Xiaoshang Ru

Differential Expression of miRNAs in the Respiratory Tree of the Sea Cucumber Apostichopus japonicus Under Hypoxia Stress

The sea cucumber, an important economic species, has encountered high mortality since 2013 in northern China because of seasonal environmental stress such as hypoxia, high temperature, and low salinity. MicroRNAs (miRNAs) are important in regulating gene expression in marine organisms in response to environmental change. In this study, high-throughput sequencing was used to investigate alterations in miRNA expression in the sea cucumber under different levels of dissolved oxygen (DO). Nine small RNA libraries were constructed from the sea cucumber respiratory trees. A total of 26 differentially expressed miRNAs, including 12 upregulated and 14 downregulated miRNAs, were observed in severe hypoxia (DO 2 mg/L) compared with mild hypoxia (DO 4 mg/L) and normoxic conditions (DO 8 mg/L). Twelve differentially expressed miRNAs were clustered in severe hypoxia. In addition, real-time PCR revealed that 14 randomly selected differentially expressed miRNAs showed significantly increased expressions in severe hypoxia and the expressions of nine miRNAs, including key miRNAs such as Aja-miR-1, Aja-miR-2008, and Aja-miR-184, were consistent with the sequencing results. Moreover, gene ontology and pathway analyses of putative target genes suggest that these miRNAs are important in redox, transport, transcription, and hydrolysis under hypoxia stress. Notably, novel-miR-1, novel-miR-2, and novel-miR-3 were specifically clustered and upregulated in severe hypoxia, which may provide new insights into novel “hypoxamiR” identification. These results will provide a basis for future studies of miRNA regulation and molecular adaptive mechanisms in sea cucumbers under hypoxia stress.

Impact of hypoxia stress on the physiological responses of sea cucumber Apostichopus japonicus: respiration, digestion, immunity and oxidative damage

Hypoxia is one of the most frequently occurring stressors confronted by industrial cultures of sea cucumber and can cause large economic losses and resource degradation. However, its responsive mechanisms are still lacking. In this paper, the physiological responses of Apostichopus japonicus to oxygen deficiency was illustrated, including induced oxidative response and immune defense and changed digestive enzymes activities. Significantly increased activities of alpha-amylase (AMS), acid phosphatase (ACP), lactate dehydrogenase, catalase, peroxidase, succinate dehydrogenase and higher content of malondialdehyde, and decreased activities of lipase and trypsin (TRY) were observed after hypoxia exposure (dissolved oxygen [DO] 2 mg/L). Expressions of key genes showed that AMS, peptidase, ACP, alkaline phosphatase, lysozyme, heat shock protein 70 and glutathione peroxidase were increased and TRY was decreased under hypoxia. With the decline of the DO level, the decreased tendency of oxygen consumption rates was different in varied weight groups. Moreover, respiratory trees were observed degraded under long-term hypoxia stress, thus leading a negative effect of respiration. These results could help to develop a better understanding of the responsive mechanism of sea cucumber under hypoxia stress and provide a theoretical basis for the prevention of hypoxia risk.

Effect of desiccation in shade on in vitro oocyte maturation and development of the sea cucumber Apostichopus japonicus (Echinodermata: Holothuroidea)

Abstract Techniques for in vitro oocyte maturation are important for studying maturation regulatory mechanisms, cell differentiation, and embryonic development. In this study, after Apostichopus japonicus gonads were dissected, oocytes, together with gonadal fluid extracted from gonads, were dried in shade. The effects of three temperatures (17, 21, and 25 °C) on oocyte maturation and following development were studied. The results showed that germinal vesicle breakdown (GVBD) of most oocytes occurred after desiccation, and those oocytes with GVBD could be fertilized and develop normally. There were no significant differences in the percentages of GVBD and individuals in blastula and gastrula stages between 17 and 21 °C (p > .05). The percentages of GVBD reached a maximum (17 °C: 98.6%, 21 °C: 97.1%) after 2 h of desiccation. The percentages of blastulae and gastrulae reached the maximum of more than 80% after 2.5–3.5 h of desiccation. At 25 °C, the percentages of GVBD, blastulae, and gastrulae reached a maximum of 76.7, 61.0, and 59.9% after 3.5 h of desiccation, respectively, and were significantly lower than that at 17 and 21 °C (p < .01). This study not only provided an effective and simple technique for in vitro induction of A. japonicus oocyte maturation, but also furthered understanding of gamete biology of this species.