Signaling Pathways That Regulate the Crustacean Molting Gland

Abstract

A pair of Y-organs (YOs) are the molting glands of decapod crustaceans. They synthesize and secrete steroid molting hormones (ecdysteroids) and their activity is controlled by external and internal signals. The YO transitions through four physiological states over the molt cycle, which are mediated by molt-inhibiting hormone (MIH; basal state), mechanistic Target of Rapamycin Complex 1 (mTORC1; activated state), Transforming Growth Factor-β (TGFβ)/Activin (committed state), and ecdysteroid (repressed state) signaling pathways. MIH, produced in the eyestalk X-organ/sinus gland complex, inhibits the synthesis of ecdysteroids. A model for MIH signaling is organized into a cAMP/Ca2+-dependent triggering phase and a nitric oxide/cGMP-dependent summation phase, which maintains the YO in the basal state during intermolt. A reduction in MIH release triggers YO activation, which requires mTORC1-dependent protein synthesis, followed by mTORC1-dependent gene expression. TGFβ/Activin signaling is required for YO commitment in mid-premolt. The YO transcriptome has 878 unique contigs assigned to 23 KEGG signaling pathways, 478 of which are differentially expressed over the molt cycle. Ninety-nine contigs encode G protein-coupled receptors (GPCRs), 65 of which bind a variety of neuropeptides and biogenic amines. Among these are putative receptors for MIH/crustacean hyperglycemic hormone neuropeptides, corazonin, relaxin, serotonin, octopamine, dopamine, allatostatins, Bursicon, ecdysis-triggering hormone (ETH), CCHamide, FMRFamide, and proctolin. Contigs encoding receptor tyrosine kinase insulin-like receptor, epidermal growth factor (EGF) receptor, and fibroblast growth factor (FGF) receptor and ligands EGF and FGF suggest that the YO is positively regulated by insulin-like peptides and growth factors. Future research should focus on the interactions of signaling pathways that integrate physiological status with environmental cues for molt control.

Comparative Genomic and Transcriptomic Analyses of CHHs and Their Putative Receptors in Scylla paramamosain, Portunus trituberculatus, and Eriocheir sinensis

“…Of which, our hepatopancreatic CHHR-like clade was consistent with the CHHR2 clade, and four putative CHHRs (Sv_GPCR_A12, Gl_GPCRA12, Pc-GPCRA52, and Pc-GPCRA63) in the CHHR2 clade also expressed in hepatopancreas (Veenstra, 2015;Buckley et al, 2016;Tran et al, 2019). In the review, only four CHHRs in the CHHR1 clade (review, Mykles, 2021), our analysis expanded this clade, which three subgroups were separated from each other. Moreover, three putative CHHRs constitute a new CHHR set.…”

“…Expressions of Sp-GPCR-A33, Sp-GPCR-A35 and their orthologs in various tissues suggests pleiotropic functions, and it should be determined whether they were activated by the multi-tissue expressed CHH1-v2/CHH2 or by the pleiotropic CHH1-v1. Previous review revealed that decapod putative CHHRs were clustered into two clades (CHHR1 and CHHR2) (review, Mykles, 2021). In this study, more decapod putative CHHR sequences were collected to construct phylogenetic tree to clarify their clustering.…”

“…The eyestalk ganglia, also referred to as the X-organ-sinus gland (XO-SG) complex is composed of medulla terminalis X-organs (XO), which is involved in the synthesis of neuropeptides, aggregation of XO terminals, sinus gland (SG), as well as in neuropeptide storage and release (reviews, Fingerman, 1997;Webster et al, 2012). Crustacean hyperglycemic hormone superfamily neuropeptides (CHHs) are classic XO-SG complex neuropeptides that are involved in reproduction (reviews, Chung et al, 2010;Jayasankar et al, 2020), molting (reviews, Chung et al, 2010;Webster, 2015a;Chen et al, 2020;Mykles and Chang, 2020;Mykles, 2021), metabolism (reviews, Chung et al, 2010;Chen et al, 2020), immunity (reviews, Chen et al, 2020;Tong et al, 2021), stress (reviews, Chen et al, 2020;Tong et al, 2021), and osmotic regulation (reviews, Chung et al, 2010;Webster, 2015b;Chen et al, 2020).…”

Evaluation of Krill Meal in Commercial Diets for Juvenile Swimming Crab (Portunus trituberculatus)

“…The mTORC1 reacts with insulin and insulin-like peptides (ILPs) via the PI3K pathway, and AKT could be phosphorylated by PI3K through activating phosphoinositidedependent kinase-1; then, mTORC1 could be activated by AKT through phosphorylating tuberous sclerosis complex 2/ PRAS40 [55]. Previous studies have indicated that continuous ecdysis steroid synthesis and secretion in ecdysis glands of insects and crustaceans depend on mTOR protein synthesis [56,57]. The main rate-limiting step of protein synthesis is regulated by the mTOR signaling pathway; mTORC1 directly phosphorylates downstream target proteins ribosomal protein S6 kinase1 (S6K1) and eukaryotic initiation…”

Interaction analysis of hemolymph extracellular vesicles miRNA and hemocytes mRNA reveals genes and pathways associated with molting in Scylla paramamosain

“…Other hormones, such as insulin and juvenile hormone, are also involved in the molting process (Song and Zhou, 2020;Yuan et al, 2020). Crustacean eyestalks are considered to constitute the molt control center and contain the X-organ/sinus gland (XO/SG) complex, which releases a number of peptide hormones such as moltinhibiting hormone and crustacean hyperglycemic hormone into the hemolymph (Mykles, 2021). The hepatopancreas plays a vital role in energy storage and breakdown, nutrient accumulation, and carbohydrate and lipid metabolism during molt (Xu et al, 2020).…”