Recruitment of the proneural gene scute to the Drosophila sex-determination pathway.
In flies, scute (sc) works with its paralogs in the achaete-scute-complex (ASC) to direct neuronal development. However, in the family Drosophilidae, sc also acquired a role in the primary event of sex determination, X chromosome counting, by becoming an X chromosome signal element (XSE)-an evolutionary step shown here to have ... occurred after sc diverged from its closest paralog, achaete (ac). Two temperature-sensitive alleles, sc(sisB2) and sc(sisB3), which disrupt only sex determination, were recovered in a powerful F1 genetic selection and used to investigate how sc was recruited to the sex-determination pathway. sc(sisB2) revealed 3' nontranscribed regulatory sequences likely to be involved. The sc(sisB2) lesion abolished XSE activity when combined with mutations engineered in a sequence upstream of all XSEs. In contrast, changes in Sc protein sequence seem not to have been important for recruitment. The observation that the other new allele, sc(sisB3), eliminates the C-terminal half of Sc without affecting neurogenesis and that sc(sisB1), the most XSE-specific allele previously available, is a nonsense mutant, would seem to suggest the opposite, but we show that housefly Sc can substitute for fruit fly Sc in sex determination, despite lacking Drosophilidae-specific conserved residues in its C-terminal half. Lack of synergistic lethality among mutations in sc, twist, and dorsal argue against a proposed role for sc in mesoderm formation that had seemed potentially relevant to sex-pathway recruitment. The screen that yielded new sc alleles also generated autosomal duplications that argue against the textbook view that fruit fly sex signal evolution recruited a set of autosomal signal elements comparable to the XSEs.
Mesh Terms:
Amino Acid Sequence, Animals, Animals, Genetically Modified, Biological Evolution, Codon, Nonsense, DNA-Binding Proteins, Drosophila, Drosophila Proteins, Female, Gene Expression Regulation, Developmental, Genes, Lethal, Male, Molecular Sequence Data, Mutagenesis, Site-Directed, Neurons, Phenotype, Regulatory Sequences, Nucleic Acid, Selection, Genetic, Sex Determination Processes, Signal Transduction, Temperature, Transcription Factors, Transcription, Genetic, Transgenes, X Chromosome
Amino Acid Sequence, Animals, Animals, Genetically Modified, Biological Evolution, Codon, Nonsense, DNA-Binding Proteins, Drosophila, Drosophila Proteins, Female, Gene Expression Regulation, Developmental, Genes, Lethal, Male, Molecular Sequence Data, Mutagenesis, Site-Directed, Neurons, Phenotype, Regulatory Sequences, Nucleic Acid, Selection, Genetic, Sex Determination Processes, Signal Transduction, Temperature, Transcription Factors, Transcription, Genetic, Transgenes, X Chromosome
Genetics
Date: Dec. 01, 2003
PubMed ID: 14704182
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