The Octopamine Receptor Octβ2R Regulates Ovulation in Drosophila melanogaster

Abstract

Oviposition is induced upon mating in most insects. Ovulation is a primary step in oviposition, representing an important target to control insect pests and vectors, but limited information is available on the underlying mechanism. Here we report that the beta adrenergic-like octopamine receptor Octβ2R serves as a key signaling molecule for ovulation and recruits protein kinase A and Ca2+/calmodulin-sensitive kinase II as downstream effectors for this activity. We found that the octβ2r homozygous mutant females are sterile. They displayed normal courtship, copulation, sperm storage and post-mating rejection behavior but were unable to lay eggs. We have previously shown that octopamine neurons in the abdominal ganglion innervate the oviduct epithelium. Consistently, restored expression of Octβ2R in oviduct epithelial cells was sufficient to reinstate ovulation and full fecundity in the octβ2r mutant females, demonstrating that the oviduct epithelium is a major site of Octβ2R’s function in oviposition. We also found that overexpression of the protein kinase A catalytic subunit or Ca2+/calmodulin-sensitive protein kinase II led to partial rescue of octβ2r’s sterility. This suggests that Octβ2R activates cAMP as well as additional effectors including Ca2+/calmodulin-sensitive protein kinase II for oviposition. All three known beta adrenergic-like octopamine receptors stimulate cAMP production in vitro. Octβ1R, when ectopically expressed in the octβ2r’s oviduct epithelium, fully reinstated ovulation and fecundity. Ectopically expressed Octβ3R, on the other hand, partly restored ovulation and fecundity while OAMB-K3 and OAMB-AS that increase Ca2+ levels yielded partial rescue of ovulation but not fecundity deficit. These observations suggest that Octβ2R have distinct signaling capacities in vivo and activate multiple signaling pathways to induce egg laying. The findings reported here narrow the knowledge gap and offer insight into novel strategies for insect control.

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).…”

Trace Amines and Their Receptors

“…Among these effects are enhanced locomotion and flight muscle performance (Pribbenow and Erber, 1996;Saraswati et al, 2004;Fussnecker et al, 2006;Bloch and Meshi, 2007;Vierk et al, 2009), both direct and indirect mobilization of fat stores (Roeder, 2005), as well as increases in cardiac and respiratory rates (Zornik et al, 572 Gainetdinov et al 1999). OCT-mediated regulation of immune responses (Huang et al, 2012) and a role in reproductive behavior have also been reported (Lee et al, 2003;Lim et al, 2014). In the firefly, OCT is well established to underlie the neural basis of light emission (Copeland and Robertson, 1982;Christensen et al, 1983;Hashemzadeh et al, 1985) and also regulates bioluminescent emissions in glow worms (Rigby and Merritt, 2011).…”