Growth Competition between W Mutant and Wild-type Cells in Mouse Aggregation Chimeras

The dominant spotting (W) locus of the mouse has been demonstrated to be identical with the c-kit proto-oncogene. The c-kit is strongly expressed in hematopoietic organs and the brain of mice. In homozygotes and double heterozygotes of the W mutant alleles (hereafter W mutant), development of erythrocytes, mast cells, melanocytes and germ cells is deficient. The deficiency of erythrocytes, mast cells and melanocytes is attributed to a defect of precursor cells, but the cause of the germ cell deficiency is not clear. We investigated the effect of the W mutation on proliferative potential of cells composing various organs by examining aggregation chimeras between W mutant and wild-type (+/+) embryos. Proportions of +/+ components were significantly greater in the male germ cells and hematopoietic cells. In contrast, the average proportions of +/+ components were comparable to those of W mutant components in other organs including the brain. The present result suggests that the W (c-kit ) gene plays an important role in development of the male germ cells and hematopoietic cells and that it does not promote the proliferation of major cell population in the brain, in spite of the strong expression of the W (c-kit ) gene in the brain.