Integrin expression during human epidermal development in vivo and in vitro

In order to investigate the role of extracellular matrix receptors of the integrin family in establishing the spatial organization of epidermal kerotinocytes, we used immunofluorescence microscopy to examine the expression of a range of integrin subunits during development of human palm and sole skin. All of the integrins expressed during development were also present in mature epidermis and were largely confined to the basal layer of keratinocytes in a pericellular distribution. The alpha 3 and beta 1 subunits were expressed prior to the initiation of stratification and did not change in abundance or distribution during subsequent development. alpha 4 and beta 3 were not detected at any time in the epidermis. Every other subunit examined showed spatial or temporal changes in expression. Staining for alpha 1 was strong before stratification and until mid-development, but was greatly decreased in neonatal epidermis. alpha 2 was first detected in small patches of basal cells prior to stratification, and thereafter was found in the entire basal layer, with greater staining in developing sweat glands. alpha 5 was not expressed until mid-development, and then primarily in developing sweat glands, with faint expression in neonatal epidermis. alpha v was detected following stratification, in developing sweat glands, and occasionally in neonatal epidermis. alpha 6 and beta 4 were peribasally expressed before stratification, but thereafter became concentrated at the basal cell surface in contact with the basement membrane, co-localizing with hemidesmosomes as determined by staining with bullous pemphigoid antiserum. We also examined the distribution of three known ligands for keratinocyte integrins: laminin and collagen type IV were present in the basement membrane zone at all stages of development, whereas fibronectin was only evident there until about 13 weeks estimated gestational age. Finally, we found that the changes in integrin expression that occur on initiation of stratification in vivo could be reproduced in organ cultures of developing skin; such cultures therefore provided a useful experimental model for further studies of the role of integrins in epidermal stratification.