Search

Marine bivalves could accumulate paralytic shellfish toxins (PSTs) produced by toxic microalgae, which might induce oxidative stress. Glutathione peroxidases (GPxs) are key enzymes functioning in the antioxidant defense, whereas our understanding of their roles in PST challenge in bivalves is limited. Herein, through genome-wide screening, we identified nine (CfGPx) and eight (PyGPx) GPx genes in Zhikong scallop (Chlamys farreri) and Yesso scallop (Patinopecten yessoensis), respectively, and revealed the expansion of GPx3 sub-family in both species. RNA-Seq analysis revealed high expression of scallop GPx3s after D stage larva during early development, and in adult hepatopancreas. However, in scallops exposed to PST-producing dinoflagellates, no GPx was significantly induced in the hepatopancreas. In scallop kidneys where PSTs were transformed to higher toxic analogs, most CfGPxs were up-regulated, with CfGPx3s being acutely and chronically induced by Alexandrium minutum and A. catenella exposure, respectively, but only one PyGPx from GPx3 subfamily was up-regulated by A. catenella exposure. Our results suggest the function of scallop GPxs in protecting kidneys against the oxidative stresses by PST accumulation or transformation. The tissue-, species-, and toxin-dependent expression pattern of scallop GPxs also implied their functional diversity in response to toxin exposure. [ABSTRACT FROM AUTHOR]

• Seven PC4s genes (PyPC4s) were identified in Patinopecten yessoensis genome. • Phylogenetic analysis confirmed gene expansion and evolutionary relationship of PyPC4s. • PyPC4s showed functional roles in growth and development of Yesso scallop. • Expression regulations of PyPC4s showed a time-dependent pattern with functional complementation in response to low pH stress. • Our data provide novel clues to inductively functional differentiations of PyPC4s in response to OA. Transcriptional coactivator p15 (PC4), considered a multifunctional chromosome associated protein, is actively involved in transcription regulation, DNA replication, damage repair and chromosome formation. Although studies have reported significant effects of PC4 in most vertebrates and some invertebrates, the complete PC4 gene members are less systematically identified and characterized in scallops. In this study, seven PC4 genes (PyPC4s) were identified in the Yesso scallop Patinopecten yessoensis using whole-genome scanning via bioinformatic analyses. Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of the seven genes. Expression profiles of PyPC4s were further investigated in embryos/larvae at all developmental stages, healthy adult tissues, and mantles that were exposed to low pH stress (pH 6.5 and 7.5) with different time durations (3, 6, 12 and 24 h). Spatiotemporal expression patterns indicated the functional roles of PyPC4s at all development stages and in healthy adult tissues, with PY-3235.33 demonstrating remarkably high constitutive expressions. Expression regulations (up- and down-regulation) of PyPC4s under low pH stress levels demonstrated a time-dependent pattern with functional complementation and/or enhancement, revealing that PyPC4s exhibited differentiated functions in response to ocean acidification (OA). Collectively, our data offer a novel perspective stating that low pH is a potential inducer leading to functional differentiation of PyPC4s in scallops. The results provide preliminary information on the versatile roles of PC4(s) in bivalves in response to OA. [ABSTRACT FROM AUTHOR]

As filter-feeding animals mainly ingesting microalgae, bivalves could accumulate paralytic shellfish toxins (PSTs) produced by harmful algae through diet. To protect themselves from the toxic effects of PSTs, especially the concomitant oxidative damage, the production of superoxide dismutase (SOD), which is the only eukaryotic metalloenzyme capable of detoxifying superoxide, may assist with toxin tolerance in bivalves. To better understand this process, in the present study, we performed the first systematic analysis of SOD genes in bivalve Chlamys farreri , an important aquaculture species in China. A total of six Cu/Zn-SOD s ( SOD1-6 ) and two Mn-SOD s ( SOD7 , SOD8 ) were identified in C. farreri , with gene expansion being revealed in Cu/Zn-SOD s. In scallops exposed to two different PSTs-producing dinoflagellates, Alexandrium minutum and A. catenella , expression regulation of SOD genes was analyzed in the top ranked toxin-rich organs, the hepatopancreas and the kidney. In hepatopancreas, which mainly accumulates the incoming PSTs, all of the six Cu/Zn-SOD s showed significant alterations after A. minutum exposure, with SOD1 , 2 , 3 , 5 , and 6 being up-regulated, and SOD4 being down-regulated, while no significant change was detected in Mn-SOD s. After A. catenella exposure, up-regulation was observed in SOD2 , 4 , 6 , and 8 , and SOD7 was down-regulated. In the kidney, where PSTs transformation occurs, SOD4 , 5 , 6 , and 8 were up-regulated, and SOD7 was down-regulated in response to A. minutum feeding. After A. catenella exposure, all the Cu/Zn-SOD s except SOD1 were up-regulated, and SOD7 was down-regulated in kidney. Overall, in scallops after ingesting different toxic algae, SOD up-regulation mainly occurred in the expanded Cu/Zn-SOD group, and SOD6 was the only member being up-regulated in both toxic organs, which also showed the highest fold change among all the SOD s, implying the importance of SOD6 in protecting scallops from the stress of PSTs. Our results suggest the diverse function of scallop SOD s in response to the PST-producing algae challenge, and the expansion of Cu/Zn-SOD s might be implicated in the adaptive evolution of scallops or bivalves with respect to antioxidant defense against the ingested toxic algae.