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

Identification of sex-biased MiRNA markers informative of heat-past events

Elevated temperatures during early developmental stages play a pivotal role in the fate of the adult sexual phenotype of fish populations, usually leading to male-skewed sex ratios. This is the case with European sea bass (Dicentrarchus labrax), one of the most important species in the European aquaculture industry. To unveil informative markers of the past thermal events, we investigated changes in the miRNome within the gonads of this species. Consequently, we exposed European sea bass to elevated temperatures (21ºC) during early development (from 7 to 68 days post fertilization). After one-year post-heat treatment growing at natural temperature, a miRNA-sequencing analysis was conducted in the ovaries and testes of juvenile fish. The examination of miRNA expression levels identified three and twelve miRNAs in ovaries and testes, respectively, reflecting past thermal events. To assess the evolutionary conservation of these identified miRNAs in gonads, we cross-referenced our data with miRNome public information from ovaries and testes in nine additional fish species from the FishmiRNA database. This analysis uncovered 33 potential sex-biased markers present in at least five studied species along the evolutionary timeline. For instance, miR-155, miR-429, and miR-140 were consistently female-skewed, while miR-143, miR-499, and miR-135b-3p were consistently male-skewed. In addition, among these markers, three conserved sex-skewed miRNAs proved to be informative regarding past thermal events in the ovaries (e.g., miR-192-5p, miR-146a-5p and miR-143-3p) and four in the testes (miR-129-5p, miR-724-5p, miR-143-3p, and miR-223-3p). Notably, miR-223-3p was conserved female-skewed, but showed upregulation in males exposed to high temperature, and miR-143-3p was inhibited in both heated females and males. These miRNAs could serve as markers of heat-induced masculinization. This research broadens the inventory of sex-specific miRNAs across evolution in fish, and elucidates thermosensitive miRNAs in the gonads.

Circulating miRNAs involved in the immune response of the European seabass (Dicentrarchus labrax)

Understanding the immune response in fish through transcriptomic and microRNA (miRNA) profiling may unlock critical insights into disease resistance mechanisms. The objective of the present study was to examine the immune modulation of the European seabass (Dicentrarchus labrax) following bacterial infection and vaccination. Therefore, sequencing of circulating miRNA isolated from blood serum and 3'UTR transcriptome sequencing of head kidney was conducted. In the infected fish 19 miRNAs were found to be differentially expressed. This included two novel miRNAs exhibiting high levels in the infected fish. Regarding circulating miRNAs following vaccination, three specific miRNAs have been identified that demonstrated a substantial increase in expression. Two of them, miR-216b and miR-30a-5p, have been documented to possess the capacity to delay the progression of viral infections. 3'UTR sequencing analysis of the infected fish revealed no significant enrichment of down-regulated transcripts. However, there was a significant enrichment of up-regulated transcripts related to ribosome biogenesis and protein processing. In vaccinated fish up-regulated transcripts did not demonstrate substantial enrichment. Down-regulated genes on the other hand were involved in cytoskeleton organization and apoptosis, indicating that cellular disruption might be a potential hindrance to effective immunity. Overall, these results provide first insights into the progression and regulation of host immune responses to pathogen infection and vaccination. Moreover, the detection of in total 13 differential expressed circulating miRNAs, including regulators of critical innate immunity-related genes such as Toll-like receptor 18, suggests a potential for circulating miRNAs to play a significant role in the post-transcriptional control of fish immune defenses.

Chronic Adolescent Restraint Stress Downregulates miRNA-200a Expression in Male and Female C57BL/6J and BALB/cJ Mice

Adolescence is a critical developmental period when the brain is plastic, and stress exposure can have lasting physiological consequences. One mechanism through which adolescent stress may have lasting effects is by altering microRNAs (miRNAs), leading to wide-scale gene expression changes. Three prior independent studies used unbiased approaches (RNA sequencing or microarray) to identify miRNAs differentially expressed by chronic variable stress in male rodents. In all three studies, miRNA-200a was differentially expressed in areas of the brain associated with emotion regulation. The current study extends this research to determine if chronic non-variable adolescent stress downregulates miRNA-200a expression by looking at two strains (BALB/cJ and C57BL/6J) of male and female mice. We utilized a 14-day (2 h/day) restraint stress protocol and verified stress effects on adolescent body weight gain and circulating corticosterone concentrations relative to non-restraint controls. Mice were then left undisturbed until they were euthanized in adulthood, at which time brains were collected to measure miRNA-200a in the ventral hippocampus. Three weeks after adolescent stress ended, differences in body weight between groups were no longer significant; however, animals exposed to stress had less miRNA-200a expression in the ventral hippocampus than control animals. These data implicate miRNA-200a expression as a potential mechanism by which adolescent stress can have persistent impacts on multiple outcomes in both male and female mice.

Plasma cortisol and production of miRNAs in red drum (Sciaenops ocellatus) exposed to three distinct challenges

The red drum Sciaenops ocellatus is a marine fish species of high commercial interest. Despite improvements in current aquaculture practices, there are still concerns about the impact of daily manipulations regarding fish welfare. To investigate how does fish respond to various challenges, S. ocellatus juveniles were submitted to two acute challenges, namely a confinement stress and a cold-temperature shock, as well as a chronic stress challenge consisting of 18 days of repetitive challenge events. The level of cortisol produced by individuals was used as a measure of activation hypothalamic-pituitary-interrenal (HPI) axis. A significant increase in cortisol levels was detected only after the confinement stress. Interestingly, the fish exposed to a chronic stress for 18 days exhibited cortisol levels significantly lower than those of non-challenged fish. The small RNA-sequencing conducted for the chronic stress experiment only allowed us to identify two plasmatic microRNAs more abundant in non-challenged fish (miR-205-1-5p and let-7b-5p) compared to challenged fish. The miR-205-1-5p was of particular interest since it was already detected in previous studies on other fish species. In silico analysis allowed to predict potentially highly conserved mRNA targets of this specific miRNA, among which is tnfrsfa that plays a key role in the secondary stress response.