In our clonal-analysis based EMS mutagenesis screen to identify the factors involved in the early stages of germ cell development in Drosophila, we isolated an interesting mutant line.It led to a dramatic loss of germ cells when the mutant clones were generated within an otherwise heterozygous background,indicating a nonautonomous effect.We have designated the mutant as gll (germline loss) and narrowed down the disruption to 3 candidate genes.The possibility of general cell lethality is excluded, given that the mutant animal was homozygous viable with normal testis.We examined the male gonads carrying germline gll-/-clones and found that germ cell loss occurred between 2nd to 3rd instar larval stage.At present, we are tracking down the responsible gene and trying to reveal how gll contributes to the homeostasis of adult germline cells and elucidate the molecular mechanism underlying this intriguing phenotype.