deadpan, an essential pan-neural gene encoding an HLH protein, acts as a denominator in Drosophila sex determination.
In Drosophila, sex is determined by the X:A ratio. One major numerator element on the X chromosome is sisterless-b (sis-b), also called scute, which encodes an HLH-type transcription factor. We report here that an essential pan-neural gene, the autosomal HLH gene deadpan (dpn), acts as a denominator element. As revealed by dosage-dependent dominant interactions, males die with too high a ratio of sc+ to dpn+, caused by misexpression of Sex lethal (Sxl) in embryos, and females die with too low a ratio of sc+ to dpn+, because of altered embryonic Sxl expression. In addition, we found that the HLH gene extramacrochaetae (emc), like daughterless (da), is needed maternally for proper communication of the X:A ratio, thus supporting the idea that a set of HLH genes comprises a functional cassette that makes a sensitive and stable genetic switch used in both neural determination and sex determination.
Younger-Shepherd
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Howard Hughes Medical Institute, University of California, San Francisco 94143.
Vaessin
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Bier
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D000818:Animals; D002872:Chromosome Deletion; D004303:Dosage Compensation, Genetic; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D005260:Female; D005804:Genes, Lethal; D008297:Male; D005810:Multigene Family; D009420:Nervous System / Q000196:embryology; D012733:Sex Differentiation / Q000235:genetics*; D013489:Suppression, Genetic