title: Apoptosis during regression of the tailgut and septation of the cloaca.
abstract: OBJECTIVE
  Apoptosis is involved in the embryonic morphogenesis of many organs. The current study was undertaken to ascertain the role of apoptosis during cloacal development in the rat.
  
  
  METHODS
  One hundred five rat embryos, ranging from gestational days 11 to 16, were sectioned serially in the transverse or sagittal planes and stained with H&E. The cloaca, urorectal septum, rectum, urogenital sinus, Wolffian ducts, and tailgut (TG) were examined consecutively in temporospatial sequence.
  
  
  RESULTS
  The tailgut immediately distal to the hindgut starts to regress by apoptosis on day 12 of gestation in a craniocaudal direction and has regressed completely by day 13.5. A large number of apoptotic cells and debris can be identified in the urorectal septum during cloacal septation. Vacuoles are formed by coalescence of apoptotic cells at the tip of urogenital sinus from day 15 to 16, and, at the same time, sporadic apoptotic bodies in the anal membrane contribute to its thinning.
  
  
  CONCLUSIONS
  Results of the current study confirm that apoptosis occurs in a specific temporo-spatial sequence in the hindgut and cloaca and appears to be an important mechanism in TG regression, uro-rectal separation, urethral opening, and rupture of the anal membrane.
authors.affiliation: Department of Paediatric Surgery, Christchurch Hospital, New Zealand.
authors.forename: B Q
authors.initials: BQ
authors.lastname: Qi
authors.forename: S W
authors.initials: SW
authors.lastname: Beasley
authors.forename: A K
authors.initials: AK
authors.lastname: Williams
authors.forename: F
authors.initials: F
authors.lastname: Fizelle
mesh_terms: D000818:Animals; D017209:Apoptosis; D002988:Cloaca / Q000196:embryology* / Q000473:pathology*; D005260:Female; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012002:Rectal Diseases / Q000473:pathology; D012007:Rectum / Q000196:embryology* / Q000473:pathology*; D012680:Sensitivity and Specificity