Developmentally regulated expression of Smad3, Smad4, Smad6, and Smad7 involved in TGF-beta signaling.

Transforming growth factor-beta (TGF-beta) signaling is mediated from serine/threonine kinase receptors to transcriptional responses via Smad proteins. Here comparison of mRNA expression of Smad3-7 in mouse embryos (E9-E15) revealed developmentally regulated distinct expression patterns for Smad3, 4, 6, and 7. Smad3 was prominently expressed in the differentiating (from E10) central nervous system, but also in developing bones, branchial arches and epithelium of various tissues. Smad4 mostly showed ubiquitous expression, but in E15 embryos, a pronounced signal appeared in epithelial crypts of the gut. Inhibitory Smad6 and Smad7 were coexpressed at high levels in developing cardiovascular system from the earliest stages studied. In contrast, Smad6 was selectively expressed at high levels, e.g. in intramembranous bone whereas Smad7 was prominent in seminiferous tubules of the testis, demonstrating distinct expression of these genes in non-cardiovascular tissues.