FIBULIN-1, VITRONECTIN, AND FIBRONECTIN EXPRESSION DURING AVIAN CARDIAC-VALVE AND SEPTA DEVELOPMENT

Background: Extracellular matrix (ECM) proteins have been implicated a s mediators of events important to valvuloseptal development (reviewed by Little and Rongish, Experentia, 51:873-882, 1995). The aim of this study was to identify connective tissue ECM proteins present at sites of valvuloseptal morphogenesis, and to determine how their patterns o f expression change during the developmental process. Methods: Immunof luorescence microscopy was used to examine the distribution of fibulin -1, vitronectin, and fibronectin in the embryonic chicken heart over a 'broad developmental time frame (Hamburger and Hamilton stages 14 to 44), emphasizing stages that illustrate endocardial cushion formation, growth, fusion, and development into valvuloseptal components. Result s and Conclusions: Fibulin-1 immunolabeling was concentrated in endoca rdial cushions, notably at boundaries with the myocardium, during stag es when the cushions are differentiating into valvular and septal comp onents, Fibulin-1 was detected in the endocardial cushions prior to th eir seeding with cushion cells, but became undetectable by early midge station, Vitronectin expression was similar to fibulin-1, but less res tricted in its distribution, Vitronectin was observed before endocardi al cushion cell migration commenced and persisted until the formation of prevalvular structures (early midgestation) in the atrioventricular cushions. Vitronectin remained detectable in the semilunar valves unt il late midgestation. Fibronectin was present in the endocardial cushi on region and in portions of the endocardium and myocardium throughout the stages presented, Our data suggests that the ECM of the endocardi al cushions undergoes remodelling in a regionally and temporally speci fic manner which corresponds with morphogenetic changes during valvulo septal development. (C) 1996 Wiley-Liss, Inc.