Versican expression is associated with chamber specification, septation, and valvulogenesis in the developing mouse heart.

The versican (PG-M) gene encodes a chondroitin sulfate proteoglycan that is nonpermissive for cell migration and appears in association with slow cell proliferation and cytodifferentiation. Using the techniques of in situ hybridization and immunocytochemistry on sectioned mouse embryos, we found that the mRNA and protein for versican show similar distributions and are expressed in a dynamic pattern during development of the heart. Versican exhibits generalized expression in the tubular heart but becomes rapidly downregulated in the atrium and exhibits higher transcript levels on the right side of the ventricular chamber than the left, before the onset of ventricular septation. Versican is expressed strongly in the trabeculated ventricular myocardium, whereas the compact proliferative zone has lower transcript abundance. It is expressed in the outer layers and on the crest of the ventricular septum and is prominent on the mesenchymal cap of the primary atrial septum. Versican is particularly strongly expressed in the endocardial cushions of the atrioventricular and outflow tract regions and in the atrioventricular, semilunar, and venous valves. This study raises the possibility that versican may be involved in specification of the ventricular chambers, in growth and fusion of the atrial and ventricular septa, and in the transformation from epithelium to mesenchyme that characterizes development of the endocardial cushions. Versican may be a key participant in cardiogenesis, responding to the many diffusible signals that mediate interactions between the developing endocardium and myocardium.