title: smad2 and smad3 are required for mesendoderm induction by transforming growth factor-beta/nodal signals in zebrafish.
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.
authors.affiliation: Protein Science Laboratory of the Ministry of Education, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China.
authors.forename: Shunji
authors.initials: S
authors.lastname: Jia
authors.forename: Zhen
authors.initials: Z
authors.lastname: Ren
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Zheng
authors.forename: Anming
authors.initials: A
authors.lastname: Meng
mesh_terms: D028341:Activins / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D030801:Animals, Genetically Modified / Q000196:embryology / Q000235:genetics; D019521:Body Patterning / Q000502:physiology; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D005799:Genes, Dominant / Q000235:genetics; D008648:Mesoderm / Q000196:embryology*; D055457:Nodal Protein; D015398:Signal Transduction / Q000502:physiology; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C079678:Gdf3 protein, zebrafish; D055457:Nodal Protein; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D029961:Zebrafish Proteins; C497786:smad2 protein, zebrafish; C497792:smad3a protein, zebrafish; D028341:Activins