DEVELOPMENTALLY-REGULATED NEURAL PROTEIN EAP-800 IS EXPRESSED BY MYOCARDIUM AND CARDIAC NEURAL CREST DURING CHICK EMBRYOGENESIS

The spatiotemporal distribution of EAP-300 (embryonic avian polypeptid e of 300 kDa) was analyzed in embryonic chick heart using immunohistoc hemistry and confocal microscopy. EAP-300 is a developmentally regulat ed protein initially characterized in neural cells from chick retina. Myocardial cells all along the early tubular heart were ubiquitously i mmunolabeled for EAP-300 by embryonic day 2 (E2, Stage 13)). At E5 (St age 24), myocardial EAP-300 expression levels remained significant in both atrial and ventricular myocardium. At E6 (Stage 28), distinct pop ulations of EAP-300 immunolabeled cells were also observed external to the heart, in septal mesenchymal tissue and neural ganglia adjacent t o the outflow tract; these cell populations were confirmed as neural c rest-derived by co-localization of EAP-300 and HNK-1. At E13 (Stage 39 ), myocardial immunolabeling for EAP-300 was no longer ubiquitous, but increasingly restricted to conduction tissues, including the atrioven tricular bundle and subendocardial Purkinje cells. This restriction of immunolabeling could be demonstrated definitively at E15 (stage 41), by which stage subendocardial and periarterial Purkinje fibers were cl early immunoreactive for EAP-300 and several known markers of chick co nduction tissue, including specific myosin heavy chain isoforms and co nnexin42, a gap junctional protein preferentially expressed by Purkinj e fibers. Just prior to hatching at E21 (Stage 46), immunolabeling of conduction tissues was reduced, although still above that of non-condu ctile myocardium. This spatiotemporal map of cardiac EAP-300 expressio n indicates that it is independently and transiently expressed in earl y myocardium, cardiac conduction tissue, and neural crest derivatives during development. (C) 1995 Wiley-Liss, Inc.