Laminin expression in adult and developing retinae: Evidence of two novel CNS laminins

Components of the extracellular matrix exert myriad effects on tissues throughout the body. In particular, the laminins, a family of heterotrimeric extracellular glycoproteins, have been shown to affect tissue development and integrity in such diverse organs as the kidney, lung, skin, and nervous system. Of these, we have focused on the roles that laminins play in the differentiation and maintenance of the nervous system. Here, we examine the expression of all known laminin chains within one component of the CNS, the retina. We find seven laminin chains-alpha 3, alpha 4, alpha 5, beta 2, beta 3, gamma 2, and gamma 3-outside the retinal basement membranes. Anatomically, these chains are coexpressed in one or both of two locations: the matrix surrounding photoreceptors and the first synaptic layer where photoreceptors synapse with retinal interneurons. Biochemically, four of these chains are coisolated from retinal extracts in two independent complexes, confirming that two novel heterotrimers-alpha 4 beta 2 gamma 3 and alpha 5 beta 2 gamma 3-are present in the retinal matrix. During development, all four of these chains, along with components of laminin 5 (the alpha 3, beta 3, and gamma 2 chains) are also expressed at sites at which they could exert important effects on photoreceptor development. Together, these data suggest the existence of two novel laminin heterotrimers in the CNS, which we term here laminin 14 (composed of the alpha 4, beta 2, and gamma 3 chains) and laminin 15 (composed of the alpha 5, beta 2, and gamma 3 chains), and lead us to hypothesize that these laminins, along with laminin 5, may play roles in photoreceptor production, stability, and synaptic organization.