Is sex determination in germ line and soma controlled by separate genetic mechanisms? Since males do not have any available Sxl protein when the late promoter is activated, their new Sxl transcripts are processed in the male manner Keyes et al. Positive autoregulation of sex-lethal by alternative splicing maintains the female determined state in Drosophila. This can happen when an X chromosome is lost from one embryonic nucleus. Loss-of-function mutations in most of these genes—Sex-lethal Sxl , transformer tra , and transformer-2 tra2 —transform XX individuals into males.
Sxl binds to a specific uridine -rich sequence which is believed to be the major cis-acting element for the splicing regulation of the transformer tra mRNA precursor . Autosomal mutations that interfere with sex determination in somatic cells of Drosophila have no direct effect on the germline. In tra, the second exon of the nonspecific mRNA has the termination codon. Mutations in the tra target gene fruitless fru , which is expressed in the antennal lobe as well as the suboesophageal ganglion the gustatory inputs are processed here , also induce homosexual courtship in males . A ratio are responsible for activating the feminizing switch gene Sex-lethal Sxl. Expression of the female form of dsx, Dsx F , in XY animals also induced germline expression of female markers. This indicates that female-specific somatic dsx products feminize XX germ cells, and male-specific somatic dsx products masculinize XX and XY germ cells. The sex-lethal gene as the pivot for sex determination Interpreting the x: Several genes with roles in sex determination have been found. Sex determination in the germ line of Drosophila melanogaster: Sex determination in the germ line of Drosophila depends on genetic signals and inductive somatic factors. Sinauer Associates ; However, expression of mini-white, the marker gene used in both P[GAL4] and P[UAS G ] constructs, also induces males to court other males, questioning whether GAL4-mediated tra expression alone can induce bisexual behavior . Normally, flies have either one or two X chromosomes and two sets of autosomes. Bell and colleagues have shown that there are two targets for the female-specific Sxl protein. Normal female germ cell differentiation requires the female X chromosome to autosome ratio and expression of sex-lethal in Drosophila melanogaster. The male Sxl mRNA is nonfunctional. This female-specific protein interacts with the Tra2 splicing factor to cause the doublesex pre-mRNA to be spliced in a female-specific manner. Physical interactions of tra Moreover, we find that female Sxl -encoded protein binds specifically to the tra transcript at or near the non-sex-specific acceptor site, implying that the female Sxl gene product is the trans-acting factor that regulates the alternative splicing . Many of these proteins have other roles during development. Its splicing is regulated by Sxl and unaffected by tra Tra and tra-2 thus promote the female specific splice rather than inhibit the male specific splice. These regions are similar to regions found in nuclear RNA-binding proteins. Much of this research has focused on the identification and analysis of the genes that are necessary for sexual differentiation and the placement of those genes in a developmental sequence. The somatic sex determines the requirement for ovarian tumor gene activity in the proliferation of the Drosophila germline. This difference is the result of differential RNA processing. This exon is not utilized in the female-specific message see Figure
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