Characterization and expression of the laminin gamma 3 chain: A novel, non-basement membrane-associated, laminin chain

Laminins are heterotrimeric molecules composed of an alpha, a beta, and a g amma chain; they have broad functional roles in development and in stabiliz ing epithelial structures. Here, we identified a novel laminin, composed of known alpha and beta chains but containing a novel gamma chain, gamma 3. W e have cloned gene encoding this chain, LAMC3, which maps to chromosome 9 a t q31-34. Protein and cDNA analyses demonstrate that gamma 3 contains all t he expected domains of a gamma chain, including two consensus glycosylation sites and a putative nidogen-binding site. This suggests that gamma 3-cont aining laminins are likely to exist in a stable matrix. Studies of the tissue distribution of gamma 3 chain show that it is broadly expressed in: skin, heart, lung, and the reproductive tracts. In skin, gam ma 3 protein is seen within the basement membrane of the dermal-epidermal j unction at points of nerve penetration. The gamma 3 chain is also a promine nt element of the apical surface of ciliated epithelial cells of: lung, ovi duct, epididymis, ductus deferens, and seminiferous tubules. The distributi on of gamma 3-containing laminins on the apical surfaces of a variety of ep ithelial tissues is novel and suggests that they are not found within ultra structurally defined basement membranes. It seems likely that these apical laminins are important in the morphogenesis and structural stability of the ciliated processes of these cells.