Distinct octopamine cell population residing in the CNS abdominal ganglion controls ovulation in Drosophila melanogaster

Abstract

Octopamine is an important neuroactive substance that modulates several physiological functions and behaviors of invertebrate species. Its biosynthesis involves two steps, one of which is catalyzed by Tyramine beta-hydroxylase enzyme (TBH). The Tbetah gene has been previously cloned from Drosophila melanogaster, and null mutations have been generated resulting in octopamine-less flies that show profound female sterility. Here, I show that ovulation process is defective in the mutant females resulting in blockage of mature oocytes within the ovaries. The phenotype is conditionally rescued by expressing a Tbetah cDNA under the control of a hsp70 promoter in adult females. Fertility of the mutant females is also restored when TBH is expressed, via the GAL4-UAS system, in cells of the CNS abdominal ganglion that express TBH and produce octopamine. This neuronal population differs from the dopamine- and serotonin-expressing cells indicating distinct patterns of expression and function of the three substances in the region. Finally, I demonstrate that these TBH-expressing cells project to the periphery where they innervate the ovaries and the oviducts of the reproductive system. The above results point to a neuronal focus that can synthesize and release octopamine in specific sites of the female reproductive system where the amine is required to trigger ovulation.

Two Functional but Noncomplementing Drosophila Tyrosine Decarboxylase Genes

“…We developed GAL4 drivers for each gene and examined their in vivo expression patterns by using two different UAS-GFP reporter lines: UAS-CD8-GFP, a marker reported to be highly concentrated in neural processes including axons and dendrites (24), and UAS-GFP.nls, which contains a nuclear localization signal. Previous studies have detected octopamine and TBH in distinct clusters of cells throughout the central brain and along the ventral midline of the adult thoracic nerve cord (12,25), and recent studies indicate that TBH-expressing neurons send projections through the abdominal ganglion to the female reproductive tract, where they innervate the ovaries and oviduct (12). Based on these results and our real time PCR evidence, we predicted that dTdc2 would be expressed in a similar pattern as that seen for TBH and octopamine.…”

“…These cells could either be tyramine-specific neurons or an artifact of the GAL4 driver. As described for TBH (12), dTdc2-GAL4 neurons are located along the ventral midline of the abdominal segment of the thoracic CNS and send axons into the abdominal nerve, where they project over the posterior region of the ovaries and provide heavy innervation to the calyx and to the lateral and common oviducts (Fig. 4, B-D).…”

“…10), including Drosophila female fertility. Flies that lack a functional octopamine receptor or cannot synthesize octopamine due to a null allele of tyramine ␤-hydroxylase (T␤h) 2 show a complete egg retention phenotype (11)(12)(13). The sterility of T␤h null females is due to a defect in ovulation, which can be rescued by octopamine feeding or by driving the ectopic expression of a T␤h transgene in several driver lines that show overlapping expression in the thoracic tip of the CNS (12,13).…”

A Systematic Analysis of Drosophila Gustatory Receptor Gene Expression in Abdominal Neurons which Project to the Central Nervous System

“…In studies on Drosophila ovulation, female postmating behavior, and male courtship or reproductive behavior (Hasemeyer et al, 2009;Lee et al, 2001;Monastirioti, 2003;Yang et al, 2009), abdominal peripheral neurons were observed to directly project to the abdominal ganglion to mediate diverse functions. Therefore, although it is not yet clear what functions the Grs are mediating in the multidendritic neurons and reproductive organs, it seems likely that the information sensed by the Grs in these organs is conveyed to the abdominal ganglion to be processed.…”

Steroid signaling in mature follicles is important for Drosophila ovulation

“…This follicle rupture also relies on proteolytic enzymes, like matrix metalloproteinase 2 (Mmp2), which is specifically expressed in the posterior follicle cells of stage-14 egg chambers (9). Mmp2 activation is stimulated by the monoamine octopamine (OA), which is equivalent to norepinephrine in mammals and is essential for ovulation (10,11). OA binds to its receptor Octopamine receptor in mushroom body (Oamb) in mature follicle cells to induce an intracellular calcium rise, Mmp2 activation, and follicle rupture (12).…”