Primary structure and expression of a chicken laminin beta chain: evidence for four beta chains in birds.

Characterization of a full length cDNA sequence for a chicken laminin beta chain is described which is most closely related to the mammalian beta 2 chain. Comparison with published sequences shows that the chicken beta 2-like chain corresponds to a fragment of a previously described laminin beta chain called B1-2 (O'Rear, 1992). The sequence of the chicken beta 2-like chain differed from fragments of two other chicken laminin beta chains that were previously described and designated B1-1 (now called beta 1; O'Rear, 1992) and beta x (Ybot-Gonzalez et a1.,1995). In addition, the beta 2- like chain does not appear to be the chicken equivalent of the mammalian laminin beta 3 chain, since it differs markedly in cDNA sequence, possesses domain IV and has a transcript size of 6 kb. We therefore propose that there are at least four laminin beta chains in the chicken. Sequence comparison of the beta 2-like laminin chain with previously cloned beta 1 and beta 2 chains shows a somewhat closer relationship to rat and human beta 2 than to mouse and human beta 1, especially in domains I, II and alpha. In addition, two expressed fragments of the chicken beta 2-like chain were recognized by a monoclonal antibody (C4) regarded as specific for the rat beta 2 chain (Hunter et al., 1989a). The results therefore suggest that the laminin chain previously described as a potentially novel chain called B1-2 (O'Rear, 1992) is likely to be the chicken equivalent of the mammalian beta 2 chain.