TISSUE-SPECIFIC EXPRESSION OF THE FIBRIL-ASSOCIATED COLLAGEN-XII AND COLLAGEN-XIV

Interstitial collagen fibrils form the supporting scaffold of all conn ective tissues. The synthesis of this framework is subject to a precis e spatial and temporal regulation in order to meet the mechanical need s of every tissue type. A subgroup of non-fibrillar collagens termed F ACIT seems to play a role in this regulation by providing specific mol ecular bridges between fibrils and other matrix components. Collagens XII and XIV represent such FACIT molecules and occur preferentially in tissues containing banded type I collagen fibrils. We have used the t echniques of indirect immunofluorescence and in situ hybridization to investigate the expression patterns of the two molecules during chicke n embryonic development. We detected specific differences in these pat terns, which may be related to the respective functions of the two pro teins within the connective tissues. Collagen XIV was expressed at ver y few sites in the 6-day-old embryo, but occurred in virtually every c ollagen I-containing tissue (skeletal muscle, cardiac muscle, gizzard, tendon, periosteum, nerve) by the end of embryonic development. In co ntrast, collagen XII was fairly abundant in the day-old embryo but was , at later stages, restricted to only a few dense connective tissue st ructures (bone, tendon, gizzard), Thus, our results suggest that colla gen XII and collagen XIV serve different functions during embryonic de velopment although their structures are highly similar.