Proliferative quiescence of normal mast cells resembles that of cold-sensitive mutant mastocytoma cells. Dominant expression of the quiescent state in heterokaryons

Normal murine peritoneal mast cells were fused to serum-deprived, non-proliferating cells of a cultured subline (41-SB-4) of the P-815 murine mastocytoma. Upon reincubation in medium containing 10% horse serum for 48 h, mono- and binuclear 41-SB-4 cells reentered S phase of the cell cycle, while mast cell × 41-SB-4 heterokaryons as well as mono- and binuclear mast cells remained in proliferative quiescence, indicating dominant expression of the quiescent state of mast cells. The quiescent state of normal mast cells thus resembles that of cold-sensitive (cs) mutant cells (21-F) of the undifferentiated P-815 mastocytoma: at the non-permissive temperature of 33 °C, the 21-F cells were found to enter a state of quiescence which is characterized by its dominant expression in heterokaryons [1] and by morphological differentiation with the formation of metachromatically staining granules similar to those of mast cells [2]. This suggests that the cellular control mechanisms involved in entry into proliferative quiescence and in morphological differentiation of cs 21-F cells may be analogous to those of normal mast cells and/or their precursors.