Spatial, temporal, and sexually dimorphic expression patterns of the fruitless gene in the Drosophila central nervous system

The fruitless (fru) gene of Drosophila produces both sex‐specifically and non–sex‐specifically spliced transcripts. Male‐specific fru products are believed to regulate male courtship. To further an understanding of this gene's behavioral role, we examined the central nervous system (CNS) for temporal, spatial, and sexually dimorphic expression patterns of sex‐specific fru products by in situ hybridization and immunohistochemistry. For the latter, antibodies were designed to detect only male‐specific forms of the protein (FRUM) or amino acid sequences that are in common among all translated products (FRUCOM). Sex‐specific mRNAs and male‐specific proteins were first observed in mature larvae and peaked in their apparent abundances during the first half of the pupal period. At later stages and in adults, faint mRNA signals were seen in only a few neural clusters; in contrast, relatively strong FRUM signals persisted into adulthood. Twenty neuronal groups composed of 1700 fru‐expressing neurons were identified in the midpupal CNS. These groups overlap most of the neural sites known to be involved in male courtship. Anti‐FRUCOM led to widespread labeling of neural and nonneural tissues in both sexes, but in the female CNS, only in developing ganglia in a pattern different from that of the male's FRUM cells. Expression of sex‐specific fru mRNAs in the CNS of males analyzed from the earliest pupal stages indicated that sex‐specific alternative splicing is not the exclusive mechanism regulating expression of fruitless transcripts. © 2000 John Wiley & Sons, Inc. J Neurobiol 43: 404–426, 2000