Smad2 and smad3 Are Required for Mesendoderm Induction by Transforming Growth Factor-β/Nodal Signals in Zebrafish

Ying Zheng,Xiang Li,Shunji Jia,Zhen Ren,Anming Meng

doi:10.1074/jbc.m707578200

Abstract

The transforming growth factor-beta ligands Nodal, activin, and Vg1 play important roles in mesendoderm induction and patterning during vertebrate embryogenesis. These ligands are believed to transduce the signal through the receptor-activated transcription factors Smad2 and Smad3. However, the roles of smad2/3 genes in development of zebrafish embryos are largely unknown because the presence of multiple smad2/3 genes and their maternal expression have hampered the investigation of their developmental roles. We generated potent and specific dominant-negative forms of zebrafish Smad2, Smad3a, and Smad3b by mutating multiple amino acids. Overexpression of these mutants abolished mesendoderm induction by ectopic Nodal signaling in zebrafish embryos. Expression of dominant-negative smad2/3 abrogated Smad2/3 activities in wild-type embryos and caused various mesendodermal defects similar to those in Nodal-deficient embryos. Smad2/3-deficient cells transplanted into the blastodermal margin of wild-type hosts preferentially differentiated into ectodermal tissues rather than mesendodermal tissues, supporting the idea that response of cells to mesendoderm inducers requires Smad2/3 activities. Interference with Smad2/3 activities in Zoep, Moep, and MZoep mutant embryos resulted in more severe mesendodermal defects. Thus, our data reveal that Nodal signaling and mesendoderm induction depend on Smad2/3 and suggest that transforming growth factor-beta signals other than Nodal also contribute to Smad2/3 signaling and embryonic patterning.

Highlights

Through a mechanism that is common to other TGF-␤ members
Another surprising finding is that smad2-deficient cells with the epiblast of chimeric mouse embryos extensively colonize mesodermal and ectodermal populations [10]
Smad2/3 in Mesendoderm Induction indicate that Smad2 and Smad3 play important roles in the mesendoderm by mediating Nodal and non-Nodal signaling during zebrafish embryogenesis

Summary

Introduction

Through a mechanism that is common to other TGF-␤ members. Smad2 and Smad3 are crucial intracellular effectors of Nodal signals [5, 6]. When the same amount of sqt or tar* mRNA was coalso functions as a dominant-negative allele to inhibit TGF-␤ injected with 600 pg of dominant-negative smad2 or smad3b signaling by preventing recruitment of Smad4 from the cyto- mRNA, none of the embryos exhibited induction of plasm into the nucleus to form a transcription activation com- gsc, ntl, or sox32 expression. The similarity between dominant-negative smad2/3-induced and MZoep phenotypes suggests that Smad2/3 activities are required for maternal and zygotic Nodal signaling in mesendoderm induction.

Results

Conclusion