As a wild resource, the large yellow croaker Larimichthys crocea has been seriously threatened since the mid-1980s. Owing to the implementation of protection measures, such as the establishment of a protection zone, fishing prohibitions, restocking programs and successful mariculture, its resources have gradually recovered year by year. Limited by the low spatial resolution and incomplete spatial coverage of sampling stations, the spatial genetic structure and diversity of large yellow croakers from the southern Yellow Sea and north-central East China Sea remains unclear. In order to evaluate the genetic diversity status of this wild stock, 22 wild sites were collected from the southern Yellow Sea and north-central East China Sea and analyzed by investigating genetic variability and its population structure using mitochondrial COI sequence in this study. Among the 662 sequences, a total of 71 different haplotypes were defined. The haplotype diversity (h) and nucleotide diversity (π) values were 0.644~1.000 and 0.00220~0.00473 respectively. The highest h and π occurred in the southern Yellow Sea (YS). AMOVA analysis showed no genetic differentiation among those 22 sites after Bonferroni correction. By comparing with previous studies, the croaker has maintained relatively steady genetic diversity in recent years. Our result also suggested that the croakers in the South Yellow Sea and north-central East China Sea belonged to the same group. Thus, they can be released as a management unit without regard for heterogenicity among those in the sea area. The YS populations can serve as parents for released fish fries in the South Yellow Sea and north-central East China Sea.

The mud crab, Scylla paramamosain, has abundant nutrients in the ovary, where numerous lipids accumulate during ovarian maturation. However, the mechanism behind the accumulation of lipids in the ovary of mud crab during ovarian maturation is largely unknown. This study conducted a comparative transcriptome analysis of the ovaries of mud crabs at various stages of ovarian maturation. A total of 63.69 Gb of clean data was obtained, with a Q30 of 93.34%, and 81,893 unigenes were identified, including 10,996 differentially expressed genes (DEGs). After KEGG enrichment of these DEGs, MAPK signaling pathway was significantly enriched during vitellogenesis. Moreover, the expression levels of genes involved in carbohydrate, amino acid, and lipid metabolism were found to be higher during vitellogenesis. The two genes (Sp-Eip75B and Sp-Eip78C) that are homologous to the vertebrate gene PPARγ in the PPAR signaling pathway, were identified. Additionally, genes in MAPK signaling pathway might regulate lipid metabolism through PPAR signaling pathway based on Protein-Protein Interaction (PPI) network. These findings suggest that MAPK signaling pathway plays a critical role in lipid metabolism in the ovary during vitellogenesis, which provides new insights into the mechanism of lipid accumulation during ovarian maturation in mud crabs.

3‐Hydroxy‐3‐methylglutaryl coenzyme‐A (HMG‐CoA) reductases (HMGRs), which catalyze the conversion of HMG‐CoA to mevalonate, may have an important role in the synthesis of methyl farnesoate (MF). In this study, we obtained two HMGR cDNA sequences termed Sp‐HMGR1 (membrane‐bound form) and Sp‐HMGR2 (soluble form), which encode 967 and 654 amino acids, respectively. The two cDNAs possess entirely identical sequences except that Sp‐HMGR1 is 1,382 bp, which encodes a sterol‐sensed domain (SSD; a membrane‐bound domain) and was first found in crustacean HMGR, larger than Sp‐HMGR2. Thus, it was deduced that these cDNAs might be derived from a single genomic DNA sequence. Sp‐HMGRs have the typical features of the HMGR class of proteins. However, residue 844 in Sp‐HMGR1, which is usually occupied by a Ser residue in other species, has an unusual Ala substitution. This Ser is thought to be involved in enzyme activity regulation by reversible phosphorylation. A putative “PEST” sequence that, until now, has only been found in crustacean species was also identified in the C‐terminus of both transcripts, and a sterol‐sensing domain, which was first found in crustacean species, was identified in Sp‐HMGR1; these findings suggest that Sp‐HMGR might function in some special regulatory mechanism. Furthermore, the quantitative real‐time polymerase chain reaction results showed that the two transcripts have different expression patterns; Sp‐HMGR2 was mainly expressed in the mandibular organ (MO) of adult crabs, whereas Sp‐HMGR1 was mainly expressed in other tissues and fertilized eggs up until the fourth juvenile crab stage. The fluctuating gene expression seemed to suggest a relationship between Sp‐HMGRs and the development of the crab, especially during the larval stage. Besides, the fluctuation of Sp‐HMGR1 in ovary, brain, and thoracic ganglia during the ovary development seemed to have some correlation with the nutrition accumulation of ovaries, whether the SSD domain evolved in this process deserve further investigation. Moreover, it remains unclear whether the significant variation in ovary, brain, and thoracic ganglia during ovary development suggests that other tissues in addition to the MO could synthesize MF. © 2015 IUBMB Life, 67(12):954–965, 2015

The sesquiterpenoid hormone methyl farnesoate (MF) plays a vital role during crustacean development, which is mainly evidenced by its varied titers during different developmental stages. However, the biosynthesis pathways of MF remain obscure to some extent. In this study, we identified the complete MF biosynthesis and related pathway genes in Scylla paramamosain, including three involved in acetyl-CoA metabolism, eight in the mevalonate pathway, five in the sesquiterpenoids synthesis pathway, and five in the methionine cycle pathway. Bioinformatics, genomic structure, and phylogenetic analysis indicated that the JH biosynthesis genes might have experienced evolution after species differentiation. The mRNA tissue distribution analysis revealed that almost all genes involving in or relating to MF syntheses were highly expressed in the mandibular organ (MO), among which juvenile hormone acid methyltransferase was exclusively expressed in the MO, suggesting that most of these genes might mainly function in MF biosynthesis and that the methionine cycle pathway genes might play a crucial regulatory role during MF synthesis. In addition, the phylogenetic and tissue distribution analysis of the cytochrome P450 CYP15-like gene suggested that the epoxidized JHs might exist in crustaceans, but are mainly synthesized in hepatopancreas rather than the MO. Finally, we also found that betaine-homocysteine S-methyltransferase genes were lost in insects while methionine synthase was probably lost in most insects except Folsomia candida, indicating a regulatory discrepancy in the methionine cycle between crustaceans and insects. This study might increase our understanding of synthetic metabolism tailored for sesquiterpenoid hormones in S. paramamosain and other closely related species.

Variability in food availability leads to condition-dependent investments in reproduction. This study is aimed at understanding the metabolic response and regulatory mechanism of female Scylla paramamosain in response to starvation in a temporal- and tissue-specific manner. The mud crabs were starved for 7 (control), 14, 28, and 40 days for histological and biochemical analysis in the hepatopancreas, ovary, and serum, as well as for RNA sequencing on the hepatopancreas and ovary. We further highlighted candidate gene modules highly linked to physiological traits. Collectively, our observations suggested that starvation triggered endogenous ovarian maturation at the expense of hepatopancreas mass, with both metabolic adjustments to optimize energy and fatty acid supply from hepatopancreas to ovary in the early phase, followed by the activation of autophagy-related pathways in both organs over prolonged starvation. These specific adaptive responses might be considered efficient strategies to stimulate ovarian maturation of Scylla paramamosain under fasting stress, which improves the nutritional value of female mud crabs and other economically important crustaceans.