Exogenous laminin promotes astrocyte migration and rescues the astrocyte-migration defect in laminin-null explants. (A-D) Migration of astrocytes (GFAP+) from agarose suspension onto coverslips coated with indicated substrates was analyzed after 6 days. Cells in the suspension remained rounded; those penetrating the drop flatten onto the substrate (A-C). Astrocyte migration and spreading on EHS-laminin was significantly enhanced compared with other isoforms (D). Error bars indicate s.d. (*P<0.04). (E-H) The spread of astrocytes (GFAP+) out of P7 ONH explants was enhanced by exogenous laminin in a isoform-specific manner. (H) The area covered by astrocytes that migrated from ONH explants were quantified; a single representative experiment is shown here. (I-M) Exogenous laminin (EHS-laminin) restores astrocyte migration in an organotypic culture of Lamb2:c3-/- retina. In untreated P1 retina, GFAP+ astrocytes remain clustered around the ONH (arrow, I); they also maintain an immature spindle shape (J, magnified from I, as indicated). Addition of EHS-laminin restored astrocyte migration (K, arrow, ONH) and maturation of shape (L, magnified from K as indicated). (M) The area over which astrocytes spread was quantified and recorded. Error bars represent s.d. (**P<0.002). Scale bars: in I, 200 μm for I and K; 40 μm for J and L; in G, 40 μm for E-G.