IAPs Gene Expansion in the Scallop Patinopecten yessoensis and Their Expression Profiles After Exposure to the Toxic Dinoflagellate.

Inhibitors of apoptosis proteins (IAPs) are conserved regulators involved in cell cycle, cell migration, cell death, immunity and inflammation, should be due to the fact that they can assist with the ability to cope with different kinds of extrinsic or intrinsic stresses. Bivalve molluscs are well adapted to highly complex marine environments. As free-living filter feeders that may take toxic dinoflagellates as food, bivalves can accumulate and put up with significant levels of paralytic shellfish toxins (PSTs). PSTs absorption and accumulation could have a deleterious effect on bivalves, causing negative impact on their feeding and digestion capabilities. In the present study, we analyzed IAP genes (PyIAPs) in Yesso scallop (Patinopecten yessoensis), a major fishery and aquaculture species in China. Forty-seven PyIAPs from five sub-families were identified, and almost half of the PyIAP genes were localized in clusters on two chromosomes. Several sites under positive selection was revealed in the significantly expanded sub-families BIRC4 and BIRC5. After exposure to PST-producing dinoflagellates, Alexandrium catenella, fourteen PyIAPs showed significant responses in hepatopancreas and kidney, and more than eighty-five percent of them were from the expanded sub-families BIRC4 and BIRC5. The regulation pattern of PyIAPs was similar between the two tissues, with more than half exhibited expression suppression within three days after exposure. In contrast to hepatopancreas, more acute changes of PyIAPs expression could be detected in kidney, suggesting the possible involvement of these PyIAPs in tissue-specific PST tolerance. These findings also imply the adaptive expansion of bivalve IAP genes in response to algae derived biotoxins.

Publisher Correction: Evolutionary transcriptomics of metazoan biphasic life cycle supports a single intercalation origin of metazoan larvae.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Evolutionary transcriptomics of metazoan biphasic life cycle supports a single intercalation origin of metazoan larvae.

The transient larva-bearing biphasic life cycle is the hallmark of many metazoan phyla, but how metazoan larvae originated remains a major enigma in animal evolution. There are two hypotheses for larval origin. The 'larva-first' hypothesis suggests that the first metazoans were similar to extant larvae, with later evolution of the adult-added biphasic life cycle; the 'adult-first' hypothesis suggests that the first metazoans were adult forms, with the biphasic life cycle arising later via larval intercalation. Here, we investigate the evolutionary origin of primary larvae by conducting ontogenetic transcriptome profiling for Mollusca-the largest marine phylum characterized by a trochophore larval stage and highly variable adult forms. We reveal that trochophore larvae exhibit rapid transcriptome evolution with extraordinary incorporation of novel genes (potentially contributing to adult shell evolution), and that cell signalling/communication genes (for example, caveolin and innexin) are probably crucial for larval evolution. Transcriptome age analysis of eight metazoan species reveals the wide presence of young larval transcriptomes in both trochozoans and other major metazoan lineages, therefore arguing against the prevailing larva-first hypothesis. Our findings support an adult-first evolutionary scenario with a single metazoan larval intercalation, and suggest that the first appearance of proto-larva probably occurred after the divergence of direct-developing Ctenophora from a metazoan ancestor.

Integration of Biochemical, Cellular, and Genetic Indicators for Understanding the Aging Process in a Bivalve Mollusk Chlamys farreri.

The major causal factors for the irreversible decline in physical vitality during organismal aging are postulated to be a chronic state of cellular redox imbalance, metabolic toxicity, and impaired energy homeostasis. We assessed whether the relevant enzyme activity, oxidative stress, and intracellular ATP might be causally involved in the aging of short-lived Chlamys farreri (life span 4~5 years). A total of eight related biochemical and cellular indicators were chosen for the subsequent analysis. All the indicators were measured in seven different tissues from scallops aged one to four years, and our data support that the aging of C. farreri is associated with attenuated tissue enzyme activity as well as a decreased metabolic rate. Through principal component analysis, we developed an integrated vigor index for each tissue for comprehensive age-related fitness evaluation. Remarkably, all tissue-integrated vigor indexes significantly declined with age, and the kidney was observed to be the most representative tissue. Further transcriptional profiling of the enzymatic genes provided additional detail on the molecular responses that may underlie the corresponding biochemical results. Moreover, these critical molecular responses may be attributed to the conserved hierarchical regulators, e.g., FOXO, AMPKs, mTOR, and IGF1R, which were identified as potentially novel markers for chronic fitness decline with age in bivalves. The present study provides a systematic approach that could potentially benefit the global assessment of the aging process in C. farreri and provide detailed evaluation of the biochemical, cellular, and genetic indicators that might be involved. This information may assist in a better understanding of bivalve adaptability and life span.

Genome-wide identification and expression profiling of the Wnt gene family in three bivalve molluscs.

Cellular signaling initiated by various secreted, cysteine-rich Wnt proteins plays essential roles in regulating animal development and cell stemness. By virtue of its functional diversity and importance, the Wnt gene family has received substantial research interests in a variety of animal species, from invertebrates to vertebrates. However, for bivalve molluscs, one of the ancient bilaterian groups with high morphological diversity, systematic identification and analysis of the Wnt gene family remain lacking. To shed some light on the evolutionary dynamics of this gene family and obtain a more comprehensive understanding, we analyzed the characteristics of the Wnt gene family in three bivalve molluscs, with both genome and extensive transcriptomic resources. Investigation of genomic signatures, functional domains as well as phylogenetic relationships was conducted, and 12, 11, 12 subfamilies were identified in Yesso scallop, Zhikong scallop and Pacific oyster respectively. Spatiotemporal expression profiling suggested that, some bivalve Wnts might coordinate and participate in adult organ/tissue morphogenesis and homeostasis as well as early embryonic development. The transcriptional regulation of oyster Wnt genes showed dynamic and responsive patterns under different environmental stresses, indicating that Wnts may play a role in coping with challenging intertidal environments in bivalves. To our best knowledge, this study presents the first genome-wide study of Wnt gene family in bivalves, and our findings would assist in better understanding of Wnt function and evolution in bivalve molluscs.