TEMPOROSPATIAL EXPRESSION OF THE SMALL HSP ALPHA-B-CRYSTALLIN IN CARDIAC AND SKELETAL-MUSCLE DURING MOUSE DEVELOPMENT/

Although the small (22 Kd) heat shock protein/alpha B-crystallin funct ions as a major structural protein and molecular chaperone in the vert ebrate lens, little is known about the protein's role in nonlenticular tissues such as the heart and skeletal muscle. Recent studies have de monstrated that alpha B-crystallin expression is uniquely regulated du ring myogenesis in vitro. We report here for the first time that the t emporal and spatial expression of alpha B-crystallin is similarly regu lated in vivo during mouse embryogenesis. Expression of alpha B-crysta llin mRNA was detected by in situ hybridization in the primitive heart at 8.5 days postconception (p.c.) and in the myotome of the somites a t 10.5 days p.c. This tissue-restricted pattern was corroborated by im munohistochemical studies. alpha B-crystallin mRNA and protein express ion were uniform in the developing atria and ventricles without region al differences or gradients. alpha B-crystallin expression was absent in the endocardial cushion, pulmonary trunk, aorta, and endothelium. E xamination of muscle precursors revealed expression throughout the dor soventral aspect of the myotomes and in developing skeletal muscle. Ou r findings suggest that alpha B-crystallin may serve pivotal roles as a structural protein and a molecular chaperone in myofiber stabilizati on of metabolically active tissues during early embryogenesis. Thus, e arly alpha B-crystallin expression in myogenic Lineages supports the h ypothesis that the putative functions of alpha B-crystallin are couple d to the activation of genetic programs responsible for myogenic diffe rentiation and cardiac morphogenesis. (C) 1997 Wiley-Liss, Inc.