DEVELOPMENT OF THE EPICARDIUM IN THE DOGFISH (SCYLIORHINUS-CANICULA)

The development of the epicardium has been described in mammals, inclu ding man, birds and amphibians. However, there is no information conce rning this morphogenetic process in fishes. A study carried out in emb ryos of the dogfish (Scyliorhinus canicula) showed that, in this elasm obranch species, the precursors of the epicardium originate from two m esothelial anlagen, the right and left, that initially lie at the vent rolateral parts of the liver. These two anlagen, which will be referre d to as the proepicardium, later shift to the right and left parts of the pericardial aspect of the transverse septum. The proepicardium com prises numerous spheric, smooth-contoured cells and a relatively small amount of extracellular matrix. The proepicardium is not covered by a n epithelial layer. Cells detaching from the proepicardium adhere to t he surface of the heart and develop into epicardial cells. They firstl y ensheathe the atrioventricular groove as well as the dorsal and late ral aspects of the ventricle, and the ventral and lateral aspects of t he atrium. Both the sinus venosus aad conus arteriosus become lined la ter. In spite of the phylogenetic distance between elasmobranchs and m ammals, the mechanism by which the epicardium develops is similar in b oth groups. This similarity relies principally on the arrangement and location of the proepicardium and the way in which the epicardial prec ursors reach and invest the heart. (C) 1997 The Royal Swedish Academy of Sciences.