Localization of pro-alpha 2(V) collagen transcripts in the tissues of the developing mouse embryo

Correct assembly of fibrillar collagen networks plays a critical role in animal morphogenesis. Very little is known about the contribution of the so-called minor fibrillar collagens (types V and XI) to fibrillogenesis. Here we examined the developmental expression of the mouse pro-alpha 2(V) collagen gene (col5a2) after the cloning and sequencing of cDNAs that cover the entire length of the message. Transcripts of col5a2, detectable as early as 9 days of gestation, localize with distinct patterns in the tissues of day 12.5 and day 16.5 fetuses. The earlier developmental stage is characterized by low and diffuse col5a2 expression in the peritoneal membranes and intestinal and craniofacial mesenchymes. The later stage exhibits higher and more restricted col5a2 mRNA accumulation in primary ossified regions, perichondrium, joints, tendon, atrioventricular valve of the heart, and selected portions of the head. A parallel analysis using a cartilage-specific pro-alpha 1(II) collagen (col2a1) probe confirmed that these two collagen genes are transcribed in a mutually exclusive manner during mouse embryogenesis. On the other hand, the developmental pattern of col5a2 expression closely resembles that of the type I collagen, thus further substantiating the notion that these macromolecules cooperate in the formation of fibrillar networks in non-cartilaginous matrices.