Abstract. The muscle-specific intermediate filament protein, desmin, is one of the earliest myogenic markers whose functional role during myogenic commitment and differentiation is unknown. Sequence comparison of the presently isolated and fully characterized mouse desmin cDNA clones revealed a single domain of polypeptide similarity between desmin and the basic and helix-loop-helix region of members of the myoD family myogenic regulators. This further substantiated the need to search for the function of desmin. Constructs designed to express anti-sense desmin RNA were used to obtain stably transfected C2C12 myoblast cell lines. Several lines were obtained where expression of the anti-sense desmin RNA inhibited the expression of desmin RNA and protein down to basal levels. As a consequence, the differentiation of these myoblasts was blocked; complete inhibition of myoblast fusion and myotube formation was observed. Rescue of the normal phenotype was achieved either by spontaneous revertants, or by overexpression of the desmin sense RNA in the defective cell lines. In several of the cell lines obtained, inhibition of desmin expression was followed by differential inhibition of the myogenic regulators myoD and/or myogenin, depending on the stage and extent of desmin inhibition in these cells. These data suggested that myogenesis is modulated by at least more than one pathway and desmin, which so far was believed to be merely an architectural protein, seems to play a key role in this process.

No abstract

There are many reports of antisense inhibition of gene expression in cultured cells. We have generated four strains of transgenic mice expressing antisense hypoxanthine guanine phosphoribosyltransferase (HPRT) RNA in brain, or heart and liver, or all three organs. In the brain of one strain, the level of antisense RNA in the different brain regions roughly correlates with the degree of inhibition of the native HPRT mRNA in those same regions. Despite this decrease of up to 60% of endogenous HPRT mRNA, no reproducible reduction in HPRT activity has been observed. Possible reasons for the differences between the effectiveness of antisense inhibition in cultured cells and transgenic animals are discussed.

No abstract