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

Crustacean hyperglycemic hormone superfamily neuropeptides (CHHs) are typical crustacean eyestalk hormones that include the crustacean hyperglycemic hormone (CHH), moult-inhibiting hormone (MIH), vitellogenesis/gonad-inhibiting hormone (VIH/GIH) and mandibular organ-inhibiting hormone (MOIH), which are divided into two subfamilies: type I CHH (included CHH) and type II CHH (consisting of MIH, VIH/GIH, and MOIH). They are involved in various biological activities, such as metabolism, molting, reproduction, and osmotic regulation. Discovery of the ion transport peptide (ITP) in insects expanded the members of CHHs and revealed that CHHs are not restricted to crustaceans. In this study, we focused on three economically important crabs: the mud crab, Scylla paramamosain, the swimming crab, Portunus trituberculatus, and the Chinese mitten crab, Eriocheir sinensis. Their genomes, Pacbio full-length transcriptomic data as well as comparative RNA-seq data were obtained and used to analyze the genomic structures and expression patterns of CHHs and their putative receptors through bioinformatic methods. Two type I CHH members (CHH1 and CHH2) were identified, of which CHH1 had two splice variants, CHH1-v1 and CHH1-v2. One copy of type II CHH (MIH) was found in P. trituberculatus and E. sinensis. While most decapods, including S. paramamosain, have two copies of type II CHHs (MIH/VIH), these MIH/VIHs are adjacent to each other on the same chromosome. Besides type I and II CHH, ITP-like peptides have also been found in the three crabs, and they are mainly expressed in the eyestalk. Four, five, and three G protein-coupled receptors (GPCRs) were identified in S. paramamosain, P. trituberculatus, and E. sinensis, respectively, which might be putative CHH receptors. These GPCRs were divided into three groups. One group was composed of two contiguous genomic position GPCRs, and they were mainly expressed in the hepatopancreas. These findings provide a basis for further studies on CHHs receptor binding tests and on CHHs/GPCRs signaling pathways.

Effects of crustacean hyperglycemic hormone (CHH) RNA interference on regulation of glucose metabolism in Litopenaeus vannamei after ammonia-N exposure

To unveil the adaptation of Litopenaeus vannamei to elevated ambient ammonia-N, crustacean hyperglycemic hormone (CHH) was knocked down to investigate its function in glucose metabolism pathway under ammonia-N exposure. When CHH was silenced, haemolymph glucose increased significantly during 3-6 h, decreased significantly during 12-48 h, and recovered to the control groups’ level at 72 h. After CHH knockdown, DA contents reduced significantly during 3-24 h, which recovered after 48 h. Besides, the expressions of GC and DA1R in the hepatopancreas decreased significantly, while DA4R increased significantly. Correspondingly, the contents of cAMP, cGMP and DAG and the expressions of PKA, PKG, AMPKα and AMPKγ were significantly downregulated, while the levels of PKC and AMPKβ were significantly upregulated. The expressions of CREB and GLUT2 decreased significantly, while GLUT1 increased significantly. Moreover, glycogen content, glycogen synthase and glycogen phosphorylase activities in hepatopancreas and muscle were significantly increased. Furthermore, the levels of key enzymes HK, PK and PFK in glycolysis, rate-limiting enzymes CS in TCA, and critical enzymes PEPCK, FBP and G6P in gluconeogenesis were significantly decreased in hepatopancreas. These results suggest that CHH affects DA, and then they affect their receptors respectively to transmit glucose metabolism signals into the hepatopancreas of L. vannamei under ammonia-N stress. CHH acts on cGMP-PKG-AMPKα-CREB pathway through GC, and CHH affects DA to influence cAMP-PKA-AMPKγ-CREB and DAG-PKC-AMPKβ-CREB pathways, thereby regulating GLUTs, inhibiting glycogen metabolism and promoting glycolysis and gluconeogenesis. This study contributes to further understand glucose metabolism mechanism of crustacean in response to environmental stress.