Development of the epicardium in the dogfish (Scyliorhinus canicula)

The development of the epicardium has been described in mammals, including man, birds and amphibians. However, there is no information concerning this morphogenetic process in fishes. A study carried out in embryos of the dogfish (Scyliorhinus canicula) showed that, in this elasmobranch species, the precursors of the epicardium originate from two mesothelial anlagen, the right and left, that initially lie at the ventrolateral parts of the liver. These two anlagen, which will be referred to as the proepicardium, later shift to the right and left parts of the pericardial aspect of the transverse septum. The proepicardium comprises numerous spheric, smooth-contoured cells and a relatively small amount of extracellular matrix. The proepicardium is not covered by an epithelial layer. Cells detaching from the proepicardium adhere to the surface of the heart and develop into epicardial cells. They firstly ensheathe the atrioventricular groove as well as the dorsal and lateral aspects of the ventricle, and the ventral and lateral aspects of the atrium. Both the sinus venosus aad conus arteriosus become lined later. In spite of the phylogenetic distance between elasmobranchs and mammals, the mechanism by which the epicardium develops is similar in both groups. This similarity relies principally on the arrangement and location of the proepicardium and the way in which the epicardial precursors reach and invest the heart. (C) 1997 The Royal Swedish Academy of Sciences.