Salinity and alkalinity are among the important factors affecting the distribution, survival, growth and physiology of aquatic animals. Chinese sea bass (Lateolabrax maculatus) is an important aquaculture fish species in China that can widely adapt to diverse salinities from freshwater (FW) to seawater (SW) but moderately adapt to highly alkaline water (AW). In this study, juvenile L. maculatus were exposed to salinity change (SW to FW) and alkalinity stress (FW to AW). Coordinated transcriptomic responses in L. maculatus gills were investigated and based on the weighted gene co-expression network analysis (WGCNA), 8 and 11 stress-responsive modules (SRMs) were identified for salinity change and alkalinity stress, respectively, which revealed a cascade of cellular responses to oxidative and osmotic stress in L. maculatus gills. Specifically, four upregulated SRMs were enriched with induced differentially expressed genes (DEGs) for alkalinity stress, mainly corresponding to the functions of “extracellular matrix” and “anatomical structure”, indicating a strong cellular response to alkaline water. Both “antioxidative activity” and “immune response” functions were enriched in the downregulated alkaline SRMs, which comprised inhibited alkaline specific DEGs, revealing the severely disrupted immune and antioxidative functions under alkalinity stress. These alkaline-specific responses were not revealed in the salinity change groups with only moderately inhibited osmoregulation and induced antioxidative response in L. maculatus gills. Therefore, the results revealed the diverse and correlated regulation of the cellular process and stress response in saline-alkaline water, which may have arisen through the functional divergence and adaptive recruitment of the co-expression genes and will provide vital insights for the development of L. maculatus cultivation in alkaline water.

Filter-feeding bivalves can accumulate paralytic shellfish toxins (PST) produced by toxic microalgae, which may induce oxidative stress and lipid peroxidation. Peroxisomal acyl-coenzyme A oxidases (ACOXs) are key enzymes functioning in maintaining redox and lipid homeostasis, but their roles in PST response in bivalves are less understood. Herein, a total of six and six ACOXs were identified in the Chlamys farreri and Patinopecten yessoensis genome, respectively, and the expansion of ACOX1s was observed. Gene expression analysis revealed an organ/tissue-specific expression pattern in both scallops, with all ACOXs being predominantly expressed in the two most toxic organs, digestive glands and kidneys. The regulation patterns of scallop ACOXs after exposure to different PST-producing algaes Alexandrium catenella (ACDH) and A. minutum (AM-1) were revealed. After ACDH exposure, more differentially expressed genes (DEGs) were identified in C. farreri digestive glands (three) and kidneys (five) than that in P. yessoensis (two), but the up-regulated DEGs showed similar expression patterns in both species. In C. farreri, three DEGs were found in both digestive glands and kidneys after AM-1 exposure, with two same CfACOX1s being acutely and chronically induced, respectively. Notably, these two CfACOX1s also showed different expression patterns in kidneys between ACDH (acute response) and AM-1 (chronic response) exposure. Moreover, inductive expression of CfACOXs after AM-1 exposure was observed in gills and mantles, and all DEGs in both tissues were up-regulated and their common DEGs exhibited both acute and chronic induction. These results indicate the involvement of scallop ACOXs in PST response, and their plasticity expression patterns between scallop species, among tissues, and between the exposure of different PST analogs.

The cysteine aspartic acid-specific protease (caspase) family is distributed across vertebrates and invertebrates, and its members are involved in apoptosis and response to cellular stress. The Zhikong scallop (Chlamys farreri) is a bivalve mollusc that is well adapted to complex marine environments, yet the diversity of caspase homologues and their expression patterns in the Zhikong scallop remain largely unknown. Here, we identified 30 caspase homologues in the genome of the Zhikong scallop and analysed their expression dynamics during all developmental stages and following exposure to paralytic shellfish toxins (PSTs). The 30 caspase homologues were classified as initiators (caspases-2/9 and caspases-8/10) or executioners (caspases-3/6/7 and caspases-3/6/7-like) and displayed increased copy numbers compared to those in vertebrates. Almost all of the caspase-2/9 genes were highly expressed throughout all developmental stages from zygote to juvenile, and their expression in the digestive gland and kidney was slightly influenced by PSTs. The caspase-8/10 genes were highly expressed in the digestive gland and kidney, while PSTs inhibited their expression in these two organs. After exposure to different Alexandrium PST-producing algae (AM-1 and ACDH), the number of significantly up-regulated caspase homologues in the digestive gland increased with the toxicity level of PST derivatives, which might be due to the higher toxicity of GTXs produced by AM-1 compared to the N-sulphocarbamoyl analogues produced by ACDH. However, the effect of these two PST-producing algae strains on caspase expression in the kidney seemed to be stronger, possibly because the PST derivatives were transformed into highly toxic compounds in scallop kidney, and suggested an organ-dependent response to PSTs. These results indicate the dedicated control of caspase gene expression and highlight their contribution to PSTs in C. farreri. This work provides a further understanding of the role of caspase homologues in the Zhikong scallop and can guide future studies focussing on the role of caspases and their interactions with PSTs.

Bivalve molluscs are filter-feeding organisms that can accumulate paralytic shellfish toxins (PST) through ingesting toxic marine dinoflagellates. While the effects of PST accumulation upon the physiology of bivalves have been documented, the underlying molecular mechanism remains poorly understood. In this study, transcriptomic analysis was performed in the gills of Zhikong scallop (Chlamys farreri) after 1, 3, 5, 10, and 15 day(s) exposure of PST-producing dinoflagellate Alexandrium minutum. Higher numbers of differentially expressed genes (DEGs) were detected at day 1 (1538) and day 15 (989) than that at day 3 (77), day 5 (82), and day 10 (80) after exposure, and most of the DEGs were only regulated at day 1 or day 15, highlighting different response mechanisms of scallop to PST-producing dinoflagellate at different stages of exposure. Functional enrichment results suggested that PST exposure induced the alterations of nervous system development processes and the activation of xenobiotic metabolism and substance transport processes at the acute and chronic stages of exposure, respectively, while the immune functions were inhibited by PST and might ultimately cause the activation of apoptosis. Furthermore, a weighted gene co-expression network was constructed, and ten responsive modules for toxic algae exposure were identified, among which the yellow module was found to be significantly correlated with PST content. Most of the hub genes in the yellow module were annotated as solute carriers (SLCs) with eight being OCTN1s, implying their dominant roles in regulating PST accumulation in scallop gills. Overall, our results reveal the gene set responding to and involved in PST accumulation in scallop gills, which will deepen our understanding of the molecular mechanism of bivalve resistance to PST.

Bovine endometritis is a prevalent uterine disease that directly curtails reproductive performance and indirectly reduces milk production by increasing cal