The laminin proteins form one of the major networks within basement membranes and are required during development. Five laminin α, three laminin β and three laminin γ subunits are known in vertebrates and over 12 heterotrimeric laminin

The laminin proteins form one of the major networks within basement membranes and are required during development. Five laminin α, three laminin β and three laminin γ subunits are known in vertebrates and over 12 heterotrimeric laminin isoforms are thought to be assembled (Burgeson et al., 1994; Iivanainen et al., 1995; Miner et al., 1995). In vertebrates and invertebrates, laminin isoforms are widely distributed and a variety of phenotypes have been associated with the disruption of different laminins. For example, laminin α2 mutations are found in some congenital muscular dystrophies (HelblingLeclerc et al., 1995; Sunada et al., 1994; Xu et al., 1994); laminin α3, β3 or γ2 mutations are found in junctional epidermolysis bullosa, a skin blistering disease (Aberdam et al., 1994; Kuster et al., 1997; McGrath et al., 1995); and mutations of the laminin β2 chain gene disrupts neuromuscular and renal function (Noakes et al., 1995). Multiple defects are observed in mice that lack the laminin α5 chain and the animals arrest late in embryogenesis (Miner et al., 1998). Mutations in zebrafish indicate that laminin β and γ subunits are important for notochord development (Parsons et al., 2002). In Drosophila, the two laminin α subunits are required for embryonic viability; mutants have defects in the morphogenesis of heart, somatic muscle and trachea (Henchcliffe et al., 1993; Martin et al., 1999; Yarnitzky and Volk, 1995). Furthermore, there is evidence that one of the Drosophila laminin α subunits is required for the follicle cell/oocyte signaling that establishes the anteroposterior axis of the organism (Deng and Ruohola-Baker, 2000). Although genetic studies have established the diversity and complexity of laminin functions in vivo, the manner by which laminins mechanistically regulate development is not well understood. Traditionally, laminin and basement membranes have been viewed at substrates that support cell adhesion and migration. However, the idea that the supramolecular organization of laminin itself has an instructive role has gained support (Colognato and Yurchenco, 2000). On the surface of 3343 Development 130, 3343-3358 © 2003 The Company of Biologists Ltd doi:10.1242/dev.00481