Differential and restricted expression of novel collagen VI chains in mouse.

Recently, three novel collagen VI chains, ±4, ±5 and ±6, were identified. These are thought to substitute for the collagen VI ±3 chain, probably forming ±1±2±4, ±1±2±5 or ±1±2±6 heterotrimers. The expression pattern of the novel chains is so far largely unknown. In the present study, we compared the tissue distribution of the novel collagen VI chains in mouse with that of the ±3 chain by immunohistochemistry, immunoelectron microscopy and immunoblots. In contrast to the widely expressed ±3 chain, the novel chains show a highly differential, restricted and often complementary expression. The ±4 chain is strongly expressed in the intestinal smooth muscle, surrounding the follicles in ovary, and in testis. The ±5 chain is present in perimysium and at the neuromuscular junctions in skeletal muscle, in skin, in the kidney glomerulus, in the interfollicular stroma in ovary and in the tunica albuginea of testis. The ±6 chain is most abundant in the endomysium and perimysium of skeletal muscle and in myocard. Immunoelectron microscopy of skeletal muscle localized the ±6 chain to the reticular lamina of muscle fibers. The highly differential and restricted expression points to the possibility of tissue-specific roles of the novel chains in collagen VI assembly and function.