Hemolymph and transcriptome analysis to understand innate immune responses to hypoxia in Pacific abalone.

Hypoxia was thought to inhibit immune responses, causing severe mortality to marine organisms. The Pacific abalone, Haliotis discus hannai, is the most widely cultured abalone species in China, but suffering from "summer mortality" in which hypoxia has been one of the main reasons. The effect of hypoxia exposure on immune responses in H. discus hannai was investigated, including cellular immune response using flow cytometry and transcriptome profiles. The influence of hypoxia treatment on the total hemocyte count (THC) of H. discus hannai was rather limited but the hemocyte survival rate of abalone increased during 48 h exposure. There was an initial rise in the production of phagocytes and reactive oxygen species (ROS) shortly (3 h) after hypoxic stimulation, but finally decreased after 48 h. This indicates that hypoxia inhibited redox activity of abalone. RNA-seq studies of gill tissues also revealed immune response mechanism in abalone after 24 h of hypoxia. Totally 954 differentially expressed genes (DEGs) were detected under different degrees of deoxygenation. Though oxidation-reduction turbulence was a result of both up- and down-regulated DEGs, cell death/apoptosis induction resulted from up-regulated DEGs, whilst DNA metabolic and immunity suppression resulted from down-regulated DEGs. In summary, our data provides evidence that deoxygenation greatly affects abalone immunity, probably making it more vulnerable. The present study also lays the foundation for further research in hypoxia-associated conditions in abalone aquaculture.

Identification and characteristics of muscle growth-related microRNA in the Pacific abalone, Haliotis discus hannai.

BACKGROUND: The Pacific abalone, Haliotis discus hannai, is the most important cultivated abalone in China. Improving abalone muscle growth and increasing the rate of growth are important genetic improvement programs in this industry. MicroRNAs are important small noncoding RNA molecules that regulate post-transcription gene expression. However, no miRNAs have been reported to regulate muscle growth in H. discus hannai. RESULTS: we profiled six small RNA libraries for three large abalone individuals (L_HD group) and three small individuals (S_HD group) using RNA sequencing technology. A total of 205 miRNAs, including 200 novel and 5 known miRNAs, were identified. In the L_HD group, 3 miRNAs were up-regulated and 7 were down-regulated compared to the S_HD specimens. Bioinformatics analysis of miRNA target genes revealed that miRNAs participated in the regulation of cellular metabolic processes, the regulation of biological processes, the Wnt signaling pathway, ECM-receptor interaction, and the MAPK signaling pathway, which are associated with regulating growth. Bone morphogenetic protein 7 (BMP7) was verified as a target gene of hdh-miR-1984 by a luciferase reporter assay and we examined the expression pattern in different developmental stages. CONCLUSION: This is the first study to demonstrate that miRNAs are related to the muscle growth of H. discus hannai. This information could be used to study the mechanisms of abalone muscle growth. These DE-miRNAs may be useful as molecular markers for functional genomics and breeding research in abalone and closely related species.