The origin and function of a courtship gene, Sphinx, in Drosophila melanogaster

Origination of genes is one of the central topics in evolutionary studies. One approach to understanding the origination of genes is to study recently evolved genes, which provide relatively abundant information to reveal the early history of evolution. Sphinx (Spx), a putative chimerical RNA gene that originated in D. melanogaster about 2--3 MYA, has been investigated in this work. Evolutionary history of Sphinx has been addressed by inter- and intro-specific sequence comparison. The highly conserved upstream region of Sphinx among Drosophila species and low nucleotides diversity shared among D. melanogaster worldwide populations not only suggests the possible functional importance of this putative promoter region but also gives the possible explanation for the two consecutive exon insertion on 4th chromosome that started from the divergence between D. yakuba and D. simulans/sechellia/melanogaster subgroup. I investigated this region by tagging with GFP to create transgenic strains. I observed sex-related GFP expression in accessory gland, and also detected chemosensory-related GFP expression in labral organs, foreleg, and forefront of wings in both male and female, which suggests a role of Sphinx in the recognition behavior. I conducted gene replacement and created a splicing deficient mutant of Sphinx. I obtained the first mutant line SPX720 and verified the mutation sites. The results of RT-PCR indicate that the full transcript isoform was silenced in the mutant line, suggesting a loss-of-function mutation. Courtship behavioral studies showed that the mutant male exhibits significantly increased male-male courtship behaviors by chasing and singing to another male. I also absorbed courtship chain and courtship circle formed by multiple males following one by one were also observed. Finally, the expression microarray experiments reveal a set of genes affected by Sphinx mutant, including pheromone receptors and other behavior related genes, further confirm Sphinx might be involved in regulation of courtship behavior. All together, these data present a first case that a recent evolved gene controls courtship behaviors in single specie.