title: Epithelial and muscular regionalization of the human developing anorectum.
abstract: In the past, interpretations of anorectal development were mainly based on analysis of serially sectioned embryos of various nonhuman species as well as some human specimens. A four-dimensional view of the developmental situation in the human has never been established nor connected to recent findings obtained from newer molecular techniques. We, therefore, investigated human embryonic and fetal pelves by means of immunohistochemistry and in situ hybridization to elucidate differentiation and interaction of epithelial and mesenchymal layers of the anorectum. To emphasize spatial as well as sequential morphological development, we produced three-dimensional reconstructions of the specimens at hand. Research conducted proved that the decisive steps of epithelial and muscular differentiation occur between the 7th and 9th week after conception. This study elucidates a biphasic epithelial "closure" in the anal canal and interactions between epithelium, smooth musculature, and skeletal musculature. Based on the results presented here, it is possible to describe the pathogenesis of two anorectal malformations: the imperforate anal membrane and the anal membrane stenosis. This study will now provide the basis for further research into developmental processes occurring before the ones examined.
authors.affiliation: Department of Anatomy, Histology, and Embryology, Division of Clinical and Functional Anatomy, Medical University of Innsbruck, Innsbruck, Austria. helga.fritsch@i-med.ac.at
authors.forename: Helga
authors.initials: H
authors.lastname: Fritsch
authors.forename: Felix
authors.initials: F
authors.lastname: Aigner
authors.forename: Barbara
authors.initials: B
authors.lastname: Ludwikowski
authors.forename: Sandra
authors.initials: S
authors.lastname: Reinstadler-Zankl
authors.forename: Romana
authors.initials: R
authors.lastname: Illig
authors.forename: Dieter
authors.initials: D
authors.lastname: Urbas
authors.forename: Christoph
authors.initials: C
authors.lastname: Schwarzer
authors.forename: Stefano
authors.initials: S
authors.lastname: Longato
mesh_terms: D000199:Actins / Q000378:metabolism; D001003:Anal Canal / Q000002:abnormalities / Q000196:embryology / Q000378:metabolism; D004848:Epithelium / Q000196:embryology / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D053538:Keratin-18 / Q000378:metabolism; D009024:Morphogenesis; D018482:Muscle, Skeletal / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D012007:Rectum / Q000002:abnormalities / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D000199:Actins; C513184:HOXD13 protein, human; D018398:Homeodomain Proteins; D053538:Keratin-18; D014157:Transcription Factors; D009218:Myosins