Abstract
BackgroundNodal signalling is an absolute requirement for normal mesoderm and endoderm formation in vertebrate embryos, yet the transcriptional networks acting directly downstream of Nodal and the extent to which they are conserved is largely unexplored, particularly in vivo. Eomesodermin also plays a role in patterning mesoderm and endoderm in vertebrates, but its mechanisms of action and how it interacts with the Nodal signalling pathway are still unclear.ResultsUsing a combination of expression analysis and chromatin immunoprecipitation with deep sequencing (ChIP-seq) we identify direct targets of Smad2, the effector of Nodal signalling in blastula stage zebrafish embryos, including many novel target genes. Through comparison of these data with published ChIP-seq data in human, mouse and Xenopus we show that the transcriptional network driven by Smad2 in mesoderm and endoderm is conserved in these vertebrate species. We also show that Smad2 and zebrafish Eomesodermin a (Eomesa) bind common genomic regions proximal to genes involved in mesoderm and endoderm formation, suggesting Eomesa forms a general component of the Smad2 signalling complex in zebrafish. Combinatorial perturbation of Eomesa and Smad2-interacting factor Foxh1 results in loss of both mesoderm and endoderm markers, confirming the role of Eomesa in endoderm formation and its functional interaction with Foxh1 for correct Nodal signalling. Finally, we uncover a novel role for Eomesa in repressing ectodermal genes in the early blastula.ConclusionsOur data demonstrate that evolutionarily conserved developmental functions of Nodal signalling occur through maintenance of the transcriptional network directed by Smad2. This network is modulated by Eomesa in zebrafish which acts to promote mesoderm and endoderm formation in combination with Nodal signalling, whilst Eomesa also opposes ectoderm gene expression. Eomesa, therefore, regulates the formation of all three germ layers in the early zebrafish embryo.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-014-0081-5) contains supplementary material, which is available to authorized users.
Highlights
Nodal signalling is an absolute requirement for normal mesoderm and endoderm formation in vertebrate embryos, yet the transcriptional networks acting directly downstream of Nodal and the extent to which they are conserved is largely unexplored, in vivo
Our analysis revealed a set of genes downregulated on ndr1 injection that are significantly associated with lone Eomesodermin a (Eomesa) genomic binding (Figure 3H), which are enriched for known expression in neural structures
Their study used a dominant negative eomesa in the context of a foxh1 mutant, and suggested that the two factors together regulate the entirety of Nodal signaling in early development
Summary
Nodal signalling is an absolute requirement for normal mesoderm and endoderm formation in vertebrate embryos, yet the transcriptional networks acting directly downstream of Nodal and the extent to which they are conserved is largely unexplored, in vivo. Nodal signalling acts through ligandmediated receptor activation of the transcription factors Smad2/3 On pathway activation these factors translocate to the nucleus where they interact with other transcription factors at genomic cis-regulatory elements to modulate target gene expression [2], leading to induction of mesoderm and endoderm, ventral neural tube formation and establishment of bilateral asymmetry [3]. The importance of this pathway in early development is seen in loss of Nodal signalling mutants in mouse and zebrafish, which display perturbed mesoderm, endoderm and ventral neural tube formation (for example, [4,5,6,7,8]). The extent to which the transcriptional networks directed by Smad are evolutionarily maintained has not been determined
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
