Laminin α5-chain is expressed early and widely during the development of the anterior segment of rat eye

The distribution of a novel laminin α5-chain in the basement membranes of the anterior segment of rat eye was studied. Frozen sections of embryonic day (E)16-17, post-natal day (P)2, 5, 10, 15 and 30 and adult rat eyes were immunostained for laminin chains α2, α5, β1, β2 and γ1 and for laminin- 5, as well as for EHS-laminin, to visualize all basement membranes. Laminin α5-, β1- and γ1-chain immunoreactivities were found in the basement membranes of the inner and outer layers of optic cup, lens epithelium, further corneal epithelium and skin of the eyelids in E16-17 rat eyes. In P2 and older rat eyes, laminin α5-, β1- and γ1-chains were all seen in the basement membranes of the corneal and conjunctival epithelium, Descemet's membrane, lens epithelium, ciliary processes, blood vessels and skin of the eyelids. There was a change in the expression pattern of laminin α5, β1- and γ1-chains in Descemet's membrane from the endothelial side of the membrane (P2-P15 eyes) to both sides of the membrane after P30. Immunoreactivity for laminin-5 was weak in the basement membrane of E16-17 epidermis, but strong in the basement membrane of corneal, conjunctival and eyelid epithelium in P2 and older rat eyes. Laminin α2- and β2-chains were seen in conjunctival and uveal blood vessels in P15 and older rat eyes. The laminin β2-chain emerged into the basement membrane of conjunctival epithelium in P30 and older rat eyes, suggesting a role for the laminin β2- chain in the maturation of conjunctiva. The results suggest that laminin α5- chain, possibly in laminin-10 (α5β1γ1), is early and widely expressed in the basement membranes of developing and adult rat eye and, further, that laminin α5-chain is a major laminin α-chain, partly in coexpression with the α3-chain of laminin-5 in the basement membranes of the anterior segment of the eye in developing and adult rats.