Failure of W/Wv mouse-derived cultured mast cells to enter S phase upon contact with NIH/3T3 fibroblasts

Although W/Wv mutant mice are profoundly deficient in tissue mast cells, these mice do have cells with similar features of mast cells that develop from their bone marrow cells as efficiently as those from congenic +/+ mice in pokeweed mitogen-stimulated spleen cell- conditioned medium (PWM-SCM). With cultured mast cells (CMCs), we analyzed the mechanism of mast-cell deficiency in tissues of W/Wv mice. CMCs were established from bone marrow cells of W/Wv and congenic +/+ mice with PWM-SCM, and then co-cultured with various mouse fibroblast cell lines without PWM-SCM. All the examined mouse embryo-derived fibroblast cell lines maintained CMCs derived from +/+ mice, but not CMCs from W/Wv mice, for greater than 2 weeks. Mast cells in S phase were observed only in CMCs derived from +/+ mice under these conditions. The poor survival of W/Wv CMCs as compared with +/+ CMCs was not owing to a differential death rate but to the inability of W/Wv CMCs to continue active proliferation on fibroblasts without PWM-SCM. By synchronizing CMCs at the G1 phase of the cell cycle, the defect in W/Wv CMCs was further characterized as a failure to transit G1 and enter the S phase upon contact with fibroblasts. This finding indicates the indispensable function of the W gene product(s) for this response.