Yamamoto Behavior Genes Project, ERATO, c/o Mitsubishi Kasei Institute of Life Sciences, 11 Minami-ooya Machida-shi, Tokyo 194, Japan. Tel: 81-427-21-2334 Fax: 81-427-21-2850 E-mail: hiroki@fly.erato.jrdc.go.jp
We have screened about 2,000 fly lines with single P-element insertions for altered sexual behavior and isolated a mutant named satori (sat; nirvana in Japanese). The sat males never court females nor copulate, but court other males. The sat mutation comaps with fruitless (fru) at 91B, and does not complement the bisexual phenotype of fru, indicating that the sat is allelic to fru (frusat). The frusat adult males lack a male-specific muscle, the muscle of Lawrence, as do adult males in other fru alleles.
Molecular cloning and analyses of the genomic and complementary DNAs indicated that the fru gene spans over 90kb in the genome and that the P-element insertion in the frusat mutant locates in a large intron of it. Sequencing the fru cDNA clones revealed a long open reading frame that potentially encodes a putative transcription factor with a BTB domain and two zinc finger motifs. In the 5' untranslated region, three putative binding sites for the transformer (tra) protein were identified in a female transcript but not in male transcripts. In situ hybridization analyses revealed that the fru gene is expressed in a population of adult brain cells, including those in the antennal lobe.
We suggest that the fru gene controls the sexual differentiation of some neural cells downstream of tra in the sex-determination cascade and that inappropriate development of these cells in the frusat mutant leads to the altered sexual orientation.