Fig. 4. Differential gene expression during capillary morphogenesis as determined by western blot analysis and immunohistochemistry. EC-collagen gel extracts or conditioned medium were prepared or collected at the indicated time points. Samples were run on SDS-PAGE and, after blotting, were probed with antibodies directed to various proteins. Cell extracts were probed with antibodies directed to collagen type IV, ₂-macroglobulin and Id-1. Conditioned medium samples were probed with antibodies directed to collagen type IV or laminin. The arrows in the collagen type IV blots represent the 1 and 2 chains of collagen type IV. Arrows indicate the position of molecular weight markers on the blots. In B, a 48 hour culture was stained with antibodies to collagen type IV under non-permeabilizing conditions. No staining was observed without the addition of the primary anti-collagen type IV antibody. Bar, 50 µm.