The transcriptional and functional properties of mouse epiblast stem cells resemble the anterior primitive streak.

Mouse epiblast stem cells (EpiSCs) can be derived from a wide range of developmental stages. To characterize and compare EpiSCs with different origins, we derived a series of EpiSC lines from pregastrula stage to late-bud-stage mouse embryos. We found that the transcriptomes of these cells are hierarchically distinct from those of the embryonic stem cells, induced pluripotent stem cells (iPSCs), and epiblast/ectoderm.

Dullard/Ctdnep1 modulates WNT signalling activity for the formation of primordial germ cells in the mouse embryo.

Dullard/Ctdnep1 is a member of the serine/threonine phosphatase family of the C-terminal domain of eukaryotic RNA polymerase II. Embryos lacking Dullard activity fail to form primordial germ cells (PGCs). In the mouse, the formation of PGCs is influenced by BMP4 and WNT3 activity.

Rhou maintains the epithelial architecture and facilitates differentiation of the foregut endoderm.

Rhou encodes a Cdc42-related atypical Rho GTPase that influences actin organization in cultured cells. In mouse embryos at early-somite to early-organogenesis stages, Rhou is expressed in the columnar endoderm epithelium lining the lateral and ventral wall of the anterior intestinal portal. During foregut development, Rhou is downregulated in regions where the epithelium acquires a multilayered morphology heralding the budding of organ primordia.

Sox17-dependent gene expression and early heart and gut development in Sox17-deficient mouse embryos.

Sox17 is a transcription factor that is required for maintenance of the definitive endoderm in mouse embryos. By expression profiling of wild-type and mutant embryos and Sox17-overexpressing hepatoma cells, we identified genes with Sox17-dependent expression. Among the genes that were up-regulated in Sox17-null embryos and down-regulated by Sox17 expressing HepG2 cells is a set of genes that are expressed in the developing liver, suggesting that one function of Sox17 is the repression of liver gene expression, which is compatible with a role for Sox17 in maintaining the definitive endoderm in a progenitor state.

Stringent requirement of a proper level of canonical WNT signalling activity for head formation in mouse embryo.

In mouse embryos, loss of Dickkopf-1 (DKK1) activity is associated with an ectopic activation of WNT signalling responses in the precursors of the craniofacial structures and leads to a complete truncation of the head at early organogenesis. Here, we show that ENU-induced mutations of genes coding for two WNT canonical pathway factors, the co-receptor LRP6 and the transcriptional co-activator β-catenin, also elicit an ectopic signalling response and result in loss of the rostral tissues of the forebrain. Compound mutant embryos harbouring combinations of mutant alleles of Lrp6, Ctnnb1 and Dkk1 recapitulate the partial to complete head truncation phenotype of individual homozygous mutants.

Loss of Lhx1 activity impacts on the localization of primordial germ cells in the mouse.

Mouse embryos lacking Lhx1 (Lim1) activity display defective gastrulation and are deficient of primordial germ cells (PGCs) (Tsang et al. [2001] International Journal of Developmental Biology 45:549-555). To dissect the specific role of Lhx1 in germ cell development, we studied embryos with conditional inactivation of Lhx1 activity in epiblast derivatives, which, in contrast to completely null embryos, develop normally through gastrulation before manifesting a head truncation phenotype.

Dkk1 and Wnt3 interact to control head morphogenesis in the mouse.

Loss of Dkk1 results in ectopic WNT/beta-catenin signalling activity in the anterior germ layer tissues and impairs cell movement in the endoderm of the mouse gastrula. The juxtaposition of the expression domains of Dkk1 and Wnt3 is suggestive of an antagonist-agonist interaction. The downregulation of Dkk1 when Wnt3 activity is reduced reveals a feedback mechanism for regulating WNT signalling.

Gene expression pattern and progression of embryogenesis in the immediate post-implantation period of mouse development.

During development of the mouse conceptus from implantation to the early gastrula stage, a multitude of genes encoding structural proteins, transcription factors and components of signalling pathways are expressed in the extraembryonic and embryonic tissues derived from the trophectoderm and the inner cell mass. Some genes are expressed widely in the extraembryonic ectoderm, the visceral endoderm or the epiblast, while others display more restricted expression domains in these tissues or are expressed upon the specification of the germ layers at gastrulation. Overall, the developmental changes in gene expression mirror key events of embryogenesis, and reveal the regionalization of signalling activity and the emergence of tissue patterning.

Expression analysis of the Epha1 receptor tyrosine kinase and its high-affinity ligands Efna1 and Efna3 during early mouse development.

Interaction of Eph receptor tyrosine kinases with their membrane bound ephrin ligands initiates bidirectional signaling events that regulate cell migratory and adhesive behavior. Whole-mount in situ hybridization revealed overlapping expression of the Epha1 receptor and its high-affinity ligands ephrin A1 (Efna1) and ephrin A3 (Efna3) in the primitive streak and the posterior paraxial mesoderm during early mouse development. These results show complex and dynamic expression for all three genes with expression domains that are successively complementary, overlapping, and divergent.

Conserved requirement of Lim1 function for cell movements during gastrulation.

To investigate Lim1 function during gastrulation, we used transcript depletion through DEED antisense oligonucleotides in Xenopus and cell transplantation in mice. Xenopus embryos depleted of Lim1 lack anterior head structures and fail to form a proper axis as a result of a failure of gastrulation movements, even though mesodermal cell identities are specified. Similar disruption of cell movements in the mesoderm is also observed in Lim1(-/-) mice.

Isolation of differentially expressed genes from wild-type and Twist mutant mouse limb buds.

In the mouse, Twist is required for normal limb and craniofacial development. We show that the aristaless-like transcription factors, Alx3 and Alx4 are downregulated in the Twist(-/-) mutant and may be potential targets of Twist. By suppression subtractive hybridization we isolated 31 and 18 unique clones representing mRNAs that are putatively downregulated and upregulated respectively in Twist(-/-) forelimb buds.

Twist function is required for the morphogenesis of the cephalic neural tube and the differentiation of the cranial neural crest cells in the mouse embryo.

Loss of Twist function in the cranial mesenchyme of the mouse embryo causes failure of closure of the cephalic neural tube and malformation of the branchial arches. In the Twist(-/-) embryo, the expression of molecular markers that signify dorsal forebrain tissues is either absent or reduced, but those associated with ventral tissues display expanded domains of expression. Dorsoventral organization of the mid- and hindbrain and the anterior-posterior pattern of the neural tube are not affected.