Sex bias miRNAs in Cynoglossus semilaevis could play a role in transgenerational inheritance

Circulating MicroRNAs Indicative of Sex and Stress in the European Seabass (Dicentrarchus labrax): Toward the Identification of New Biomarkers

MicroRNAs (miRNAs) constitute a new category of biomarkers. Studies on miRNAs in non-mammalian species have drastically increased in the last few years. Here, we explored the use of miRNAs as potential, poorly invasive markers, to identify sex and characterize acute stress in fish. The European seabass (Dicentrarchus labrax) was chosen as a model because of its rapid response to stress and its specific sex determination system, devoid of sexual chromosomes. We performed a small RNA-sequencing analysis in the blood plasma of male and female European seabass (mature and immature) as well as in the blood plasma of juveniles submitted to an acute stress and sampled throughout the recovery period (at 0 h, 0.5 h, 1.5 h and 6 h). In immature individuals, both miR-1388-3p and miR-7132a-5p were up-regulated in females, while miR-499a-5p was more abundant in males. However, no miRNAs were found to be differentially expressed between sexes in the blood plasma of mature individuals. For the acute stress analysis, five miRNAs (miR-155-5p, miR-200a-3p, miR-205-1-5p, miR-143-3p, and miR-223-3p) followed cortisol production over time. All miRNAs identified were tested and validated by RT-qPCR on sequenced samples. A complementary analysis on the 3'UTR sequences of the European seabass allowed to predict potential mRNA targets, some of them being particularly relevant regarding stress regulation, e.g., the glucocorticoid receptor 1 and the mineralocorticoid receptor. The present study provides new avenues and recommendations on the use of miRNAs as biomarkers of sex or stress of the European seabass, with potential application on other fish species.

Comparative piRNAs Profiles Give a Clue to Transgenerational Inheritance of Sex-Biased piRNAs in Cynoglossus semilaevis

Piwi interacting RNAs (piRNAs) are involved in the epigenetic and post-transcriptional gene silencing of retrotransposons in germ line cells, especially in spermatogenesis. There are many related reports on model organisms, such as flies and mice. In fish, however, there are few studies on piRNAs. Cynoglossus semilaevis, a benthic warm water flatfish, with remarkable sexual dimorphism, especially the "pseudo males" with sex reversal, mating with normal females to produce viable offspring, is an ideal material for the study of sex development. Here, sperm piwi-interacting RNAs profiles of Cynoglossus semilaevis were characterized, comparing between male and pseudomale groups. Differential piRNAs were identified with their predicted and annotated targets. Attention was then focused on candidate piRNAs associated with sex development and methylation. We continued to compare the expression levels of 10 candidates differentially expressed piRNAs in F1 spermatozoa. Quantitative RT-PCR demonstrated that five of the ten piRNAs showed sex bias consistent with parental sequencing results, with four significantly higher expression level in sperm of five males offspring than that of pseudomales, while one piRNAs showed the opposite expression profile. The five signature piRNAs (piR-mmu-49600337, piR-mmu-95849, piR-xtr-7474223, piR-xtr-1790334, and piR-mmu-4491546) could be employed as male-specific molecular biomarkers for C. semilaevis. Besides, this study also implied the possibility of transgenerational inheritance of sex-biased piRNAs exiting in sperm of Cynoglossus semilaevis.