Abstract
Ovulation is an essential physiological process in sexual reproduction; however, the underlying cellular mechanisms are poorly understood. We have previously shown that OAMB, a Drosophila G-protein-coupled receptor for octopamine (the insect counterpart of mammalian norepinephrine), is required for ovulation induced upon mating. OAMB is expressed in the nervous and reproductive systems and has two isoforms (OAMB-AS and OAMB-K3) with distinct capacities to increase intracellular Ca2+ or intracellular Ca2+ and cAMP in vitro. Here, we investigated tissue specificity and intracellular signals required for OAMB's function in ovulation. Restricted OAMB expression in the adult oviduct epithelium, but not the nervous system, reinstated ovulation in oamb mutant females, in which either OAMB isoform was sufficient for the rescue. Consistently, strong immunoreactivities for both isoforms were observed in the wild-type oviduct epithelium. To delineate the cellular mechanism by which OAMB regulates ovulation, we explored protein kinases functionally interacting with OAMB by employing a new GAL4 driver with restricted expression in the oviduct epithelium. Conditional inhibition of Ca2+/Calmodulin-dependent protein kinase II (CaMKII), but not protein kinase A or C, in the oviduct epithelium inhibited ovulation. Moreover, constitutively active CaMKII, but not protein kinase A, expressed only in the adult oviduct epithelium fully rescued the oamb female's phenotype, demonstrating CaMKII as a major downstream molecule conveying the OAMB's ovulation signal. This is consistent with the ability of both OAMB isoforms, whose common intracellular signal in vitro is Ca2+, to reinstate ovulation in oamb females. These observations reveal the critical roles of the oviduct epithelium and its cellular components OAMB and CaMKII in ovulation. It is conceivable that the OAMB-mediated cellular activities stimulated upon mating are crucial for secretory activities suitable for egg transfer from the ovary to the uterus.
Highlights
Mating activates highly coordinated physiological processes in the Drosophila female
Either OAMB isoform is sufficient to rescue defective ovulation in oamb females We have previously shown that females lacking both K3 and AS OAMB isoforms are defective in ovulation [9]
These data demonstrate that both K3 and AS are capable of reinstating normal ovulation in oamb females and suggest that OAMB expressed at the adult stage plays a significant role for this activity
Summary
Mating activates highly coordinated physiological processes in the Drosophila female. The female receives somatosensory stimulation, sperm and seminal proteins from the male. These mating signals act at multiple sites in the mated female to activate post-mating responses required for successful reproduction [1,2]. The seminal protein Ovulin stimulates egg-laying for 1 day after mating [3]. The seminal sex peptides Acp70A and DUP99B reduce sexual receptivity and stimulate egg-laying [6]. While sex peptides have widespread binding sites in the central nervous system, endocrine glands, and reproductive tissues in the female [7], it is the sex peptide receptor SPR in the neurons expressing the sex determination factor Fruitless that is indispensable for reduced receptivity as well as increased egg-laying [8]
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