivation of trophoblast stem cells from the blastocyst stage, maintenance, differentiation, flow cytometry and transfection techniques that can be used with these cells.

Animals↗
PubMed2005

Endothelial cells and VEGF in vascular development.

The intricate patterning processes that establish the complex vascular system during development depend on a combination of intrinsic pre-patterning and extrinsic responses to environmental parameters. Mutational studies in mice and fish have shown that the vascular system is highly sensitive to genetic disruption and have identified potential targets for therapeutic interventions. New insights into non-vascular roles of vascular endothelial growth factor and the requirement for endothelial cells in adult organs and stem-cell niches highlight possible side effects of anti-angiogenic therapy and the need for new targets.

Animals↗
PubMed2005

Interaction between Oct3/4 and Cdx2 determines trophectoderm differentiation.

Trophectoderm (TE), the first differentiated cell lineage of mammalian embryogenesis, forms the placenta, a structure unique to mammalian development. The differentiation of TE is a hallmark event in early mammalian development, but molecular mechanisms underlying this first differentiation event remain obscure. Embryonic stem (ES) cells can be induced to differentiate into the TE lineage by forced repression of the POU-family transcription factor, Oct3/4. We show here that this event can be mimicked by overexpression of Caudal-related homeobox 2 (Cdx2), which is sufficient to generate proper trophoblast stem (TS) cells. Cdx2 is dispensable for trophectoderm differentiation induced by Oct3/4 repression but essential for TS cell self-renewal. In preimplantation embryos, Cdx2 is initially coexpressed with Oct3/4 and they form a complex for the reciprocal repression of their target genes in ES cells. This suggests that reciprocal inhibition between lineage-specific transcription factors might be involved in the first differentiation event of mammalian development.

Animals↗
PubMed2005

Deletion of the selection cassette, but not cis-acting elements, in targeted Flk1-lacZ allele reveals Flk1 expression in multipotent mesodermal progenitors.

Flk1, the gene encoding the vascular endothelial growth factor receptor 2 (VEGFR-2), is a well-known marker for vascular and hematopoietic progenitors and is indispensable for normal hematopoiesis and vasculogenesis. Here we show that Flk1 expression in the early mouse embryo marks a broad spectrum of mesodermal progenitors exiting the primitive streak as well as later mesodermal cell types including some cardiomyocytes, portions of the somites, and all extraembryonic mesoderm cells. These findings made use of an Flk1-lacZ knock-in allele in which the neomycin selection cassette was removed, which resulted in full replication of the endogenous expression of Flk1. Targeted deletion of a region in intron 1 that has been proposed to direct endothelial expression produced no alteration in either endothelial or broader mesodermal expression of the Flk1-lacZ allele. Examination of lacZ expression in homozygotes for the Flk1lacZ neo-out allele revealed that lacZ-expressing mesodermal cells persisted in nonvascular regions. Thus, Flk1 expression marks progenitors with broad mesodermal potential but is not absolutely required for the development of all mesodermal lineages in which it is expressed.

Alleles↗
PubMed2005

Genome-wide analysis of mouse transcripts using exon microarrays and factor graphs.

Recent mammalian microarray experiments detected widespread transcription and indicated that there may be many undiscovered multiple-exon protein-coding genes. To explore this possibility, we labeled cDNA from unamplified, polyadenylation-selected RNA samples from 37 mouse tissues to microarrays encompassing 1.14 million exon probes. We analyzed these data using GenRate, a Bayesian algorithm that uses a genome-wide scoring function in a factor graph to infer genes. At a stringent exon false detection rate of 2.7%, GenRate detected 12,145 gene-length transcripts and confirmed 81% of the 10,000 most highly expressed known genes. Notably, our analysis showed that most of the 155,839 exons detected by GenRate were associated with known genes, providing microarray-based evidence that most multiple-exon genes have already been identified. GenRate also detected tens of thousands of potential new exons and reconciled discrepancies in current cDNA databases by 'stitching' new transcribed regions into previously annotated genes.

Algorithms↗
PubMed2005

Dissecting Wnt/beta-catenin signaling during gastrulation using RNA interference in mouse embryos.

Differential gene regulation integrated in time and space drives developmental programs during embryogenesis. To understand how the program of gastrulation is regulated by Wnt/beta-catenin signaling, we have used genome-wide expression profiling of conditional beta-catenin mutant embryos. Known Wnt/beta-catenin target genes, known components of other signaling pathways, as well as a number of uncharacterized genes were downregulated in these mutants. To further narrow down the set of differentially expressed genes, we used whole-mount in situ screening to associate gene expression with putative domains of Wnt activity. Several potential novel target genes were identified by this means and two, Grsf1 and Fragilis2, were functionally analyzed by RNA interference (RNAi) in completely embryonic stem (ES) cell-derived embryos. We show that the gene encoding the RNA-binding factor Grsf1 is important for axial elongation, mid/hindbrain development and axial mesoderm specification, and that Fragilis2, encoding a transmembrane protein, regulates epithelialization of the somites and paraxial mesoderm formation. Intriguingly, the knock-down phenotypes recapitulate several aspects of Wnt pathway mutants, suggesting that these genes are components of the downstream Wnt response. This functional genomic approach allows the rapid identification of functionally important components of embryonic development from large datasets of putative targets.

Alkaline Phosphatase↗
PubMed2005

Cdx2 is required for correct cell fate specification and differentiation of trophectoderm in the mouse blastocyst.

Blastocyst formation marks the segregation of the first two cell lineages in the mammalian preimplantation embryo: the inner cell mass (ICM) that will form the embryo proper and the trophectoderm (TE) that gives rise to the trophoblast lineage. Commitment to ICM lineage is attributed to the function of the two transcription factors, Oct4 (encoded by Pou5f1) and Nanog. However, a positive regulator of TE cell fate has not been described. The T-box protein eomesodermin (Eomes) and the caudal-type homeodomain protein Cdx2 are expressed in the TE, and both Eomes and Cdx2 homozygous mutant embryos die around the time of implantation. A block in early TE differentiation occurs in Eomes mutant blastocysts. However, Eomes mutant blastocysts implant, and Cdx2 and Oct4 expression are correctly restricted to the ICM TE. Blastocoel formation initiates in Cdx2 mutants but epithelial integrity is not maintained and embryos fail to implant. Loss of Cdx2 results in failure to downregulate Oct4 and Nanog in outer cells of the blastocyst and subsequent death of those cells. Thus, Cdx2 is essential for segregation of the ICM and TE lineages at the blastocyst stage by ensuring repression of Oct4 and Nanog in the TE.

Animals↗
PubMed2005

Magnetic resonance imaging for detection and analysis of mouse phenotypes.

With the enormous and growing number of experimental and genetic mouse models of human disease, there is a need for efficient means of characterizing abnormalities in mouse anatomy and physiology. Adaptation of magnetic resonance imaging (MRI) to the scale of the mouse promises to address this challenge and make major contributions to biomedical research by non-invasive assessment in the mouse. MRI is already emerging as an enabling technology providing informative and meaningful measures in a range of mouse models. In this review, recent progress in both in vivo and post mortem imaging is reported. Challenges unique to mouse MRI are also identified. In particular, the needs for high-throughput imaging and comparative anatomical analyses in large biological studies are described and current efforts at handling these issues are presented.

Animals↗
PubMed2005

Two mouse mutations mapped to chromosome 11 with differing morphologies but similar progressive inflammatory alopecia.

Alopecia is a common dermatological condition in humans and other mammals. Here, we present two similar but histologically distinct mouse models of scarring alopecia. Both mutant lines were generated using random genome-wide N-ethyl-N-nitrosourea mutagenesis, and both harbor dominant mutations on chromosome 11. In both mutants, there is an early onset of alopecia that progresses to nearly complete pelage hair loss in both males and females by 20 weeks of age. Histologically, there is an increased dermal cellularity due to inflammatory cell infiltration at 7-10 days of age. By 3 weeks of age, the epidermis is acanthotic and the dermis is approximately twice as thick as in control mice due to a substantial, mostly mononuclear, inflammatory cell infiltrate. This infiltrate becomes more perifollicular by 4-5 weeks of age but is localized differently in the two mutants. In alopecia 1 (Alo-1), the perifollicular infiltrate is confined to the portion of the follicle within the dermis, whereas in Alo-2, the infiltrate extends the full length of the follicle. Expression of major histocompatibility complex (MHC) class I on the follicular epithelium in the two mutants is much greater than that in non-mutants. Furthermore, MHC class I expression is localized differently in the two mutant lines and mirrors the pattern of the inflammatory infiltrate. Despite these differences, the clinical progression of alopecia is identical in both mutants. The early onset of the disease, predictable progression, and differences in inflammatory cell localization between the two mutants make these mice particularly useful models for inflammatory hair loss and autoimmune diseases in general.

Alopecia↗
PubMed2005

Imprinted X-inactivation in extra-embryonic endoderm cell lines from mouse blastocysts.

The extra-embryonic endoderm lineage plays a major role in the nutritive support of the embryo and is required for several inductive events, such as anterior patterning and blood island formation. Blastocyst-derived embryonic stem (ES) and trophoblast stem (TS) cell lines provide good models with which to study the development of the epiblast and trophoblast lineages, respectively. We describe the derivation and characterization of cell lines that are representative of the third lineage of the blastocyst -extra-embryonic endoderm. Extra-embryonic endoderm (XEN) cell lines can be reproducibly derived from mouse blastocysts and passaged without any evidence of senescence. XEN cells express markers typical of extra-embryonic endoderm derivatives, but not those of the epiblast or trophoblast. Chimeras generated by injection of XEN cells into blastocysts showed exclusive contribution to extra-embryonic endoderm cell types. We used female XEN cells to investigate the mechanism of X chromosome inactivation in this lineage. We observed paternally imprinted X-inactivation, consistent with observations in vivo. Based on gene expression analysis, chimera studies and imprinted X-inactivation, XEN cell lines are representative of extra-embryonic endoderm and provide a new cell culture model of an early mammalian lineage.

Animals↗
PubMed2005

A Gja1 missense mutation in a mouse model of oculodentodigital dysplasia.

Oculodentodigital dysplasia (ODDD) is an autosomal dominant disorder characterized by pleiotropic developmental anomalies of the limbs, teeth, face and eyes that was shown recently to be caused by mutations in the gap junction protein alpha 1 gene (GJA1), encoding connexin 43 (Cx43). In the course of performing an N-ethyl-N-nitrosourea mutagenesis screen, we identified a dominant mouse mutation that exhibits many classic symptoms of ODDD, including syndactyly, enamel hypoplasia, craniofacial anomalies and cardiac dysfunction. Positional cloning revealed that these mice carry a point mutation in Gja1 leading to the substitution of a highly conserved amino acid (G60S) in Cx43. In vivo and in vitro studies revealed that the mutant Cx43 protein acts in a dominant-negative fashion to disrupt gap junction assembly and function. In addition to the classic features of ODDD, these mutant mice also showed decreased bone mass and mechanical strength, as well as altered hematopoietic stem cell and progenitor populations. Thus, these mice represent an experimental model with which to explore the clinical manifestations of ODDD and to evaluate potential intervention strategies.

Abnormalities, Multiple↗
PubMed2004

The functional landscape of mouse gene expression.

BACKGROUND: Large-scale quantitative analysis of transcriptional co-expression has been used to dissect regulatory networks and to predict the functions of new genes discovered by genome sequencing in model organisms such as yeast. Although the idea that tissue-specific expression is indicative of gene function in mammals is widely accepted, it has not been objectively tested nor compared with the related but distinct strategy of correlating gene co-expression as a means to predict gene function. RESULTS: We generated microarray expression data for nearly 40,000 known and predicted mRNAs in 55 mouse tissues, using custom-built oligonucleotide arrays. We show that quantitative transcriptional co-expression is a powerful predictor of gene function. Hundreds of functional categories, as defined by Gene Ontology 'Biological Processes', are associated with characteristic expression patterns across all tissues, including categories that bear no overt relationship to the tissue of origin. In contrast, simple tissue-specific restriction of expression is a poor predictor of which genes are in which functional categories. As an example, the highly conserved mouse gene PWP1 is widely expressed across different tissues but is co-expressed with many RNA-processing genes; we show that the uncharacterized yeast homolog of PWP1 is required for rRNA biogenesis. CONCLUSIONS: We conclude that 'functional genomics' strategies based on quantitative transcriptional co-expression will be as fruitful in mammals as they have been in simpler organisms, and that transcriptional control of mammalian physiology is more modular than is generally appreciated. Our data and analyses provide a public resource for mammalian functional genomics.

Animals↗
PubMed2004

Baf60c is essential for function of BAF chromatin remodelling complexes in heart development.

Tissue-specific transcription factors regulate several important aspects of embryonic development. They must function in the context of DNA assembled into the higher-order structure of chromatin. Enzymatic complexes such as the Swi/Snf-like BAF complexes remodel chromatin to allow the transcriptional machinery access to gene regulatory elements. Here we show that Smarcd3, encoding Baf60c, a subunit of the BAF complexes, is expressed specifically in the heart and somites in the early mouse embryo. Smarcd3 silencing by RNA interference in mouse embryos derived from embryonic stem cells causes defects in heart morphogenesis that reflect impaired expansion of the anterior/secondary heart field, and also results in abnormal cardiac and skeletal muscle differentiation. An intermediate reduction in Smarcd3 expression leads to defects in outflow tract remodelling reminiscent of human congenital heart defects. Baf60c overexpressed in cell culture can mediate interactions between cardiac transcription factors and the BAF complex ATPase Brg1, thereby potentiating the activation of target genes. These results reveal tissue-specific and dose-dependent roles for Baf60c in recruiting BAF chromatin remodelling complexes to heart-specific enhancers, providing a novel mechanism to ensure transcriptional regulation during organogenesis.

Animals↗
PubMed2004

Dosage-sensitive requirement for mouse Dll4 in artery development.

Involvement of the Notch signaling pathway in vascular development has been demonstrated by both gain- and loss-of-function mutations in humans, mice, and zebrafish. In zebrafish, Notch signaling is required for arterial identity by suppressing the venous fate in developing artery cells. In mice, the Notch4 receptor and the Delta-like 4 (Dll4) ligand are specifically expressed in arterial endothelial cells, suggesting a similar role. Here we show that the Dll4 ligand alone is required in a dosage-sensitive manner for normal arterial patterning in development. This implicates Dll4 as the specific mammalian endothelial ligand for autocrine endothelial Notch signaling, and suggests that Dll4 may be a suitable target for intervention in arterial angiogenesis.

Animals↗
PubMed2004

Connexin31-deficient trophoblast stem cells: a model to analyze the role of gap junction communication in mouse placental development.

The connexin (Cx) expression during placental development in rodents is subject to exacting spatiotemporal regulation. Following implantation, Cx31 characterizes the early trophoblast cell lineage and is expressed by the spongiotrophoblast during placental development until birth. Inactivation of the Cx31 gene results in a transient placental dysmorphogenesis with an imbalance in the trophoblast cell lineage differentiation in favor to giant cells [Dev. Biol. 231 (2001) 334]. In this study, we show that trophoblast stem (TS) cells exhibit the same connexin expression found in trophoblast cell lineage differentiation. Undifferentiated TS cells exclusively express Cx31 protein and Cx31.1 transcripts. Upon differentiation of TS cells, placental-specific Cx26 and Cx43 are induced. Cx31 knockout TS cells revealed an accelerated differentiation process to giant cells compared to controls, indicated by an overall shift in expression of connexins and marker genes such as Mash2, Pl-1, and Tpbpa. Moreover, proliferation was significantly reduced in Cx31 knockout TS cells upon differentiation. Both wild type and Cx31 knockout TS cells are able to invade and erode host vessels when injected into nude mice. We conclude that during trophoblast cell lineage differentiation, the Cx31 gap junction channel is involved in maintaining the proliferative diploid trophoblast cell population.

Animals↗
PubMed2004

The mouse homeobox gene Not is required for caudal notochord development and affected by the truncate mutation.

The floating head (flh) gene in zebrafish encodes a homeodomain protein, which is essential for notochord formation along the entire body axis. flh orthologs, termed Not genes, have been isolated from chick and Xenopus, but no mammalian ortholog has yet been identified. Truncate (tc) is an autosomal recessive mutation in mouse that specifically disrupts the development of the caudal notochord. Here, we demonstrate that truncate arose by a mutation in the mouse Not gene. The truncate allele (Nottc) contains a point mutation in the homeobox of Not that changes a conserved Phenylalanine residue in helix 1 to a Cysteine (F20C), and significantly destabilizes the homeodomain. Reversion of F20C in one allele of homozygous tc embryonic stem (ES) cells is sufficient to restore normal notochord formation in completely ES cell-derived embryos. We have generated a targeted mutation of Not by replacing most of the Not coding sequence, including the homeobox with the eGFP gene. The phenotype of NoteGFP/eGFP, NoteGFP/tc, and Nottc/tc embryos is very similar but slightly more severe in NoteGFP/eGFP than in Nottc/tc embryos. This confirms allelism of truncate and Not, and indicates that tc is not a complete null allele. Not expression is abolished in Foxa2 and T mutant embryos, suggesting that Not acts downstream of both genes during notochord development. This is in contrast to zebrafish embryos, in which flh interacts with ntl (zebrafish T) in a regulatory loop and is essential for development of the entire notochord, and suggests that different genetic control circuits act in different vertebrate species during notochord formation.

Amino Acid Sequence↗
PubMed2004

Cdx2 is essential for axial elongation in mouse development.

Inactivation of Cdx2 leads to preimplantation embryonic lethality. Rescue of the implantation defect by tetraploid fusion established that Cdx2 is necessary for trophoblastic development, vasculogenesis in the yolk sac mesoderm, allantoic growth, and chorioallantoic fusion. "Rescued" Cdx2 mutants die at late gastrulation stages because of failure of placental development. Cdx2 is also needed for the completion of the normal process of gastrulation and tail bud elongation. Presegmental paraxial mesoderm is severely restricted in amount and somites posterior to somite 5 are abnormal. The Cdx2 mutation, like mutations impairing Wnt and Fgf signaling, causes posterior truncations and disturbs axial patterning of the embryonic structures, indicated by changes in the Hox expression domains. The gene appears to be important in the integration of the pathways controlling embryonic axial elongation, and anterior-posterior patterning.

Animals↗