Autosomal control of lampbrush-loop formation during spermatogenesis in Drosophila hydei by a gene also affecting somatic sex determination.

The Y chromosome of Drosophila hydei carries information that is necessary for the development of the spermatozoa. In primary spermatocytes Y chromosomal genes become active: five of the male fertility factors form giant lampbrush loops. Our prior work indicated interactions between the Y chromosomal genes and autosomal loci. It is of interest to identify loci regulating the activity of the Y chromosomal genes. We, therefore, screened a total of about 14,000 chromosomes (X, 2, 3 and 4) for mutations that interfere with the expression of the lampbrush loops. Two mutations with substantial effects on the loop morphology were recovered. One of them, a recessive male sterile mutation (ms (3) 5) on chromosome 3, is described in this paper. Its homozygous state results in a complete absence of all Y chromosomal lampbrush loops at 26° C; at 18° C the loops are formed. Temperature shifts with homozygous males indicate that the function early during the spermatogonial stage is crucial for the development of lampbrush loops in the primary spermatocyte. Meiosis is entirely absent in the male, but normal in females. Females homozygous for ms (3) 5 display a maternal effect, which reduces the viability and fertility of homozygous daughters and produces sons with signs of intersexuality. Linkage studies indicated that the effect on the male germ line and the maternal effects cannot be separated and may hence be induced by a single gene.