Cloacal apoptosis in normal rat embryological development

Objective To investigate the role apoptosis in hindgut morphogenesis in normal El3 to E16 rat embryos. Methods TUNEL staining was performed to detect the apoptotic cells in the cloa- ca of wild-type E13 to E16 rat embryos. Results On E 13,the genital tubercle has fully developed and the cloaca is well formed. The urogenital septum (URS) divided cloaca into urogenital sinus and rec- tum. The tail groove were formed. There were apoptotic cells in the epithelial layers and mesenchyme region of URS. Following the development, genital tubercle grew gradually and shifted ventrocaudally. The tail groove deepened gradually and cloacal membrane rotated dorsalcaudally. The apoptotic cells increased and they descended in the mesenchyme region of URS. Many apoptotic cells appeared in the dorsal mesenchyme of the rectum. On E14,apoptotic cells began to appear at the terminal rectum and the future anal orifice part of cloacal membrane. On E15, URS fused with cloacal membrane and apop- tosis in URS descended to the fusion position. Anal membrane ruptured and rectum communicated with the exterior on E16. Conclusions In cloacal embryological developments, apoptosis is involved in the descend and fusion of URS, the configuration transformation of cloaca, and the rupture of cloacal mem- brane. Key words: Embryo; Cloaca; Apoptosis