Differential regulation of epiboly initiation and progression by zebrafish Eomesodermin A

Du S, Draper BW, Mione M, Moens CB, Bruce A

Dev. Biol. 2012 Feb;362(1):11-23

PMID: 22142964


The T-box transcription factor Eomesodermin (Eomes) has been implicated in patterning and morphogenesis in frog, fish and mouse. In zebrafish, one of the two Eomes homologs, Eomesa, has been implicated in dorsal-ventral patterning, epiboly and endoderm specification in experiments employing over-expression, dominant-negative constructs and antisense morpholino oligonucleotides. Here we report for the first time the identification and characterization of an Eomesa mutant generated by TILLING. We find that Eomesa has a strictly maternal role in the initiation of epiboly, which involves doming of the yolk cell up into the overlying blastoderm. By contrast, epiboly progression is normal, demonstrating for the first time that epiboly initiation is genetically separable from progression. The yolk cell microtubules, which are required for epiboly, are defective in maternal-zygotic eomesa mutant embryos. In addition, the deep cells of the blastoderm are more tightly packed and exhibit more bleb-like protrusions than cells in control embryos. We postulate that the doming delay may be the consequence both of overly stabilized yolk cell microtubules and defects in the adhesive properties or motility of deep cells. We also show that Eomesa is required for normal expression of the endoderm markers sox32, bon and og9x; however it is not essential for endoderm formation.

Comparative analyses of C4 and C3 photosynthesis in developing leaves of maize and rice

Wang L, Czedik-Eysenberg A, Mertz RA, Si Y, Tohge T, Nunes-Nesi A, Arrivault S, Dedow LK, Bryant DW, Zhou W, Xu J, Weissmann S, Studer A, Li P, Zhang C, LaRue T, Shao Y, Ding Z, Sun Q, Patel RV, Turgeon R, Zhu X, Provart NJ, Mockler TC, Fernie AR, Stitt M, Liu P, Brutnell TP

Nat. Biotechnol. 2014 Oct;

PMID: 25306245


C4 and C3 photosynthesis differ in the efficiency with which they consume water and nitrogen. Engineering traits of the more efficient C4 photosynthesis into C3 crops could substantially increase crop yields in hot, arid conditions. To identify differences between C4 and C3 photosynthetic mechanisms, we profiled metabolites and gene expression in the developing leaves of Zea mays (maize), a C4 plant, and Oryza sativa (rice), a C3 plant, using a statistical method named the unified developmental model (UDM). Candidate cis-regulatory elements and transcription factors that might regulate photosynthesis were identified, together with differences between C4 and C3 nitrogen and carbon metabolism. The UDM algorithms could be applied to analyze and compare development in other species. These data sets together with community viewers to access and mine them provide a resource for photosynthetic research that will inform efforts to engineer improvements in carbon fixation in economically valuable grass crops.

Global identification of Smad2 and Eomesodermin targets in zebrafish identifies a conserved transcriptional network in mesendoderm and a novel role for Eomesodermin in repression of ectodermal gene expression

Nelson AC, Cutty SJ, Niini M, Stemple DL, Flicek P, Houart C, Bruce A, Wardle FC

BMC Biol. 2014 Oct;12(1):81

PMID: 25277163


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 ChIP-seq and expression analysis 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.ConclusionOur 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.