PHENOTYPIC AND MOLECULAR ANALYSIS OF MES-3, A MATERNAL-EFFECT GENE REQUIRED FOR PROLIFERATION AND VIABILITY OF THE GERM-LINE IN C-ELEGANS

mes-3 is one of four maternal-effect sterile genes that encode materna l components required for normal postembryonic development of the germ line in Caenorhabditis elegans. mes-3 mutant mothers produce sterile progeny, which contain few germ cells and no gametes. This terminal ph enotype reflects two problems: reduced proliferation of the germ line and germ cell death. Both the appearance of the dying germ cells and t he results of genetic tests indicate that germ cells in mes-3 animals undergo a necrotic-like death, not programmed cell death. The few germ cells that appear healthy in mes-3 worms do not differentiate into ga metes, even after elimination of the signaling pathway that normally m aintains the undifferentiated population of germ cells. Thus, mes-3 en codes a maternally supplied product that is required both for prolifer ation of the germ line and for maintenance of viable germ cells that a re competent to differentiate into gametes. Cloning and molecular char acterization of mes-3 revealed that it is the upstream gene in an oper on. The genes in the operon display parallel expression patterns; tran scripts are present throughout development and are not restricted to g erm-line tissue. Both mes-3 and the downstream gene in the operon enco de novel proteins.