Localized distribution of alpha 9 integrin in the cornea and changes in expression during corneal epithelial cell differentiation.

A recently characterized integrin alpha-chain, alpha 9, forms heterodimers with the integrin beta 1-chain and is present in the skin with a distribution similar to that of alpha 2 and alpha 3, other beta 1 integrins. To determine whether alpha 9 is expressed in the stratified squamous epithelium of the cornea, we used immunohistochemical techniques to compare the distribution of alpha 9 in the adult mouse cornea with that of alpha 3. Abundant alpha 9 was expressed in the lateral and basal membranes of the basal cells of the conjunctiva and corneal limbus, but very little alpha 9 was present in the basal cells of the central corneal epithelium. In contrast, alpha 3 was present in the membranes of basal cells of the conjunctiva, limbus, and central cornea. To determine when during postnatal maturation of the corneal epithelium alpha 9 becomes restricted to the limbus, we looked at the distribution of alpha 9 and alpha 3 in the developing mouse eye from birth to eyelid opening. At birth, the basal cells of the cornea and developing limbal region did not express alpha 9, but there was abundant alpha 9 expressed in suprabasal cells between the fused lids and in the basal cells of the skin and conjunctiva. In contrast, alpha 3, integrin was expressed uniformly in the basal cells across the surface of the conjunctiva, limbus, and cornea and was present only in the basal cells of the epithelium between the fused eyelids. In the central cornea, alpha 9 expression increased in basal cells up until Day 10 after birth. After Day 10, alpha 9 expression in the central cornea began to decrease; after the lids were open, alpha 9 expression in the central cornea became restricted to the limbus. In the basal and suprabasal cells between the fused eyelids expression of alpha 9 became increasingly restricted over time to the basal cells. Recent data suggest that alpha 9 beta 1 can interact with tenascin. Our dual labeling confocal microscopy studies indicate that localization of alpha 9 and tenascin are not coordinated in the developing mouse cornea. Many recent studies have shown an important role for beta 1 integrins in mediating epithelial cell differentiation in vitro; in vivo, changes in integrin expression have been found in wound healing, psoriasis, and in basal and squamous cell carcinomas.(ABSTRACT TRUNCATED AT 400 WORDS)