A glial amino-acid transporter controls synapse strength and courtship in Drosophila

Abstract

Mate choice is an evolutionarily critical decision that requires the detection of multiple sex-specific signals followed by central integration of these signals to direct appropriate behavior. The mechanisms controlling mate choice remain poorly understood. Here, we show that the glial amino-acid transporter genderblind controls whether Drosophila melanogaster males will attempt to mate with other males. Genderblind (gb) mutant males showed no alteration in heterosexual courtship or copulation, but were attracted to normally unappealing male species-specific chemosensory cues. As a result, genderblind mutant males courted and attempted to copulate with other Drosophila males. This homosexual behavior could be induced within hours using inducible RNAi, suggesting that genderblind controls nervous system function rather than its development. Consistent with this, and indicating that glial genderblind regulates ambient extracellular glutamate to suppress glutamatergic synapse strength in vivo, homosexual behavior could be turned on and off by altering glutamatergic transmission pharmacologically and/or genetically.

Figure 1

gb mutant males are ‘genderblind’. (a) Percentage of time that individual Drosophila males spent courting when placed together in groups of six in a test chamber (n = 12–18 males per genotype, except for gb/TM3GFPSer, where n = 6). (b) Total amount of genderblind protein, as measured by immunoblot, compared with percentage of time spent in male-male courtship, as graphed in a. Inset shows sample lanes from the same immunoblot, where the left lane was loaded with protein from wild-type (WT) male flies and the right lane was loaded with protein from gb[KG07905] flies. Shaded ovals on graph are centered on the mean for each type measurement (genderblind protein, courtship index), and the length and width of each oval represents s.e.m. Each oval is labeled with the genotype from which the measurements were obtained. (c) Percentage of time spent courting by individual wild-type or gb mutant males placed in a chamber with both a passive (decapitated) wild-type virgin female and a passive (decapitated) wild-type male (n = 12–13). (d) Percentage of time spent courting by a single wild-type or gb mutant male placed in a chamber with either a passive (decapitated) wild-type male or passive (decapitated) virgin female (n = 25–32). All error bars represent mean ± s.e.m.

Figure 2

gb mutant males show altered responses to species-specific chemical sexual cues. (a) Percentage of time that single wild-type or gb mutant males spent courting when placed in a chamber with a passive (decapitated) wild-type male under dim red light (n = 8). (b) Percentage of time that single wild-type or gb mutant males spent courting when placed in a chamber under dim red light with a passive (decapitated) desat1 mutant male that had (right) or had not (left) received topical application of pheromone 7-tricosene (n = 18–21). (c) Percentage of time that individual wild-type or gb mutant males spent courting a passive (decapitated) mated female (n= 6–11). (d) Percentage of time that passive (decapitated) virgin females of the listed species were courted by wild-type and gb mutant males (n = 10–13, except for D. virilis, n = 5). All error bars represent mean ± s.e.m.

Figure 3

Genderblind (genderblind) protein is expressed in central glia surrounding glutamatergic neurons. (a–c) Single fluorescence confocal microscopy sections from male adult brains, stained with antibodies to genderblind (magenta) and CD8 (green). Colocalization is represented by white color. For each image, the transgenic transmembrane protein CD8::GFP was expressed in a specific tissue-type using the Gal4/UAS system. CD8 expression was driven with the neuronal driver Elav-Gal4 (a), Repo-Gal4 (which is expressed in a subset of glia, b) or the weak glutamatergic neuron driver OK371-Gal4 (c). Selected brain structures are indicated in each panel. AL, antennal lobe; CA, calyx; CC, central complex; MB, mushroom body; SOG, subesophageal ganglion (see also Supplementary Fig. 3). Scale bars represent 25 μm.

Figure 4

Drosophila male homosexual courtship is controlled by the strength of glutamatergic neurotransmission. (a–f) Percentage of time that individual males spent courting when groups of six males were placed together in a test chamber (n = 12–18, except for RepoGal4, NP225Gal4, UASDVGluT, UASDVGluT;MB247Gal4 and UASDVGluT;NP225Gal4, where n = 6). All error bars represent mean ± s.e.m. (g) A model for how genderblind might regulate Drosophila sexual behavior.