Normal development of hindgut and anorectum in human embryo.
OBJECTIVE
The aim of the present analysis is to examine the morphological changes, the spatiotemporal distribution of apoptosis/proliferation in the human embryonic anorectum, to reveal the normal development of human anorectum, and investigate the possible roles of apoptosis/proliferation during anorectal development.


METHODS
The embryos were sectioned serially and sagittally, stained with hematoxylin and eosin (H & E) between the third and eighth week of gestation, TdT-mediated dUTP-digoxigenin nick end-labeling (TUNEL) and proliferative cell-specific nuclear antigen (PCNA) immunohistochemical staining from the sixth to the eighth week.


RESULTS
From the fourth to the seventh week, with the growth of the mesenchyme around the cloaca, the cloaca was remolded, subsequently, the cloacal membrane (CM) moved perpendicularly then horizontally. The dorsal cloaca gradually descended to the tail groove, the urorectal septum (URS) and the CM approximated; however, the fusion of URS with the dorsal CM was never observed. During the eighth week, the URS shifted ventrally and finally fused with the ventral CM. Moreover, from the sixth to the eighth week, the apoptotic cells were concentrated in the CM, the mesenchyme of terminal rectum, and the dorsal rectum. Meanwhile, the proliferative cells could be observed in the ventral mesenchyme around the cloaca, the CM, the fused tissue between the URS, and the ventral CM.


CONCLUSIONS
During the development of human anorectum, it was intriguing to reveal that the URS never fused with the dorsal CM before dorsal CM disintegration, the normal anorectal development may depend on the dorsal cloaca and the dorsal CM; furthermore, the distribution of apoptosis and proliferation in the anorectum and ventral cloacal mesenchyme played a pivotal role in the formation of the anorectum.
Zhang
Tao
T
Department of Pediatric Surgery, Shengjing Hospital, China Medical University, No. 36 Sanhao Street, Heping District, Shenyang 110004, People's Republic of China.
Zhang
Hai Lan
HL
Wang
Da Jia
da J
Tang
Xiao Bing
XB
Jia
Hui Min
HM
Bai
Yu Zuo
YZ
Yuan
Zheng Wei
ZW
Wang
Wei Lin
WL
D001003:Anal Canal / Q000166:cytology / Q000196:embryology*; D017209:Apoptosis; D049109:Cell Proliferation; D004622:Embryo, Mammalian / Q000033:anatomy & histology* / Q000166:cytology / Q000196:embryology*; D006801:Humans; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012007:Rectum / Q000166:cytology / Q000196:embryology*; D013997:Time Factors
D018809:Proliferating Cell Nuclear Antigen