THE OCTOPAMINE RECEPTOR octß2R IS ESSENTIAL FOR OVULATION AND FERTILIZATION IN THE FRUIT FLY Drosophila melanogaster

Abstract

The biogenic monoamine octopamine is essential for ovulation and fertilization in insects. Release of this hormone from neurons in the thoracoabdominal ganglion triggers ovulation and sperm release from the spermathecae. Here we show that the effects of octopamine on ovulation are mediated by at least two different octopamine receptors. In addition to the Oamb receptor that is present in the epithelium of the oviduct, the octß2R receptor is essential for ovulation and fertilization. Octß2R is widely expressed in the female reproductive tract. Most prominent is expression in the oviduct muscle and the spermathecae. Animals deficient in expression of the receptor show a severe egg-laying defect. The corresponding females have a much larger ovary that is caused by egg retention in the ovary. Moreover, the very few laid eggs are not fertilized, indicating problems in the process of sperm delivery. We assume that octß2R acts in a similar way as ß2-adrenoreceptors in smooth muscles, were activation of this receptor induces an increase in cAMP levels that lead to relaxation of the muscle. Taken together, our findings show that octopaminergic control of ovulation and fertilization is more complex than anticipated and that various receptors located in different cells act together to enable a well-orchestrated activity of the female reproductive system in response to copulation.

Octopamine and tyramine regulate the activity of reproductive visceral muscles in the adult female blood-feeding bug, Rhodnius prolixus

“…In D. melanogaster, octopamine was found to increase the contractions of the peritoneal sheath, a contractile meshwork that surrounds the ovary, and to relax the oviducts, thereby enabling the release of eggs into the oviducts (Middleton et al, 2006). Moreover, Octβ2R and OAMB have been found to be the receptors associated with the process of ovulation and fertilization in Drosophila (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). Deletions in the oamb locus and mutant constructs of Octβ2R resulted in accumulation of eggs in the ovary and a significant decrease in the number of eggs laid (Lee et al, 2003;Li et al, 2015;Lim et al, 2014).…”

“…Moreover, Octβ2R and OAMB have been found to be the receptors associated with the process of ovulation and fertilization in Drosophila (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). Deletions in the oamb locus and mutant constructs of Octβ2R resulted in accumulation of eggs in the ovary and a significant decrease in the number of eggs laid (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). Similarly, in R. prolixus, octopamine reduced the amplitude of oviduct contractions, probably by binding to OctβR, leading to an elevation in cAMP levels and muscle relaxation.…”

“…In Drosophila and the stable fly Stomoxys calcitrans, octopamine reduces the amplitude and frequency of contractions, and reduces basal tonus of the oviducts in a dose-dependent manner (Cook and Wagner, 1992;Middleton et al, 2006;Rodríguez-Valentín et al, 2006). These physiological effects could be linked to two receptors: the octopamine receptor in the mushroom bodies (OAMB) and Octβ2-R, which have been shown in Drosophila to be expressed in the epithelial and muscle cells of the oviducts (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). These receptors are involved in ovulation and fertilization of eggs, whereby mutant constructs of these receptors show reproductive sterility in females, accumulation of eggs in the ovary and reduction in the number of eggs laid (Lee et al, 2003;Li et al, 2015;Lim et al, 2014).…”

“…These physiological effects could be linked to two receptors: the octopamine receptor in the mushroom bodies (OAMB) and Octβ2-R, which have been shown in Drosophila to be expressed in the epithelial and muscle cells of the oviducts (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). These receptors are involved in ovulation and fertilization of eggs, whereby mutant constructs of these receptors show reproductive sterility in females, accumulation of eggs in the ovary and reduction in the number of eggs laid (Lee et al, 2003;Li et al, 2015;Lim et al, 2014). In contrast, octopamine has also been shown to increase the frequency and the amplitude of myogenic contractions in the lateral oviducts of the cricket Gryllus bimaculatus (Tamashiro and Yoshino, 2014).…”

Expression analysis of octopamine and tyramine receptors in Drosophila

“…Its presence in the oviduct may thus be the reason for this female sterility (Lee et al 2003). OA controls the female reproductive system at different levels, also including the octß2R, which is expressed on the oviduct muscle and the spermatheca (Lim et al 2014;Li et al 2015). Apparently, Oamb is necessary to enable liquid secretion, which is required to enable ovulation while Octß2R allows relaxation of the oviduct muscle.…”