THE MULTI SEX COMBS GENE OF DROSOPHILA-MELANOGASTER IS REQUIRED FOR PROLIFERATION OF THE GERMLINE

We present a genetic analysis showing that the Drosophila melanogaster gene multi sex combs (mxc; Santamaria and Randsholt 1995) is needed f or proliferation of the germline. Fertility is the feature most easily affected by weak hypomorphic mutations of this very pleiotropic locus . Pole cell formation and early steps of gonadogenesis conform to the wild-type in embryos devoid of zygotic mxc(+) product. mxc mutant gona d phenotypes and homozygous mxc germline clones suggest a role for mxc (+) in control of germ cell proliferation during the larval stages, mx c(+) requirement is germ cell autonomous and specific in females, whil st in males mxc(+) product is also needed in somatic cells of the gona ds. Al though mxc can be classified among the Polycomb group (Pc-G) of genes, negative trans-regulators of the ANT-C and BX-C gene complexes , germline requirement for mxc appears independent of a need for other Pc-C gene products, and mxc gonad phenotypes are different from those induced by mutations in BX-C genes. We discuss the possible functions of the mxc(+) product which helps to maintain homeotic genes represse d and prevents premature larval haemocyte differentiation and neoplasi c overgrowth, but promotes growth and differentiation of male and fema le gonads.