Type VIII collagen in murine development. Association with capillary formation in vitro.

Bovine endothelial and human astrocytoma cells, and a limited number of other normal and malignant cells, synthesize three chains that have been identified as type VIII collagen (180 kDa, 125 kDa, and 100 kDa). Digestion with pepsin converts these forms to major fragments of 65 kD (based on globular protein standards). In this study we have examined the structure and distribution of type VIII collagen in developing mice by immunohistological and immunoblotting techniques. Temporal and tissue-specific expression was observed in embryonic heart, cranial mesenchyme, and placental capillaries. Western blotting of embryonic and neonatal tissues showed major species of 125 and 65 kDa in the brain, placenta, heart, lung, and thymus. The predominant band in pepsin-treated tissues was 60-70 kDa, with additional forms of 250 and 150 kDa in neonatal heart and lung. Type VIII collagen was also synthesized by endothelial cells, forming capillary tubes in vitro. We suggest that type VIII collagen functions in cellular organization and differentiation, and that its various forms reflect not only tissue-specific processing but the presence of several related chains.