CHANGES IN THE DISTRIBUTION OF INTEGRINS AND THEIR BASEMENT-MEMBRANE LIGANDS DURING DEVELOPMENT OF HUMAN THYROID FOLLICULAR EPITHELIUM

Interactions between cells and basement membrane components are crucia l for the regulation of epithelial cell differentiation and polarizati on. We have studied by immunohistochemical methods the distribution of integrin adhesion proteins and some of their basement membrane ligand s in foetal (16-19 weeks) and adult thyroid follicular epithelia. A di ffuse immunoreactivity for only alpha(3), alpha(v) and beta 1 integrin s was found in foetal follicular epithelium, whereas in adult follicul ar epithelium these integrins were expressed basally in a polarized ma nner. Additionally, beta(3) integrin was seen in a more basolaterally confined manner in adult follicular epithelium. Among basement membran e components, laminin alpha 1, beta 1, gamma 1 and beta 2 chains were found in epithelial basement membranes of the foetal thyroid gland, su ggestive of the presence of laminins-1 and -3. In contrast, the baseme nt membranes of adult follicular epithelium presented a much weaker im munoreactivity for the laminin beta 2 chain. Furthermore, immunoreacti vity for the laminin alpha 2 chain was occasionally seen in adult thyr oid glands, apparently confined to myofibroblasts. Immunoreactivity fo r type IV collagen alpha 1 and alpha 2 (IV) chains was found in follic ular basement membranes of foetal as well as adult thyroid gland. The results suggest that during maturation of foetal thyroid follicular ep ithelium a distinct polarization of integrins takes place. In mature t hyroid follicular epithelium, the presumable adhesion-mediating integr in complexes are alpha(3) beta(1), alpha(v) beta(1) and/or alpha(v) be ta(3) mediating adhesion to laminin-1 (alpha 1-beta 1-gamma 1) and typ e IV collagen trimer alpha 1(2) alpha 2 (IV).