Subpopulations of fibroblasts from mouse skeletal muscle defined by clonal variation for 5′ nucleotidase expression

A primary cloning technique has been employed for the isolation of nine spontaneously transformed cell lines from mouse skeletal muscle. Four of these lines were isolated after selection for partial resistance to the purine (adenine) analog 2′6′diaminopurine and five were isolated from non‐selected control dishes. Four of the nonselected lines and three of the selected lines demonstrated a fibroblastoid morphology in vitro. The other two cell lines (one from each group) were epithelioid. Two of the three selected fibroblastoid lines were found to contain significant quantities of the enzyme 5′nucleotidase (EC3.1.3.5), whereas the four nonselected fibroblastlike lines, one selected fibroblastlike line, and the two epithelioid lines did not. In the two cell lines expressing 5′nucleotidase activity, this expression was stable in the absence of selective pressure. Histochemical staining of mouse skeletal muscle for 5′nucleotidase activity demonstrated positive staining in the cells of small blood vessels and in a subset of the connective tissue cells. The bulk of the skeletal muscle tissue, however, had no detectable 5′nucleotidase activity. We propose that the two cultivatable types of fibroblastoid cell lines represent distinct classes of fibroblastlike cells in vivo, reflecting alternative states of stable cellular differentiation involving 5′nucleotidase expression.