TRANSFORMATION OF THE GERM-LINE INTO MUSCLE IN MES-1 MUTANT EMBRYOS OF C-ELEGANS

Mutations in the maternal-effect sterile gene mes-1 cause the offsprin g of homozygous mutant mothers to develop into sterile adults, Lineage analysis revealed that mutant offspring are sterile because they fail to form primordial germ cells during embryogenesis, In wild-type embr yos, the primordial germ cell P-4 is generated via a series of four un equal stem-cell divisions of the zygote. mes-1 embryos display a prema ture and progressive loss of polarity in these divisions: P-0 and P-1 undergo apparently normal unequal divisions and cytoplasmic partitioni ng, but P-2 (in some embryos) and P-3 (in most embryos) display defect s in cleavage asymmetry and fail to partition lineage-specific compone nts to only one daughter cell. As an apparent consequence of these def ects, P-4 is transformed into a muscle precursor, like its somatic sis ter cell D, and generates up to 20 body muscle cells instead of germ c ells, Our results show that the wild-type mes-1 gene participates in p romoting unequal germ-line divisions and asymmetric partitioning event s and thus the determination of cell fate in early C. elegans embryos.