SPATIAL AND TEMPORAL CHANGES OF TYPE-VI COLLAGEN EXPRESSION DURING MOUSE DEVELOPMENT

The expression of type VI collagen has been studied in mouse tissues. By Northern blotting, the mRNA for the alpha 1(VI) chain was detectabl e in whole embryos at 10.5 days postcoitum and steeply increased after ward. The messenger levels were high at birth, but decreased rapidly i n the following days, reaching low levels in adult animals. In 2-month -old mice, lung, skin, adrenal gland, heart, skeletal muscle and tail and fat were among the most active producers of alpha 1(VI) mRNA. In s itu hybridization first identified mRNA for alpha 1(VI) collagen in me senchymal cells of 10.5-day embryos in various locations, including se rosae, branchial arches, large blood vessels and the cephalic mesenchy me. Staining increased at later stages of development and mesa; connec tive tissues were positive at 16.5 days and later. Strongly staining t issues were joints, intervertebral disks, perichondrium, periostium, d ermis, skeletal muscle and heart valves, whereas cartilage and bone we re very poorly labelled. Epithelia and the central nervous system were completely negative. In several organs, notably lung, salivary glands and the digestive tract, staining was concentrated underneath epithel ia. This staining pattern was different from that for collagen type I, which was evenly distributed in the subepithelial mesenchyme. The pat tern of distribution of the protein, revealed by immunocytochemistry, was coincident with that of the alpha 1(VI) mRNA. In addition, the res ults confirmed that type VI collagen is preferentially deposited in th e pericellular environment. This was particularly evident in skeletal muscle. The data show that type VI collagen is mainly produced by mese nchymal cells and suggest a role for the protein in delineating the bo undary of distinct domains in connective tissue. (C) 1996 Wiley-Liss, Inc.