COORDINATE PATTERNS OF EXPRESSION OF TYPE-I AND TYPE-III COLLAGENS DURING MOUSE DEVELOPMENT

The extracellular proteins types I and III collagen are abundantly exp ressed during development. Here, the patterns of the pro alpha 1(I), p ro alpha 2(I), and pro alpha 1(III) collagen mRNAs are systematically examined from 7.5 to 17.5 days of development (E7.5 to E17.5) in the m ouse using in situ hybridization with specific riboprobes. Coordinated expression of pro alpha 1(I) and pro alpha 2(I) collagen mRNA was fou nd throughout development in all regions examined. Widespread type I c ollagen expression starting at E8.5 occurred in embryonic mesoderm, sc lerotomes, dermatomes, and in the forming connective tissues. After E1 4.5, regions of ossification showed highest levels of type I collagen expression. Pro alpha 1(III) collagen expression was specific to and c oordinated with patterns of type I collagen expression in many fibrobl ast-containing tissues. No expression of type III collagen occurred in osteoblasts. This comprehensive study of the transcripts of abundantl y expressed structural proteins should provide a basis for comparison of other key extracellular matrix molecules and serve as a reference f or studies on the patterns of activities of various promoter/enhancer- reporter gene constructions of type I and III collagen genes in transg enic mice.