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

Components of the extracellular matrix exert myriad effects on tissues thro ughout the body. In particular, the laminins, a family of heterotrimeric ex tracellular glycoproteins, have been shown to affect tissue development and integrity in such diverse organs as the kidney, lung, skin, and nervous sy stem. Of these, we have focused on the roles that laminins play in the diff erentiation and maintenance of the nervous system. Here, we examine the exp ression of all known laminin chains within one component of the CNS, the re tina. 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. Anatomicall y, these chains are coexpressed in one or both of two locations: the matrix surrounding photoreceptors and the first synaptic layer where photorecepto rs synapse with retinal interneurons. Biochemically, four of these chains a re coisolated from retinal extracts in two independent complexes, confirmin g that two novel heterotrimers-alpha 4 beta 2 gamma 3 and alpha 5 beta 2 ga mma 3-are present in the retinal matrix. During development, all four of th ese chains, along with components of laminin 5 (the alpha 3, beta 3, and ga mma 2 chains) are also expressed at sites at which they could exert importa nt effects on photoreceptor development. Together, these data suggest the e xistence 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 lamini n 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 ph otoreceptor production, stability, and synaptic organization.