Desmin and vimentin are intermediate filaments that play crucial roles in the maturation, maintenance and recovery of muscle fibers and mesenchymal cells. The expression of these proteins has not been investigated extensively in human fetuses. In the present study, we examined the immunohistochemical expression of intermediate filaments in skeletal muscles of the head, neck and thorax in 12 mid-term human fetuses at 9-18 weeks of gestation. We also used immunohistochemistry to localize the expression of the myosin heavy chain and silver impregnation to identify the fetal endomysium. Expression of desmin and vimentin was already detectable in intercostal muscle at 9 weeks, especially at sites of muscle attachment to the perichondrium. At this stage, myosin heavy chain was expressed throughout the muscle fibers and the endomysium had already developed. Beginning with punctate expression, the positive areas became diffusely distributed in the muscle fibers. At 15-18 weeks, intermediate filament proteins were extensively expressed in all of the muscles examined. Expression at the bone-muscle interface was continuous with expression along the intramuscular tendon fibres. These results suggest that the development of intermediate filaments begins in areas of mechanical stress due to early muscle contraction. Their initially punctate distribution, as observed here, probably corresponds to the earliest stage of fetal enthesis formation.

Fibroblasts exist in the interstices of various organs as a component of connective tissue and are one of several types of somatic cells that have been well established in culture. They have been reported to undergo myogenic conversion and to induce the expression of genes associated with pluripotency. However, their own plasticity with regard to direct differentiation has scarcely been described. Here, we show that human fibroblasts are able to differentiate directly to all three germ layer derivatives. The results indicate that human dermal fibroblasts have more plasticity than has been generally thought and that fibroblasts have potential utility as a source for cell therapy.

Abstract:We attempted to produce a muscle-specific cell marker, which would be useful for examining myogenesis, by introducing pMGN(-4k)LacZ-neo gene into ESD3 cells, and expression of the transgene was analyzed in embryoid bodies. The gene expression analysis of embryoid bodies indicated that transfected cells did not express LacZ gene in an undifferentiated state and that the number of cells with LacZ expression increased progressively. In DMSO treated embryoid bodies, the number of cells expressing LacZ gene tended to increase more rapidly than that of untreated ones. The results suggested that the DMSO may induce mesodermal differentiation of ES cells and that the sublines obtained might be useful as muscle-specific cell markers since they might express lacZ gene at the time of myogenin expression.

Abstract. The mouse myogenin gene regulatory region carrying the β-galactosidase (LacZ) gene was fused to a neomycin resistant gene, and introduced into ESD3 embryonic stem (ES) cells by electroporation. Transfected cells were expanded, and Southern hybridization was performed using the LacZ DNA sequence as a probe. The sublines of transformed cells were selected by karyotype analysis and by their ability to form embryoid bodies (EBs); some sublines were used for analysis of the transgene expression. The transgene was not expressed by the transformed cells in an undifferentiated state. In suspended EBs produced in hanging drops, the transgene was expressed within certain limited parts of the EBs. In some EBs, the transgene was expressed as patches in the edge of simple embryoid bodies (SEBs) and in the inner wall of cystic embryoid bodies (CEBs). In the differentiation culture system, the transgene was expressed at a cellular level, and polarization of the cells which expressed LacZ was observed. The results suggest that our sublines could be useful as skeletal muscle-specific cell markers for analysis of mouse myogenesis.

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