A variety of extracellular matrix (ECM)
proteins have been shown to be present in the embryonic heart during the morphogenesis of the valves and membranous septa. It is not known if any specific ECM
protein is required for the normal morphogenesis of these tissues, but this is of great interest since there is a high incidence of congenital malformations which affect valvular and septal tissues. Interestingly, the alpha 1 and alpha 2 genes of
type VI collagen are located within the region of human chromosome 21 thought to be involved in the
congenital heart defect phenotype associated with
trisomy 21 (
Down's syndrome). In this study we examined the distribution and investigated the function of
type VI collagen in the cardiac valves and septa of chicken and mouse embryos during various stages of development. Immunohistochemical and in situ hybridization studies revealed a pattern of cardiac expression of
type VI collagen which is present from the earliest stages of valve and septum development through the neonatal period. Results from an in vitro bioassay suggest that
type VI collagen may play a role in the formation and migration of specific cells in the forming valves and septa. These data support molecular genetic studies which have indicated that
type VI collagen is involved in the heart defect phenotype seen in
trisomy 21.