Investigations On Several Development-related Signaling Pathway Components

Vertebrate embryonic patterning requires several conserved inductive signals, including Nodal,Bmp,Wnt,Hedgehog and Fgf signals,which have shown to constitute a complex regulatory network that are responsible for all the events in embryogenesis.Left-right(L-R) axis is one of the three major axes in vertebrates.The generation of L-R asymmetry also requires interaction of many signals.The first part of this study firstly discovers a second role of Wnt signaling in L-R regulation of somitogenesis,using LiCl chloride(LiCl) as a specific activator of canonical wnt signaling.,Our data show when embryos are treated by LiCl at early-gastrulation,asymmetric somites are found in early somite stage.The bilateral symmetric expressions of herl and fgf8a,two critical members in segmentation model, are desynchronized in LiCl-treated embryos.L-R asymmetries of the heart and liver are also defective in the subsequent development.However,the expressions of Nodal pathway components(southpaw,lefty1 and pitx2a) do not correspondingly changed. These results demonstrate defects in somitogenesis and organ asymmetries induced by LiCl are not due to the interruption of Nodal signaling.Moreover,aberrant spaw expressions after LiCl treatment probably result from the impairment of the notochord development in zebrafish.Hedgehog signaling plays a multiple role in many processes,including cell proliferation,cell-fate determination and differentiation of various tissues.In vertabrates,Sonic hedgehog acts as a morphogen that induces cells into different cell fates by different concentration.The second part of this study firstly focuses on the phylogenesis,genomics and express pattern of several important members of Hedgehog signaling in amphioxus.In this part,we have shown Hedgehog pathway genes(hedgehog,patched,smoothened, gli and suppressor-of-fused) are based on the vertebate branches.In genomic structure of these genes,amphioxus is more similar to vertebrates.Amphioxus tends to possess more exons than Drosophila and zebrafish and human.These results indicate the Hedgehog pathway genes in amphioxus still have primitive characteristics in gene regulatory.In expression pattern,these genes have many similarities to each other including somite,archenteron and head mesoendoderm and to homologes in Drosophila and vertebrates.This demonstrates Hedgehog signaling is evolutionary conserved.The third part of this study is mainly on Ecsit in zebrafish embryogenesis.Ecsit is so far the only known intermediate between Toll and Bmp signaling in vertebrates and plays a critical role in both embryogenesis and immunity regulation.By injection of Ecsit morpholino into 1-cell stage of zebrafish embyos,we find that most BMP signaling,including bmp4,vox and evel are inhibited.These results show Ecsit conveys part of Bmp signaling.Futhermore,early macrophage marker gene lcp1 is also suppressed,which show Ecsit may involve in maturation of macrophages.