DEVELOPMENTAL EXPRESSION OF LAMININ BETA-2 IN RAT RETINA - FURTHER SUPPORT FOR A ROLE IN ROD MORPHOGENESIS

Purpose. The authors previously hypothesized that laminin beta 2 (S-la minin) plays a role in directing photoreceptor development. The aim of this study was to examine the temporal and spatial expression pattern of beta 2 laminins in rat retina to test this hypothesis. Methods, Re tinas from Sprague-Dawley rats were harvested on embryonic days (E) 14 , 16, and 21, as well as on postnatal days (P) 2, 5, and 10. Cryostat sections were probed with antibodies directed against beta 2 laminin, laminin-l (alpha 1-beta 1-gamma 1), and von Willebrand factor. Results . At the onset of rod photoreceptor birth (E14), laminin beta 2 surrou nds the cells of the retinal pigmented epithelium (RPE) and is present on the apical surface of the retinal neuroepithelium. At E16, laminin beta 2 persists on the apical surface of the neuroepithelium and the subjacent apical surface of the RPE. At birth, laminin beta 2 fills th e matrix between the juxtaposed surfaces of the RPE and neuroepitheliu m; moreover, laminin beta 2 immunoreactivity penetrates the neural ret ina. Throughout postnatal development, laminin beta 2 immunoreactivity surrounds maturing inner and outer segments. Laminin beta 2 also is f ound in association with blood vessels in the neural retina itself, as well as with choroidal blood vessels; in both places, it is co-locali zed with an endothelial marker, von Willebrand factor, and laminin-l. Conclusions. The spatial and temporal expression of laminin beta 2 is consistent with its hypothesized role in rod development. Laminin beta 2 is in a unique position to interact with mitotically active cells ( in early retinal development), uncommitted progenitors (in late embryo nic development), developing rods (in early postnatal development), an d mature outer segments (throughout adulthood). Together with our earl ier functional data, these data support our hypothesis that this molec ule is an important component of the interphotoreceptor matrix.