Sex differences in early transcriptomic responses to oxidative stress in the copepod Tigriopus californicus

The role of mitochondria in sex- and age-specific gene expression in a species without sex chromosomes

Mitochondria perform an array of functions, many of which involve interactions with gene products encoded by the nucleus. These mitochondrial functions, particularly those involving energy production, can be expected to differ between sexes and across ages. Here, we measured mitochondrial effects on sex- and age-specific gene expression in parental and reciprocal F1 hybrids between allopatric populations of Tigriopus californicus with over 20% mitochondrial DNA divergence. Because the species lacks sex chromosomes, sex-biased mitochondrial effects are not confounded by the effects of sex chromosomes. Results revealed pervasive sex differences in mitochondrial effects, including effects on energetics and aging involving nuclear interactions throughout the genome. Using single-individual RNA sequencing, sex differences were found to explain more than 80% of the variance in gene expression. Males had higher expression of mitochondrial genes and mitochondrially targeted proteins (MTPs) involved in oxidative phosphorylation (OXPHOS), while females had elevated expression of non-OXPHOS MTPs, indicating strongly sex-dimorphic energy metabolism at the whole organism level. Comparison of reciprocal F1 hybrids allowed insights into the nature of mito-nuclear interactions, showing both mitochondrial effects on nuclear expression, and nuclear effects on mitochondrial expression. While based on a small set of crosses, sex-specific increases in mitochondrial expression with age were associated with longer life. Network analyses identified nuclear components of strong mito-nuclear interactions and found them to be sexually dimorphic. These results highlight the profound impact of mitochondria and mito-nuclear interactions on sex- and age-specific gene expression.

Early-Life Exposure to Paraquat Aggravates Sex-Specific and Progressive Abnormal Non-Motor Neurobehavior in Aged Mice

Early-life exposure to environmental neurotoxicants is known to have lasting effects on organisms. In this study, we aim to investigate the impacts of PQ exposure during early developmental stages and adult re-challenge in aged mice on non-motor neurobehavior. Two mouse models, which were exposed once during early life stage and re-exposure at adulthood, were created to explore the long-term effects of PQ on non-motor neurobehavior. As the results showed, early-life exposure to PQ caused impairment in working memory and cognitive ability in aged male mice, but not in female mice, exhibiting a sex-specific impairment. Moreover, male mice that were re-challenged with PQ at adulthood following early-life exposure also exhibited non-motor neurobehavioral disorders. Notably, re-exposure to PQ exacerbated neurobehavioral disorders and anxiety levels compared to single exposure during different life stages. Collectively, early-life exposure to PQ can result in irreversible impairments in non-motor neurobehavior and increase susceptibility to subsequent insults in male mice, but not in female mice, suggesting greater sensitivity in male rodents to PQ-induced non-motor neurobehavioral deficits.

Decoupled responses of the copepod Eurytemora affinis transcriptome and its microbiota to dissolved copper exposure

Chemical contamination is a common threat to biota thriving in estuarine and coastal ecosystems. Of particular importance is that trace metals tend to accumulate and exert deleterious effects on small invertebrates such as zooplankton, which are essential trophic links between phytoplankton and higher-level consumers in aquatic food webs. Beyond the direct effects of the contamination, we hypothesized that metal exposure could also affect the zooplankton microbiota, which in turn might further impair host fitness. To assess this assumption, copepods (Eurytemora affinis) were sampled in the oligo-mesohaline zone of the Seine estuary and exposed to dissolved copper (25 µg.L^-1) over a 72-hour time period. The copepod response to copper treatment was assessed by determining transcriptomic changes in E. affinis and the alteration of its microbiota. Unexpectedly, very few genes were differentially expressed in the copper-treated copepods compared to the controls for both male and female samples, while a clear dichotomy between sex was highlighted with 80% of the genes showing sex-biased expression. In contrast, copper increased the taxonomic diversity of the microbiota and resulted in substantial compositional changes at both the phyla and genus levels. Phylogenetic reconstruction of the microbiota further suggested that copper mitigated the phylogenetic relatedness of taxa at the basal tree structure of the phylogeny, whereas it strengthened it at the terminal branches. Increased terminal phylogenetic clustering in the copper-treated copepods coincided with higher proportions of bacterial genera previously identified as copper resistant (e.g., Pseudomonas, Acinetobacter, Alkanindiges, Colwellia) and a higher relative abundance of the copA_ox gene encoding a periplasmic inducible multi-copper oxidase. The enrichment in micro-organisms likely to perform copper sequestration and/or enzymatic transformation processes, underlines the need to consider the microbial component during evaluation of the vulnerability of zooplankton to metallic stress.

Dephosphorylation of CatC at Ser-18 improves salt and oxidative tolerance via promoting its tetramerization in rice

Catalase (CAT) is a vital antioxidant enzyme, while phosphorylation pivotally regulates its function. Many phosphosites have been identified in CAT, but their functions remained largely elusive. We functionally studied five phosphoserines (Ser-9, -10, -11, -18, and -205) of CatC in rice (Oryza sativa L.). Phospho-Ser-9 and - 11 and dephospho-Ser-18 promoted the enzymatic activity of CatC and enhanced oxidative and salt tolerance in yeast. Phosphorylation status of Ser-18 did not affect CatC peroxisomal targeting and stability, but dephospho-Ser-18 promoted CatC tetramerization to enhance its activity. Moreover, overexpression of dephospho-mimic form CatC^S18A in rice significantly improved the tolerance to salt and oxidative stresses by inhibiting the H₂O₂ accumulation. Together, these results elucidate the mechanism underlying dephosphorylation at Ser-18 promotes CatC activity and salt tolerance in rice. Ser-18 is a promising candidate phosphosite of CatC for breeding highly salt-tolerant rice.

Mitochondrial effects on fertility and longevity in Tigriopus californicus contradict predictions of the mother's curse hypothesis

Strict maternal inheritance of mitochondria favours the evolutionary accumulation of sex-biased fitness effects, as mitochondrial evolution occurs exclusively in female lineages. The 'mother's curse' hypothesis proposes that male-harming mutations should accumulate in mitochondrial genomes when they have neutral or beneficial effects on female fitness. Rigorous empirical tests have largely focused on Drosophila, where support for the predictions of mother's curse has been mixed. We investigated the impact of mother's curse mutations in Tigriopus californicus, a minute crustacean. Using non-recombinant backcrosses, we introgressed four divergent mitochondrial haplotypes into two nuclear backgrounds and recorded measures of fertility and longevity. We found that the phenotypic effects of mitochondrial mutations were context dependent, being influenced by the nuclear background in which they were expressed, as well as the sex of the individual and rearing temperature. Mitochondrial haplotype effects were greater for fertility than longevity, and temperature effects were greater for longevity. However, in opposition to mother's curse expectations, females had higher mitochondrial genetic variance than males for fertility and longevity, little evidence of sexual antagonism favouring females was found, and the impacts of mitonuclear mismatch harmed females but not males. Together, this indicates that selection on mitochondrial variation has not resulted in the accumulation of male mutation load in Tigriopus californicus.

Exogenous oxidative stressors elicit differing age and sex effects in Tigriopus californicus

As organisms age, cellular function declines in a time-dependent manner. Oxidative stress induced by reactive oxygen species damages cellular machinery and contributes to senescence which narrows the homeostatic window needed to maintain function and survive stress. Sex differences in longevity are apparent in many species and may be related to sex-specific homeostatic responses. Here we use the emerging aging model system Tigriopus californicus, the splashpool copepod, to estimate sex- and age-specific tolerances to two chemical oxidants, hydrogen peroxide and paraquat. Sex-specific tolerance was estimated for both oxidants simultaneously for 15 age-classes. As animals aged, hydrogen peroxide tolerance decreased but paraquat tolerance increased. Also, we observed no sex difference for hydrogen peroxide tolerance, while females were more tolerant of paraquat. Our results demonstrate that oxidative stressors can have dramatically different sex and age effects in Tigriopus californicus. These findings underscore the challenges ahead in understanding relationships among oxidative stressors, sex, and aging.

Associations of PM2.5 and road traffic noise with mental health: Evidence from UK Biobank

BACKGROUND

The associations of atmospheric particulate matter with diameters of 2.5 μm or less (PM2.5) and road traffic noise with mental disorders in men and women are not well studied.

OBJECTIVES

We aim to examine the cross-sectional associations of PM2.5 and road traffic noise with mental disorders in men and women.

METHODS

The baseline data of the UK Biobank study (2006-2010) were used. Mental disorders including symptoms of nerves, anxiety, tension or depression (NATD), major depression, and bipolar disorder were assessed by validated questions. Verified models were used to estimate PM2.5 and road traffic noise.

RESULTS

A total of 334,986 participants with measurements of NATD and 90,706 participants with measurements of major depression and bipolar disorder were included in the analysis. After adjusting for covariates, the odds for the risk of NATD symptoms increased by 2.31 (95% CI: 2.15-2.50) times per 10 μg/m³ increase in PM2.5. The odds for the risk of major depression and bipolar disorder increased by 2.26 and 4.99 times per 10 μg/m³ increase in PM2.5. On the other hand, higher road traffic noise exposure was significantly associated with a higher risk of NATD symptoms (Decile 6-8 (54.9-57.8 dB), OR: 1.03, 95% CI: 1.01-1.06; Decile 9-10 (≥57.8 dB), OR: 1.04, 95% CI: 1.01-1.07) and bipolar disorder (Decile 2-5 (52.1-54.9 dB), OR: 1.26, 95% CI: 1.00-1.59; Decile 6-8 (54.9-57.8 dB), OR: 1.30, 95% CI: 1.02-1.65; Decile 9-10 (≥57.8 dB), OR: 1.54, 95% CI: 1.21-1.97). Interestingly, a negative association was observed between moderate road traffic noise and major depression (Decile 2-5 (52.1-54.9 dB), OR: 0.95, 95% CI: 0.90-1.00). Interactions between PM2.5 exposure with age, gender, and sleeplessness for NATD symptoms were observed (P < 0.05), while interactions between road traffic noise exposure with age and gender were observed (P < 0.05).

CONCLUSIONS

We found a positive association between PM2.5 and mental disorders. Meanwhile, we found a positive association of road traffic noise with NATD symptoms and bipolar disorder and a negative association of moderate road traffic noise with major depression. Also, the effect modifications of these associations by age, gender, or sleeplessness may exist.

Mitonuclear interactions alter sex-specific longevity in a species without sex chromosomes

Impaired mitochondrial function can lead to senescence and the ageing phenotype. Theory predicts degenerative ageing phenotypes and mitochondrial pathologies may occur more frequently in males due to the matrilineal inheritance pattern of mitochondrial DNA observed in most eukaryotes. Here, we estimated the sex-specific longevity for parental and reciprocal F1 hybrid crosses for inbred lines derived from two allopatric Tigriopus californicus populations with over 20% mitochondrial DNA divergence. T. californicus lacks sex chromosomes allowing for more direct testing of mitochondrial function in sex-specific ageing. To better understand the ageing mechanism, we estimated two age-related phenotypes (mtDNA content and 8-hydroxy-20-deoxyguanosine (8-OH-dG) DNA damage) at two time points in the lifespan. Sex differences in lifespan depended on the mitochondrial and nuclear backgrounds, including differences between reciprocal F1 crosses which have different mitochondrial haplotypes on a 50 : 50 nuclear background, with nuclear contributions coming from alternative parents. Young females showed the highest mtDNA content which decreased with age, while DNA damage in males increased with age and exceed that of females 56 days after hatching. The adult sex ratio was male-biased and was attributed to complex mitonuclear interactions. Results thus demonstrate that sex differences in ageing depend on mitonuclear interactions in the absence of sex chromosomes.

Evidence for hybrid breakdown in production of red carotenoids in the marine invertebrate Tigriopus californicus

The marine copepod, Tigriopus californicus, produces the red carotenoid pigment astaxanthin from yellow dietary precursors. This ‘bioconversion’ of yellow carotenoids to red is hypothesized to be linked to individual condition, possibly through shared metabolic pathways with mitochondrial oxidative phosphorylation. Experimental inter-population crosses of lab-reared T. californicus typically produces low-fitness hybrids is due in large part to the disruption of coadapted sets nuclear and mitochondrial genes within the parental populations. These hybrid incompatibilities can increase variability in life history traits and energy production among hybrid lines. Here, we tested if production of astaxanthin was compromised in hybrid copepods and if it was linked to mitochondrial metabolism and offspring development. We observed no clear mitonuclear dysfunction in hybrids fed a limited, carotenoid-deficient diet of nutritional yeast. However, when yellow carotenoids were restored to their diet, hybrid lines produced less astaxanthin than parental lines. We observed that lines fed a yeast diet produced less ATP and had slower offspring development compared to lines fed a more complete diet of algae, suggesting the yeast-only diet may have obscured effects of mitonuclear dysfunction. Astaxanthin production was not significantly associated with development among lines fed a yeast diet but was negatively related to development in early generation hybrids fed an algal diet. In lines fed yeast, astaxanthin was negatively related to ATP synthesis, but in lines fed algae, the relationship was reversed. Although the effects of the yeast diet may have obscured evidence of hybrid dysfunction, these results suggest that astaxanthin bioconversion may still be related to mitochondrial performance and reproductive success.

Susceptibility of the Non-Targeted Crustacean Eurytemora affinis to the Endocrine Disruptor Tebufenozide: A Transcriptomic Approach

Copepods are zooplanktonic crustaceans ubiquitously widespread in aquatic systems. Although they are not the target, copepods are exposed to a wide variety of pollutants such as insect growth regulators (IGRs). The aim of this study was to investigate the molecular response of a non-targeted organism, the copepod Eurytemora affinis, to an IGR. Adult males and females were exposed to two sub-lethal concentrations of tebufenozide (TEB). Our results indicate a sex-specific response with a higher sensitivity in males, potentially due to a differential activation of stress response pathways. In both sexes, exposure to TEB triggered similar pathways to those found in targeted species by modulating the transcription of early and late ecdysone responsive genes. Among them were genes involved in cuticle metabolism, muscle contraction, neurotransmission, and gametogenesis, whose mis-regulation could lead to moult, locomotor, and reproductive impairments. Furthermore, genes involved in epigenetic processes were found in both sexes, which highlights the potential impact of exposure to TEB on future generations. This work allows identification of (i) potential biomarkers of ecdysone agonists and (ii) further assessment of putative physiological responses to characterize the effects of TEB at higher biological levels. The present study reinforces the suitability of using E. affinis as an ecotoxicological model.

Glutathione S-Transferases in Marine Copepods

The glutathione S-transferase (GST) is a complex family of phase II detoxification enzymes, known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) to a wide variety of endogenous and exogenous electrophilic compounds for detoxification purposes. In marine environments, copepods are constantly exposed to multiple exogenous stressors, thus their capability of detoxification is key for survival. Full identification of the GST family in copepods has been limited only to few species. As for insects, the GST family includes a wide range of genes that, based on their cellular localization, can be divided in three classes: cytosolic, microsomal, and mitochondrial. The role of GSTs might have class-specific features, thus understanding the nature of the GST family has become crucial. This paper covers information of the GST activity in marine copepods based on studies investigating gene expression, protein content, and enzymatic activity. Using published literature and mining new publicly available transcriptomes, we characterized the multiplicity of the GST family in copepods from different orders and families, highlighting the possible role of these genes as biomarker for ocean health status monitoring.

First De Novo Transcriptome of the Copepod Rhincalanus gigas from Antarctic Waters

Simple Summary

Compared to more accessible sites, organisms inhabiting Antarctic waters have been poorly investigated. This study provides the first molecular resource (transcriptome from whole individual) for the eucalanoid copepod Rhincalanus gigas, one of the predominant zooplankton species of Antarctic waters. Sequence analyses identified possible adaptation strategies adopted by the organism to cope with cold environments. Among those, we identified in R. gigas transcriptome three predicted genes encoding for antifreeze proteins and gene duplication within the glutathione metabolism pathway. This new molecular resource, provided here, will be useful to study the physiology, ecology, and biology of R. gigas and it increases the information available for polar environments.

Abstract

Antarctic waters are the largest almost untapped diversified resource of our planet. Molecular resources for Antarctic organisms are very limited and mostly represented by sequences used for species genotyping. In this study, we present the first transcriptome for the copepod Rhincalanus gigas, one of the predominant zooplankton species of Antarctic waters. This transcriptome represents also the first molecular resource for an eucalanoid copepod. The transcriptome is of high quality and completeness. The presence of three predicted genes encoding antifreeze proteins and gene duplication within the glutathione metabolism pathway are suggested as possible adaptations to cope with this harsh environment. The R. gigas transcriptome represents a powerful new resource for investigating the molecular basis associated with polar biological processes and ecology.