Function Of MDpr2, Zhmg2l1, Zppm1a In The Development Of Embryos

TGFβ/Nodal signaling pathway is one of the most important signaling pathways in the development of embryos. Compared with other signals, TGFβ/Nodal plays a key role in the induction of mesendoderm. Here, my work focused on three genes, mouse Dapper2, zebrafish hmg2l1 and ppm1a, which were all related with TGFβsignaling pathway. Their expression patterns and functions were studied to further illustrate the mechanism of embryonic development.As we have reported, zebrafish Dapper2 acted as an inhibitor of mesoderm development by promoting the degradation of Nodal receptor, however, mammalian Dapper2 has never been reported. Because of the significance of zebrafish Dapper2 in mesoderm induction, the mouse dapper2 was cloned following its homolog. The study of its spatial and temporal expression pattern showed that it expressed specifically in otic vesicle, somite,gut and roof plate of mouse embryos. In the ARE-luciferase reporter assay, mouse Dapper2 can inhibit the activity of TGFβpathway. The overexpression of mouse Dapper2 in zebrafish embryos induced the reduction of mesoderm. All of the results suggested that the effects of Dapper2 in regulating TGFβsignal and zebrafish embryonic development were conserved between zebrafish and mouse.Zebrafish Hmg2l1, which was obtained by yeast two-hybridization using zebrafish Dapper2 as bait, can interact with zebrafish Dapper2. It repressed Wnt signal dependent onβ-catenin and activated TGFβ/Nodal signaling pathway transduced by Smad2/3. The overexpression of hmg2l1 led to the absence of head structure in oep mutant. More work is still needed to explain the mechanism.Zebrafish Ppm1a, a Mg2+-dependent serine/threonine phosphatase, was identified as a Smad2/3-specific phosphatase. It down-regulated TGFβ/Nodal signal by dephosphorylating the activated Smad2/3. Demonstrated by in situ hybridization, zebrafish ppm1a was a maternal gene and expressed throughout the embryos. In the zebrafish, overexpression of ppm1a can inhibit the development of dorsal mesoderm,and the abnormal phenotype can be rescued by injection of the MH2 domain of Smad2 protein. Furthermore, overexpression of ppm1a can rescued the dorsalized phenotype caused by the injection of Smad2-MH2 protein or smad3b mRNA. These results revealed that Ppm1a can down-regulate TGFβ/Nodal signal and affect the development of dorsal mesoderm by interacting with Smad2/3.My work showed that Dapper2, Hmg2l1 and Ppm1a were negative regulators of TGFβ/Nodal signal and they perhaps regulated the development of dorsal structure in vertebrate embryos. These data give some new insights on the mechanism of TGFβ/Nodal transduction and in regulation of embryonic development.