Calcium influx enhances neuropeptide activation of ecdysteroid hormone production by mosquito ovaries

Abstract

A critical step in mosquito reproduction is the ingestion of a blood meal from a vertebrate host. In mosquitoes like Aedes aegypti, blood feeding stimulates the release of ovary ecdysteroidogenic hormone (OEH) and insulin-like peptide 3 (ILP3). This induces the ovaries to produce ecdysteroid hormone (ECD), which then drives egg maturation. In many immature insects, prothoracicotropic hormone (PTTH) stimulates the prothoracic glands to produce ECD that directs molting and metamorphosis. The receptors for OEH, ILP3 and PTTH are different receptor tyrosine kinases with OEH and ILP3 signaling converging downstream in the insulin pathway and PTTH activating the mitogen-activated protein kinase pathway. Calcium (Ca2+) flux and cAMP have also been implicated in PTTH signaling, but the role of Ca2+ in OEH, ILP3, and cAMP signaling in ovaries is unknown. Here, we assessed whether Ca2+ flux affects OEH, ILP3, and cAMP activity in A. aegypti ovaries and also asked whether PTTH stimulated ovaries to produce ECD. Results indicated that Ca2+ flux enhanced but was not essential for OEH or ILP3 activity, whereas cAMP signaling was dependent on Ca2+ flux. Recombinant PTTH from Bombyx mori fully activated ECD production by B. mori PTGs, but exhibited no activity toward A. aegypti ovaries. Recombinant PTTH from A. aegypti also failed to stimulate either B. mori PTGs or A. aegypti ovaries to produce ECD. We discuss the implications of these results in the context of mosquito reproduction and ECD biosynthesis by insects generally.

Whole blood and blood components from vertebrates differentially affect egg formation in three species of anautogenous mosquitoes

“…Total ecdysteroids secreted by ovaries were quantified using an enzyme-linked immunosorbent assay (EIA) [ 10 ]. Ovaries were dissected from females 20 h after feeding, which corresponds with when ecdysteroid production peaks in ovaries after consumption of rat blood [ 8 ].…”

“…Ovaries were dissected from females 20 h after feeding, which corresponds with when ecdysteroid production peaks in ovaries after consumption of rat blood [ 8 ]. The ovaries from two females were pooled and incubated together in 60 µl Beyenbach’s saline [ 10 ] on a shaker for 6 h at 27 °C and ~90% RH. Following this incubation period, medium supernatant containing secreted ecdysteroids was collected and frozen at – 20 °C.…”

Isolation of an insulin-like peptide from the Asian malaria mosquito, Anopheles stephensi, that acts as a steroidogenic gonadotropin across diverse mosquito taxa

“…The previous in-house effort to synthesize AaILP3 was long and complicated but finally successful (Brown et al, 2008) and enabled the elucidation of its binding to the insulin receptor and diverse functions in Ae. aegypti (Wen et al, 2010; Gulia-Nuss et al, 2011; Castillo et al, 2011; Gulia-Nuss et al, 2012; Gulia-Nuss et al, 2015; McKinney et al, 2016). Fortunately, commercial peptide synthesis has advanced greatly and synthesis of AsILP3 and AsILP4 in milligram quantities was a reasonable expense, given the bioactivity and stability of the product.…”

Calcitox-aging counterbalanced by endogenous farnesol-like sesquiterpenoids: An undervalued evolutionarily ancient key signaling pathway

“…A similar system has also been observed in the mosquito Aedes aegypti . 78 These authors reported that Ca 2+ -influx enhances neuropeptide activation of ecdysteroids hormone production by mosquito ovaries.…”