Genetic analysis of somatic sex determination in Drosophila: Regulation of Sex-lethal
Sex-lethal (Sxl) occupies a key position in the gene regulatory hierarchy of sex determination in Drosophila melanogaster. Correct regulation of Sxl is required for viability due to its role in the regulation of dosage compensation. Sxl has been referred to as a binary switch gene; ON directs female development and OFF directs male development. Sxl activity is regulated in response to the ratio of X chromosomes to Autosomes, which is the primary signal for sex determination in Drosophila. The regulation of Sxl is complex. Establishment of Sxl activity in females requires at least two distinct regulatory steps: transcriptional regulation and alternative splicing regulation. The genes involved in this complex regulation are the topic of this work. The snf gene is known to be a positive regulator of Sxl activity. snf and Sxl display a female lethal synergistic interaction. Molecular analysis of the basis of this interaction revealed that maternal snf activity is utilized for the establishment of the female-specific splicing pattern of Sxl (and not for the earlier transcriptional regulation). Therefore, under circumstances of reduced Sxl activity, both snf and the early SXL protein are required to establish the alternative splicing regulation of Sxl. A screen was designed to identify new sex determination genes involved in the regulation of Sxl. From 51,500 chromosomes screened, two mutational lines were identified and each carried two linked mutations. This screen identified a new allele of the virilizer locus (2-104.1), an allele of the l(2)49Db lethal locus (2-69.1) and two novel loci, named E(snf) (2-67.2) and E(vir) (2-97.4). In each line one mutation could dominantly suppress the male lethality of the snf1621 SxlM1 chromosome on its own (virilizer and E(snf)), and the other mutation enhanced this suppression. The virilizer (vir) mutation isolated is a temperature sensitive female sterile and female semi-lethal. E(vir) has no apparent phenotype other than its enhancement of vir. Together these mutations have striking sex-specific effects. In females they result in female sterility at 25°C and female lethality at 29°C. In males, the E(vir) vir homozygous mutant combination can effectively rescue SxlM4 male lethality. These phenotypes indicate that these genes play an important role in the regulation of Sxl. The recessive lethal mutations I(2)49Db and E(snf) interact, suggesting that the loci may be functionally related. Both of these mutations enhance snf phenotypes. This observation suggests that the E(snf) and I(2)49Db mutations identify sex determination genes, possibly in the same part of the regulatory pathway as snf.
School:Case Western Reserve University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:genetic analysis somatic sex determination drosophila regulation lethal
Date of Publication:01/01/1994