Localization and identification of crustacean hyperglycemic hormone producing neurosecretory cells in the eyestalk of blue swimmer crab, Portunus pelagicus

Immunocytochemical Localization of Enzymes Involved in Dopamine, Serotonin, and Acetylcholine Synthesis in the Optic Neuropils and Neuroendocrine System of Eyestalks of Paralithodes camtschaticus

Identifying the neurotransmitters secreted by specific neurons in crustacean eyestalks is crucial to understanding their physiological roles. Here, we combined immunocytochemistry with confocal microscopy and identified the neurotransmitters dopamine (DA), serotonin (5-HT), and acetylcholine (ACh) in the optic neuropils and X-organ sinus gland (XO-SG) complex of the eyestalks of Paralithodes camtschaticus (red king crab). The distribution of Ach neurons was studied by choline acetyltransferase (ChAT) immunohistochemistry and compared with that of DA neurons examined in the same or adjacent sections by tyrosine hydroxylase (TH) immunohistochemistry. We detected 5-HT, TH, and ChAT in columnar, amacrine, and tangential neurons in the optic neuropils and established the presence of immunoreactive fibers and neurons in the terminal medulla in the XO region of the lateral protocerebrum. Additionally, we detected ChAT and 5-HT in the endogenous cells of the SG of P. camtschaticus for the first time. Furthermore, localization of 5-HT- and ChAT-positive cells in the SG indicated that these neurotransmitters locally modulate the secretion of neurohormones that are synthesized in the XO. These findings establish the presence of several neurotransmitters in the XO-SG complex of P. camtschaticus.

Suppression of a Novel Vitellogenesis-Inhibiting Hormone Significantly Increases Ovarian Vitellogenesis in the Black Tiger Shrimp, Penaeus monodon

In this study, a novel Crustacean Hyperglycemic Hormone-type II gene (CHH-type II) was identified and biologically characterized in a shrimp, Penaeus monodon. Based on its structure and function, this gene was named P. monodon vitellogenesis-inhibiting hormone (PemVIH). The complete cDNA sequence of PemVIH consisted of 1,022 nt with an open reading frame (ORF) of 339 nt encoding a polypeptide of 112 amino acids. It was classified as a member of the CHH-type II family based on conserved cysteine residues, a characteristically positioned glycine residue, and the absence of CHH precursor-related peptide (CPRP) domain. The deduced mature PemVIH shared the highest sequence similarities with giant river prawn sinus gland peptide A. Unlike P. monodon gonad-inhibiting hormone (PemGIH), PemVIH was expressed only in the brain and ventral nerve cord, but not the eyestalks. Whole mount immunofluorescence using a newly generated PemVIH antiserum detected positive signals in neuronal cluster 9/11 and 17 of the brain, commissural ganglion (CoG), and neuronal clusters of ventral nerve cord. The presence of PemVIH-positive neurons in CoG, a part of stomatogastric nervous system, suggested a potential mechanism for crosstalk between nutritional and reproductive signaling. The role of PemVIH in vitellogenesis was evaluated using RNA interference technique. Temporal knockdown of PemVIH in female subadults resulted in a 3-fold increase in ovarian vitellogenin expression, suggesting an inhibitory role of PemVIH in vitellogenesis. This study provided novel insight into the control of vitellogenesis and additional strategies for improving ovarian maturation in P. monodon without the current harmful practice of eyestalk ablation.