Drosophila cells that express octopamine receptors can either inhibit or promote oviposition

Abstract

Adrenergic signaling is known to play a critical role in regulating female reproductive processes in both mammals and insects. In Drosophila, the ortholog of noradrenaline, octopamine (Oa), is required for ovulation as well as several other female reproductive processes. Loss of function studies using mutant alleles of receptors, transporters, and biosynthetic enzymes for Oa have led to a model in which disruption of octopaminergic pathways reduces egg laying. However, neither the complete expression pattern in the reproductive tract nor the role of most octopamine receptors in oviposition is known. We show that all six known Oa receptors are expressed in peripheral neurons at multiple sites within in the female fly reproductive tract as well as in non-neuronal cells within the sperm storage organs. The complex pattern of Oa receptor expression in the reproductive tract suggests the potential for influencing multiple regulatory pathways, including those known to inhibit egg-laying in unmated flies. Indeed, activation of some neurons that express Oa receptors inhibits oviposition, and neurons that express different subtypes of Oa receptor can affect different stages of egg laying. Stimulation of some Oa receptor expressing neurons (OaRNs) also induces contractions in lateral oviduct muscle and activation of non-neuronal cells in the sperm storage organs by Oa generates OAMB-dependent intracellular calcium release. Our results are consistent with a model in which adrenergic pathways play a variety of complex roles in the fly reproductive tract that includes both the stimulation and inhibition of oviposition.