Cell surface characteristics of proadipocytes growth arrested at the predifferentiation GD state. Defects associated with neoplastic transformation.

The differentiation of murine proadipocytes is preceded by growth arrest at a specific state in the G1 phase of the cell cycle, designated GD. The GD arrest state has been shown to be distinct from other G1 arrest states, including those induced by serum or growth factor deprivation, designated GS, and by nutrient deprivation, designated GN. Defects in the control of growth arrest at GD have also been correlated with carcinogenesis. In this study we have analyzed the cell surface characteristics of nontransformed proadipocytes at various states in the G1 phase of the cell cycle by scanning electron microscopy. The results show that abundant cell surface microvilli, 2.0 to 4.0 micrometer long and 0.2 to 0.4 micrometer in diameter, develop when proadipocytes are cultured in medium that induces GD arrest but not when they are cultured under conditions that induce GS or GN arrest. The results also show that initiated and transformed proadipocytes fail to develop prominent cell surface microvilli when cultured in differentiation-promoting medium; they also fail to GD arrest and differentiate.