Adipose conversion of ob17 cells. Insulin acts solely as a modulator in the expression of the differentiation program.

Adipose conversion of ob17 preadipocyte cells was studied in insulin-depleted (less than 0.2 pM), serum-supplemented medium. The results show that insulin is neither required for the commitment of stem cells ( adipoblasts ) to preadipocytes nor for the onset of the differentiation program and the post-confluent mitoses of preadipocytes to adipocyte-like cells. No unmasking of insulin 'super' receptors and no cellular production of insulin can be detected in cells exposed to insulin-depleted medium. Insulin enhances only the rate of the lipid-filling process of differentiating cells and thus the number of fat cell clusters visible after staining for neutral lipids. Therefore, in the light of these and previous results [17, 18], the role of insulin is only to act as a modulator in the expression of the differentiation program.