Binding sites of Drosophila melanogaster sex peptide pheromones

ABSTRACT: Drosophila melanogaster sex peptide (SP) and Ductus ejaculatorius peptide (DUP99B) are male pheromones transferred in the seminal fluid to the female during copulation. Both reduce sexual receptivity and stimulate oviposition in females. The presence of high-affinity SP and DUP99B binding sites in the female were investigated by incubation of cryostat tissue sec-tions with 125I-iodinated peptides and subsequent auto-radiography. We found that in adult females radiola-beled SP and DUP99B bind to peripheral nerves, the subesophageal ganglion, the cervical connective, to dis-crete parts of the thoracic ganglion, and to the genital tract. Weak and uniform labeling was detected in the neuropil of the brain and the thoracic ganglion. The labeling pattern in the nervous system suggests binding of the peptides to sensory afferents or glial cells. Scat-chard analysis of the binding of 125I-DUP99B to anten-nal nerves yielded a dissociation constant Kd of 6.4 nM. Competition experiments with peptide fragments show that the peptides bind with their homologous C-terminal regions. Binding sites in the nervous system of females are established throughout sexual maturation. Promi-nent binding of the peptides to afferent nerves suggests modification of sensory input. © 2000 John Wiley & Sons, Inc