MOLECULAR ANALYSIS OF SMOOTH-MUSCLE DEVELOPMENT IN THE MOUSE

Little is currently known regarding the ontogeny of smooth muscle tiss ues during normal mammalian development. The a-smooth muscle and gamma -smooth muscle isoactins have been shown to be excellent molecular mar kers of smooth muscle cell phenotype. This study characterizes both th e temporal and spatial patterns of or-smooth muscle and gamma-smooth m uscle isoactin expression in the developing mouse. In situ analysis wa s performed on serial sections of whole mouse embryos on embryonic day 9, 11, 13, 15, and 17 using alpha-smooth muscle and gamma-smooth musc le isoactin-specific riboprobes. Distinct temporal and spatial pattern s of a-smooth muscle and gamma-smooth muscle isoactin gene expression were observed in the developing gastrointestinal tract, urogenital tra ct, respiratory tract, and vascular system. Independent expression of the or-smooth muscle isoactin was observed during the early stages of skeletal, cardiac, and smooth muscle myogenesis as well as in a novel subset of distinct organs including the postanal component of the hind gut, allantois, and primitive placenta. The results of this study indi cate that distinct cellular phenotypes are involved in smooth muscle m yogenesis and suggest that organ-specific mechanisms might exist for t he initiation of smooth muscle development in vivo. In addition, the p attern of independent or-smooth muscle isoactin expression observed in this study provides novel information regarding the early stages of h indgut and placental development, and suggests that a common functiona l phenotype may be associated with the early stages of skeletal, cardi ac, and smooth muscle myogenesis. (C) 1995 Wiley-Liss, Inc.