Neuropeptide Action in Insects and Crustaceans

Abstract

Physiological processes are regulated by a diverse array of neuropeptides that coordinate organ systems. The neuropeptides, many of which act through G protein–coupled receptors, affect the levels of cyclic nucleotides (cAMP and cGMP) and Ca2+ in target tissues. In this perspective, their roles in molting, osmoregulation, metabolite utilization, and cardiovascular function are highlighted. In decapod crustaceans, inhibitory neuropeptides (molt-inihibiting hormone and crustacean hyperglycemic hormone) suppress the molting gland through cAMP- and cGMP-mediated signaling. In insects, the complex movements during ecdysis are controlled by ecdysis-triggering hormone and a cascade of downstream neuropeptides. Adipokinetic/hypertrehalosemic/hyperprolinemic hormones mobilize energy stores in response to increased locomotory activity. Crustacean cardioacceleratory (cardioactive) peptide, proctolin, and FMRFamide-related peptides act on the heart, accessory pulsatile organs, and excurrent ostia to control hemolymph distribution to tissues. The osmoregulatory challenge of blood gorging in Rhodnius prolixus requires the coordinated release of serotonin and diuretic and antidiuretic hormones acting on the midgut and Malpighian tubules. These studies illustrate how multiple neuropeptides allow for flexibility in response to physiological challenges.

Molt regulation in green and red color morphs of the crab,Carcinus maenas: gene expression of molt-inhibiting hormone signaling components

“…By contrast, CHH is expressed in a wide variety of tissues including the XO/SG complex (Webster et al, 2012). Both neuropeptides share similar highly conserved motifs (reviewed by Nakatsuji et al, 2009;Webster et al, 2012) and inhibit ecdysteroid synthesis via cGMP-dependent signaling pathways (reviewed by Covi et al, 2009;Mykles et al, 2010). CHH is a pleiotropic neuropeptide that regulates glucose utilization, molting, osmoregulation and metabolism (reviewed by Chung et al, 2010;Fanjul-Moles, 2006;Webster et al, 2012).…”

Nitric oxide production and sequestration in the sinus gland of the green shore crab, Carcinus maneas

“…Sequestration of NO during intermolt would reduce NO release, resulting in elevated MIH secretion from the SG. The higher frequency and amount of MIH release would keep the YO in the basal state (Chung and Webster, 2003;Mykles et al, 2010;Chang and Mykles, 2011;Covi et al, 2012). The hypothesis predicts that NO release increases during pre-molt, resulting from increased NOS activity, decreased NO sequestration, or a combination of the two.…”

“…The episodic release of MIH may be regulated by a NO/cGMPdependent feedback mechanism. NO sequestration during inter-molt may dampen the feedback mechanism, thus increasing MIH pulses to maintain the YO in the basal state during inter-molt (Mykles et al, 2010;Chang and Mykles, 2011;Covi et al, 2012). Increased NO release due to increased NOS activity and/or decreased NO sequestration enhances the negative feedback loop.…”

“…In insects, prothoracicotropic hormone (PTTH)-induced stimulation of the molting gland (prothoracic gland or PG) requires NOS activation (Cáceres et al, 2011;Rewitz et al, 2013). In the molting gland or Y-organ (YO) of the blackback land crab Gecarcinus lateralis, NO donors and YC-1, an agonist of NO-dependent guanylyl cyclase (GC-I), inhibit ecdysteroidogenesis in YO and NOS becomes phosphorylated in the activated YO, which suggests that NOS and GC-I are components of a signaling pathway activated by moltinhibiting hormone (MIH) (Mykles et al, 2010;Chang and Mykles, 2011;Covi et al, 2012). MIH is a neuropeptide that represses the YO to maintain the animal in the intermolt stage; a reduction in MIH release is believed to result in the de-repression of steroidogenesis by the YO (Skinner, 1985;Lachaise et al, 1993;Chang and Mykles, 2011).…”

Evaluation of potential reference genes for real-time qPCR analysis in a biparental beetle, Lethrus apterus (Coleoptera: Geotrupidae)

“…The technical revolution of molecular biology and genetics, however, made it attainable to discover the details of genetic and hormonal regulation in insects (Raikhel, Brown & Belles, 2005). Some of the processes controlled by hormones mentioned above, such as ecdysis (Mykles et al, 2013) are already well described. Nevertheless, there are many interesting physiological and behavioural mechanisms, like parental care, the hormonal regulation of which are not well understood (Panaitof et al, 2016).…”