Functional Study Of Bmp Signaling Pathway In The Development Of Zebrafish Cloaca

The development of cloaca is a complex and delicate process that requires the co-regulation of different signaling pathways and essential molecules. In recent years, increasing attention is drawn to hereditary disease related to anus defects. Zebrafish cloaca is the counterpart of anus in mammals. Study on cloaca development will greatly improve our understanding of these diseases, which is helpful to understand the anus defects in human. Although the morphological process of cloaca development in mouse is well studied, the molecular mechanism still remains unclear. Taking advantage of the zebrafish in embryology and genetics, we first observed the development of the cloaca in zebrafish embryos and found that the development of cloaca in zebrafish is similar to the mammals. Then, we tried to intervene the BMP signaling by heat-shock in the transgenic zebrafish lines Tg(hsp70:bmp2b) and Tg(hsp70:bmpDNR-GFP) to up-regulate and down-regulate BMP signaling pathway respectively, and found that the phenotype of the two transgenic embryos are very similar to human congenital anorectal. This would help to study the mechanism of related diseases.To study the cloaca development in zebrafish. A number of genes which were expressed in cloaca had been cloned. And we used RNA in situ hybridization to study the expression of these genes, and found two genes, hoxdl3a and aqp3a, were expressed at different stages during the development of cloaca. And then, we observed the effects of BMP signaling up regulation and down regulation on the development of cloaca inTg(hsp70:bmp2b) and Tg(hsp70:bmpDNR-GFP) transgenic lines respectively.Results showed that the cloaca development would be affected when BMP signaling was intervened during the gastrulation, this further proved that the BMP signaling was necessary for the cloacal development. Down-regulation of the BMP signaling could cause the proctodeum defects of cloaca, while the up-regulation of the BMP signaling would lead to overgrowth of the renal terminal and the proctodeum. We found that the change of the BMP signaling not only resulted in the loss function of evacuation but also affected the cell apoptosis in the cloaca, but the molecular mechanism still remains unclear.