Coupling of proadipocyte growth arrest and differentiation. I. Induction by heparinized medium containing human plasma.

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Abstract
The differentiation of proadipocytes in vitro typically required prolonged culture of cells at a high density in high concentrations of serum and added hormones. With such culture conditions it is difficult to design experiments to determine the mechanisms that control the differentiation process. The rapid and parasynchronous growth arrest and differentiation of low density murine proadipocytes in heparinized medium containing only human plasma is described. When low density cells are cultured under these conditions, growth arrest at a distinct state in the G1 phase of the cell cycle occurs within 2 d [day] and the differentiation of 80-100% of the cell population occurs within 4 d thereafter. The factors in human plasma which promote growth arrest and differeniation are heat labile and can be separated by barium adsorption. These methods were used to show that there are 5 separate phases which regulate the coupling of proadipocyte growth arrest and differentiation. A high cell density and extensive cell-to-cell contact, prolonged culture and high concentrations of serum and/or added hormones are not required for adipocyte differentiation.