ob17 cells transformed by the middle-T-only gene of polyoma virus differentiate in vitro and in vivo into adipose cells.

Cell lines were derived from ob17 preadipocyte cells by focus formation after transfer of the complete early region of polyoma virus (ob17PY) or of a modified genome encoding only the middle T protein (ob17MT). Both ob17PY and ob17MT cell lines exhibited a high cloning efficiency in agarose medium containing 10% fetal bovine serum. Fully transformed ob17PY cells grew to high saturation densities and did not differentiate in vitro and in vivo. ob17MT cells and derived subclones did not grow in the absence of serum and were able to differentiate in vitro and to give rise in vivo to adipose tumors. Among these different clones an inverse relationship was observed in culture between their potentiality to overproliferate at low serum and their potentiality to convert into adipose cells. The expression of enzyme markers of adipose conversion was strictly dependent upon the presence of growth hormone. In addition, the hormonal requirements for differentiation were simpler than those of the original ob17 cells and the adipose conversion could take place in serum-free hormone-supplemented medium.