The coding region of the hamster desmin gene was fused to the 5' flanking sequences of the hamster vimentin gene and introduced into the germ line of mice. The expression of this intermediate filament gene construct (pVDes) was analyzed at the RNA and protein level in transgenic mice as well as in fibroblast cell lines and primary hepatocyte cultures derived from these mice. In all transgenic mice, the pVDes-encoded protein was coexpressed with mouse vimentin in a tissue-specific fashion and was indistinguishable from normal hamster desmin. Culturing of transgenic hepatocytes induced desmin expression indicating that 3.2 kbp of the vimentin gene 5' region regulates both tissue-specific and tissue culture-induced intermediate filament protein expression. Immunohistochemical staining and double-label immunoelectron microscopy of cultured transgenic fibroblasts showed that the pVDes protein assembled into intermediate filaments which colocalized with the mouse vimentin filaments. Endogenous vimentin RNA levels were not influenced by high-level pVDes expression. The coexpression of desmin and vimentin in nonmuscle cells did not result in detectable developmental, morphological, or physiological abnormalities.

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