title: Appearance and distribution of laminin A chain isoforms and integrin alpha 2, alpha 3, alpha 6, beta 1, and beta 4 subunits in the developing human small intestinal mucosa.
abstract: BACKGROUND
  Laminin, a major component of basement membranes, is well known in its classical heterotrimeric form (B1-A-B2) to regulate diverse biological functions, including cell polarization and differentiation. However, the role of merosin, a laminin-like molecule in which an M chain is substituted for its homologous A chain, remains largely unknown.
  
  
  METHODS
  In the present study, we analyzed by indirect immunofluorescence the expression and distribution of these four laminin chains as well as the integrins alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, and alpha 6 beta 4, four potential receptors, at the epithelial-mesenchymal interface of the developing human small intestine, with a panel of specific monoclonal antibodies.
  
  
  RESULTS
  Beginning at 7 weeks of gestation and throughout mucosal organogenesis, the B1 and B2 chains were uniformly detected at the epithelial basement membrane. The A chain also was detected beginning at 7 weeks, and its distribution at the basement membrane remained uniform throughout villus (9+ weeks) and crypt (16+ weeks) formation. In contrast, M chain expression was not observed until 16 weeks; between 16 and 20 weeks, it was exclusively associated with the base of epithelial cells that comprised the forming crypts. Integrins alpha 6 beta 1 and alpha 6 beta 4, as determined by their subunit immunolocalization, appeared to be expressed by all enterocytes from 7 to 20 weeks. In contrast, the expression of the alpha 2 beta 1 and alpha 3 beta 1 integrins was found time- and site-restricted. The alpha 2 subunit was predominantly detected in the epithelial cells of the intervillous area and its derivative, the crypt, whereas the alpha 3 subunit was strongly expressed by all epithelial cells except those located at the bottom of 19-20-week-old crypts.
  
  
  CONCLUSIONS
  Taken together, these observations demonstrate that both compositional changes in the basement membrane and differential expression of receptors occur during human intestinal organogenesis, suggesting that epithelial cell-matrix interactions play a role during development.
authors.affiliation: Département d'anatomie et de biologie cellulaire, Faculté de médecine, Université de Sherbrooke, Québec, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Perreault
authors.forename: P H
authors.initials: PH
authors.lastname: Vachon
authors.forename: J F
authors.initials: JF
authors.lastname: Beaulieu
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005865:Gestational Age; D006801:Humans; D039421:Integrin alpha2; D039422:Integrin alpha3; D039503:Integrin alpha6; D019012:Integrin beta1; D039663:Integrin beta4; D016023:Integrins / Q000737:chemistry / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000196:embryology* / Q000378:metabolism*; D007421:Intestine, Small / Q000196:embryology* / Q000378:metabolism*; D007797:Laminin / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D015703:Antigens, CD; D039421:Integrin alpha2; D039422:Integrin alpha3; D039503:Integrin alpha6; D019012:Integrin beta1; D039663:Integrin beta4; D016023:Integrins; D007797:Laminin; C084098:laminin A