Project description:A conserved molecular pathway has emerged controlling endoderm formation in Xenopus zebrafish and mice. Key genes in this pathway include Nodal ligands and transcription factors of the Mix-like paired homeodomain class, Gata4-6 zinc finger factors and Sox17 HMG domain proteins. While a linear epistatic pathway has been proposed, the precise hierarchical relationships between these factors and their downstream targets are largely unresolved. Here we used a combination of microarray analysis and loss-of-function experiments to examine the global regulatory network controlling Xenopus endoderm formation. We identified over 300 transcripts enriched in the gastrula endoderm, including most of the known endoderm regulators as well as over a hundred uncharacterized genes. Surprisingly only 10% of the endoderm transcriptome is regulated as predicted by the current linear model. We find that Nodals, Mixer and Sox17 have both shared and distinct sets of downstream targets and that a number of unexpected autoregulatory loops exist between Sox17 and Gata4-6, Sox17 and Bix1, 2, 4 and between Sox17 and Xnr4. We find that Mixer does not function primarily via Sox17 as previously proposed. This data provides a new insight into the complexity of endoderm formation and will serve as valuable resource for establishing a complete endoderm gene regulatory network. Experiment Overall Design: Define a set of transcripts with enriched expression in the gastrula endoderm of the Xenopus laevis embryo and determine how these are regulated by nodal signaling, Mixer and Sox17 using loss-of-function experiments. For more specific details see Sinner et al., (2006) Global analysis of the transcriptional network controlling Xenopus endoderm formation.
Project description:A conserved molecular pathway has emerged controlling endoderm formation in Xenopus zebrafish and mice. Key genes in this pathway include Nodal ligands and transcription factors of the Mix-like paired homeodomain class, Gata4-6 zinc finger factors and Sox17 HMG domain proteins. While a linear epistatic pathway has been proposed, the precise hierarchical relationships between these factors and their downstream targets are largely unresolved. Here we used a combination of microarray analysis and loss-of-function experiments to examine the global regulatory network controlling Xenopus endoderm formation. We identified over 300 transcripts enriched in the gastrula endoderm, including most of the known endoderm regulators as well as over a hundred uncharacterized genes. Surprisingly only 10% of the endoderm transcriptome is regulated as predicted by the current linear model. We find that Nodals, Mixer and Sox17 have both shared and distinct sets of downstream targets and that a number of unexpected autoregulatory loops exist between Sox17 and Gata4-6, Sox17 and Bix1, 2, 4 and between Sox17 and Xnr4. We find that Mixer does not function primarily via Sox17 as previously proposed. This data provides a new insight into the complexity of endoderm formation and will serve as valuable resource for establishing a complete endoderm gene regulatory network. Keywords: Embryonic, Development. Endoderm, Xenopus, nodal, Sox17, Mixer, microarray, gene regulatory network
Project description:Retinoic acid (RA) is required for pancreas specification in Xenopus and other vertebrates. However, the gene network that is directly induced by RA-signalling in this context remains to be defined. We identified the transcription factor Hnf1β and the Wnt-receptor Fzd4/Fzd4s as direct RA-target genes through RNA-sequencing of in vitro generated pancreatic explants. Functional analyses of Hnf1β and Fzd4/Fzd4s in programmed pancreatic explants and whole embryos revealed their requirement for pancreatic progenitor formation and differentiation. Hnf1β and Fzd4/Fzd4s thus appear to be involved in pre-patterning events of the embryonic endoderm allowing for pancreas formation.
Project description:The transcription factors Mixer and Sox17beta have well characterized roles in endoderm specification during Xenopus embryogenesis. In order to more thoroughly understand the mechanisms by which these endodermal regulators act, we expressed Mixer and Sox17beta in naïve ectodermal tissue and, using oligonucleotide-based microarrays, compared their genomic transcriptional profile to that of unaffected tissue. Using this novel approach, we identified 71 transcripts that are upregulated by Mixer or Sox17beta, 63 of which have previously uncharacterized roles in endoderm development. Furthermore, an in situ hybridization screen using antisense probes for several of these clones identified six targets of Mixer and/or Sox17beta that are expressed in the endoderm during gastrula stages, providing new and regional markers of the endoderm. Our results contribute further insight into the functions of Mixer and Sox17beta and bring us closer to understanding at the molecular level the pathways that regulate endoderm development.