Local expression of cytokeratins 8, 17 and 18 in the mesenchyme and smooth muscles in the early stages of human organogenesis

Expression of cytokeratins 7, 8, 17, 18 in human embryos and fetuses of 6.5-13 weeks was studied using light and electron immunocytochemistry and immunoelectroblotting with the monoclonal antibodies. Cytokeratins 8 and 18 were expressed in 6.5-8 week old embryos not only in epithelium but also in mesenchyme of allantois, urogenital sinus, Wolffian and Mullerian ducts, mesentery, urinary bladder and certain regions of colon, rectum and atrium cordis walls. Furthermore, starting from the 10th week smooth-muscle cells of ring layer in caudal part of rectum bound antibodies against cytokeratin 17 in addition to those against cytokeratins 8 and 18. Corresponding mesenchymal and smooth-muscle cells of adult individuals did not react with either of them. Cytokeratins were still synthesized when mesenchymal cells of embryonic intestine wall were cultivated in vitro. Intermediate filaments of these cells contain cytokeratins 8 and 18, as demonstrated by electron immunocytochemistry and immunoelectroblotting. Thus, the expression of cytokeratins is not restricted to adult and embryonic epithelial tissues but is also characteristic of mesenchyme and smooth muscle differentiation in human embryos and fetuses.