Characterization and Expression of the Laminin g 3 Chain: A Novel, Non-Basement Membrane–associated, Laminin Chain

Laminins are heterotrimeric molecules composed of an a , a b , and a g chain; they have broad functional roles in development and in stabilizing epithelial structures. Here, we identified a novel laminin, composed of known a and b chains but containing a novel g chain, g 3. We have cloned gene encoding this chain, LAMC3, which maps to chromosome 9 at q31-34. Protein and cDNA analyses demonstrate that g 3 contains all the expected domains of a g chain, including two consensus glycosylation sites and a putative nidogenbinding site. This suggests that g 3-containing laminins are likely to exist in a stable matrix. Studies of the tissue distribution of g 3 chain show that it is broadly expressed in: skin, heart, lung, and the reproductive tracts. In skin, g 3 protein is seen within the basement membrane of the dermal-epidermal junction at points of nerve penetration. The g 3 chain is also a prominent element of the apical surface of ciliated epithelial cells of: lung, oviduct, epididymis, ductus deferens, and seminiferous tubules. The distribution of g 3-containing laminins on the apical surfaces of a variety of epithelial tissues is novel and suggests that they are not found within ultrastructurally 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.