Hypoxia-induced epigenetic transgenerational miRNAs dysregulation involved in reproductive impairment of ovary.

Hypoxia is a potent endocrine disruptor that is posing serious problems to the fish reproductive systems. Our previous studies reported that hypoxia could cause a transgenerational impairment of ovarian development and interfere hatching success in F2 offspring of marine medaka fish (Oryzias melastigma) through epigenetic regulation. As part of the epigenetic regulation, we investigated the involvement of microRNAs (miRNAs) in hypoxia-induced transgenerational reproductive impairments. In the present study, we used comparative small RNA sequencing to reveal that hypoxia caused miRNA dysregulation in ovaries of F0 hypoxia group and F2 transgenerational group. We found 4 common dysregulated miRNA in the F0 and F2 generations. Furthermore, integrated miRNA-mRNA analysis, followed by gene ontology enrichment analysis on the hypoxia-dysregulated miRNA-target genes further highlighted the importance of these dysregulated miRNAs in biological processes related to reproduction. More importantly, we identified 3 miRNA-mRNA pairs (novel miRNA-525-DIAPH2, novel miRNA-525-MYOCD, and novel miRNA-525-RAI14) that might play epigenetic roles in hypoxia-induced reproductive impairment. For the first time, our findings suggested the involvement of miRNA in hypoxia-induced reproductive impairments may be inherited via a transgenerational manner.

Characterisation of the metallothionein gene in the Sydney rock oyster and its expression upon metal exposure in oysters with different prior metal exposure histories.

The metal-binding protein metallothionein (MT) is widely used as a biomarker of metal contamination. In this study, we cloned a MT gene (sgMT) from the Sydney rock oyster Saccostrea glomerata. The gene encodes a MT-I protein with a classical αß domain structure and is expressed as two transcripts resulting from alternative polyadenylation. The gene promoter contains two putative metal-responsive elements (MREs) which are known to be required for metal-inducible transcription. A specific and efficient qPCR assay was developed to quantify sgMT mRNA expression. Further, we assessed whether prior metal exposure history influences sgMT mRNA expression upon subsequent metal exposure. Oysters with varying prior metal exposure histories (contaminated and reference) were exposed to Cu, Cd and Zn. Expression of sgMT generally increased with metal dose, and oysters with an elevated past metal exposure history exhibited higher sgMT expression under Cd and Zn stress, representing a potential acclimatory response to prior metal exposure.