ROLES OF THE OCTOPAMINE RECEPTOR OAMB IN ASSOCIATIVE LEARNING, MEMORY, AND REPRODUCTION IN DROSOPHILA MELANOGASTER

Open Access
Author:
Lee, Hyun-Gwan
Graduate Program:
Genetics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 12, 2008
Committee Members:
  • Kyung An Han, Committee Member
  • Richard W Ordway, Committee Member
  • Zhi Chun Lai, Committee Chair
  • Graham Hugh Thomas, Committee Member
  • David Scott Gilmour, Committee Member
Keywords:
  • octpamine receptor
  • OAMB
  • Conditioned courtship
  • Ovulation
  • CaMKII
Abstract:
Octopamine, a biogenic monoamine, is a major neuromodulator in invertebrates. It plays a crucial role in various adaptive behaviors and in female reproduction. To mediate these diverse effects, octopamine binds to specific receptors and activates distinct signal transduction pathways. The underlying intracellular mechanism, however, remains unclear. Two octopamine receptors, OAMB-K3 and OAMB-AS, are produced by alternative splicing of oamb transcripts and were distinctly characterized to activate for cAMP and intracellular calcium increases. Remarkably, both receptors are highly enriched in the mushroom bodies and the central complex of the brain, where both locations have been found to be key neural substrates for associative learning and memory. Furthermore, OAMB is expressed in the thoracico-abdominal ganglion, the female reproductive system, and mature eggs in the ovary. To explore OAMB¡¯s role in conditioned courtship as a natural form of associative learning and female reproduction, null and various hypomorphic oamb mutants were generated by P-element mediated dysgenesis. oamb null mutants were found to be viable without gross anatomical defects and oamb females displayed normal courtship and copulation behaviors. oamb null mutant males were also normal in acquisition, but were impaired in short-term memory retention for conditioned courtship behaviors. Transgenic OAMB-AS expression, driven by pan neuronal elav-GAL4, rescues the memory deficit of oamb in short-term memory retention for conditioned courtship, suggesting that neuronal OAMB-AS is crucial for this behavior. oamb null mutant females have been found to be sterile. To investigate the tissue type(s) and intracellular effectors that OAMB mediates ovulation, the GAL4/UAS binary system was employed. Transgenic oamb females, with adults ubiquitously expressing either OAMB-K3 or -AS driven by heat shock-GAL4, were fecund, indicating that OAMB plays a physiological, and not a developmental, role in ovulation. Neural OAMB expression, however, is deficient for inducing ovulation in oamb null mutant females. To identify OAMB¡¯s functional site, the enhancer GAL4 line oamb-RS-GAL4 was generated so that GAL4 could be specifically expressed in the reproductive system. Remarkably, strong oamb-RS-GAL4 expression was detectable in the oviduct epithelial cells, where endogenous OAMB is found. oamb females, with transgenic OAMB-K3 or -AS expression driven by oamb-RS-GAL4, were fully fertile, suggesting that OAMB is crucial in oviduct epithelial cells for regulating ovulation. To identify for downstream OAMB signaling molecules involved with ovulation, transgenes expressing constitutively active Ca2+/calmodulin-dependent protein kinase II (CaMKIICA), CaMKII inhibitor peptide ala, and dNOS-IR were expressed by oamb-RS-GAL4 in adult oviduct epithelial cells. Ovulation defects of oamb females were rescued by transgeneic CaMKIICA expression in adult oviduct epithelium. CaMKII inhibitor peptides ala and dNOS-IR driven by oamb-RS-GAL4, however, reduced female fecundity in a heterozygous background. Therefore, CaMKII and possibly nitric oxide are major downstream signaling molecules of OAMB for regulating ovulation. These studies provide significant insight into the physiological and cellular mechanisms involved with octopamine function in associative learning and memory as well as for the female reproductive system.