Chimaeric conceptuses have been produced by injection of 5 1/2-and 6 1/2-day extra-embryonic ectoderm and 5 1/2-day embryonic and extra-embryonic endoderm into 3 1/2-day mouse blastocysts. Extra-embryonic ectoderm cells contributed only to the ectoplacental cone and/or trophoblast giant cell fractions, reflecting the probable trophectoderm origin of these cells. Proximal (visceral) endoderm cel...

The anterior visceral endoderm (AVE) plays an important role in anterior-posterior axis formation in the mouse. The AVE functions in part by expressing secreted factors that antagonize growth factor signaling in the proximal epiblast. Here we report that the Secreted frizzled-related protein 5 (Sfrp5) gene, which encodes a secreted factor that can antagonize Wnt signaling, is expressed in the A...

In the present study, we addressed the role of (beta)-catenin in the specification of embryonic cells of the ascidians Ciona intestinalis and C. savignyi and obtained the following results: (1) During cleavages, (beta)-catenin accumulated in the nuclei of vegetal blastomeres, suggesting that it plays a role in the specification of endoderm. (2) Mis- and/or overexpression of (beta)-catenin induc...

The homeobox gene Lox3 is expressed in a segmentally iterated pattern within the endoderm of the leech Helobdella. We use that expression here to study endoderm differentiation following experimental ablations of mesoderm. Lox3 RNA was first detected by in situ hybridization at the stage when a definitive cellular endoderm is formed from its syncytial precursor and was never observed in derivat...

Rana pipiens embryos at the end of the blastula stage were dissociated and the cell suspension was separated into presumptive ectoderm, mesoderm, light endoderm, and heavy endoderm cells by a discontinuous density gradient centrifugation technique. The isolated germ layers were analyzed for total lipid, lipid phosphorus, plasmalogen, RNA, and DNA. Per gram dry weight, DNA showed a threefold dec...

As the result of early specification processes, sea urchin embryos eventually form various mesodermal cell lineages and a gut consisting of fore-, mid- and hindgut. The progression of specification as well as the overall spatial organization of the organism is encoded in its gene regulatory networks (GRNs). We have analyzed the GRN driving endoderm specification up to the onset of gastrulation ...

Canonical Wnt signaling converts the TCF/LEF transcription factor from repressor to activator by increasing nuclear levels of its coactivator, beta-catenin. A striking exception had been reported for Wnt-induced endoderm formation during C. elegans embryogenesis. It has long been believed that transcriptional activation of Wnt target genes in the endoderm precursor occurred due to a lowering of...

Two regions expressing Hex in the early gastrula contribute to organizing the anterior of the vertebrate embryo. In Xenopus, these include the anterior yolky endoderm and the suprablastoporal endoderm (SBE), which is fated to form the epithelial lining of the gut. These tissues may correspond to the anterior visceral endoderm and anterior definitive endoderm of amniotes. Genetic studies in mice...

Specification of germ layers is a crucial event in early embryogenesis. In embryos of the ascidian, Halocynthia roretzi, endoderm cells originate from two distinct lineages in the vegetal hemisphere. Cell dissociation experiments suggest that cell interactions are required for posterior endoderm formation, which has hitherto been thought to be solely regulated by localized egg cytoplasmic facto...

During mouse lung morphogenesis, the distal mesenchyme regulates the growth and branching of adjacent endoderm. We report here that fibroblast growth factor 10 (Fgf10) is expressed dynamically in the mesenchyme adjacent to the distal buds from the earliest stages of lung development. The temporal and spatial pattern of gene expression suggests that Fgf10 plays a role in directional outgrowth an...