DISTINCT HEPARIN-BINDING AND NEURITE-PROMOTING PROPERTIES OF LAMININ ISOFORMS ISOLATED FROM CHICK HEART

Laminin isolated from chick heart is composed of several heterotrimeri c variants of 800 and 700 kDa, Here, we used monoclonal antibodies aga inst chick laminin to purify different laminin isoforms from this mixt ure. Antibody 8D3 specifically removed laminin containing alpha 2 chai n from chick heart laminin preparations, leaving behind 700 kDa varian ts, Using antibody C4 against the laminin beta 2 chain, alpha 2 chain containing variants were further separated into alpha 2 beta 1 gamma 1 and alpha 2 beta 2 gamma 1 laminin, respectively. Laminins containing alpha 2 chain and recognized by antibody 8D3 are cross-shaped molecul es. Their expression during embryogenesis is tightly regulated, In 5-d ay embryos staining with monoclonal antibody 8D3 is restricted to the dermamyotome, Older embryos (8 days) express alpha 2 chain containing muscle, and only late in development these variants are generally expr essed in skeletal and heart muscle basement membranes, The 700 kDa lam inin variants contain beta 1, beta 2, and yl subunits affiliated with an immunologically distinct, shorter ax chain and appear to be T-shape d in the electron microscope. Whereas laminins with an alpha 2 subunit bind to heparin, variants with the novel ax chain do not, Experiments using cultured sympathetic neurons showed that laminins with alpha x chain are less potent than alpha 2 chain containing variants in promot ing neurite outgrowth, In contrast, sympathetic neurons cannot discrim inate between alpha 2 beta 1 gamma 1 and alpha 2 beta 2 gamma 1 lamini n substrates, respectively, and show identical high rates of neurite f ormation.