Comparative Biochemistry and Physiology A-Molecular & Integrative Physiology最新文献

Heat shock proteins (HSPs) are well known to prevent and repair protein damage caused by various abiotic stressors, but their role in low temperature and freezing stress is not well-characterized in insects compared to other thermal challenges such as heat stress. Ice formation in and around cells is hypothesized to cause protein damage, yet many species of insects can survive freezing, suggesting HSPs may be an important mechanism in freeze tolerance. Here, we studied HSP70 in a freeze-tolerant cricket Gryllus veletis to better understand the role of HSPs in this phenomenon. We measured expression of one heat-inducible HSP70 isoform at the mRNA level (using RT-qPCR), as well as the relative abundance of total HSP70 protein (using semi-quantitative Western blotting), in five tissues from crickets exposed to a survivable heat treatment (2 h at 40 °C), a 6-week fall-like acclimation that induces freeze tolerance, and a survivable freezing treatment (1.5 h at -8 °C). While HSP70 expression was upregulated by heat at the mRNA or protein level in all tissues studied (fat body, Malphigian tubules, midgut, femur muscle, nervous system ganglia), no tissue exhibited HSP70 upregulation within 2-24 h following a survivable freezing stress. During fall-like acclimation to mild low temperatures, we only saw moderate upregulation of HSP70 at the protein level in muscle, and at the RNA level in fat body and nervous tissue. Although HSP70 is important for responding to a wide range of stressors, our work suggests that this chaperone may be less critical in the preparation for, and response to, moderate freezing stress.

Studies using the embryos of the freshwater prawn Macrobrachium olfersii have reported changes in embryonic cells after exposure to ultraviolet B (UVB) radiation, such as DNA damage and apoptosis activation. Considering the importance of mitochondria in embryonic cells, this study aimed to characterize the aspects of mitochondrial morphofunctionality in M. olfersii embryos and mitochondrial responses to UVB radiation exposure. The coding sequences of genes Tfam, Nrf1, Mfn1, and Drp1 were identified from the transcriptome of M. olfersii embryos. The phylogenetic relationship showed strong amino acid identity and a highly conserved nature of the sequences. Additionally, the number of mitochondrial DNA (mtDNA) copies were higher in the early embryonic days. The results showed that the expression of the analyzed genes was highly regulated during embryonic development, increasing their levels near hatching. Furthermore, when embryos were exposed to UVB radiation, mitochondrial biogenesis was activated, recognized by higher levels of transcripts of genes Tfam and Nrf1, accompanied by mitochondrial fission. Additionally, these mitochondrial events were supported by an increase of mtDNA copies. Our results showed that UVB radiation was able to change the mitochondrial morphofunctionality, and under the current knowledge, certainly compromise embryonic cellular integrity. Additionally, mitochondria is an important cellular target of this radiation and its responses can be used to assess environmental stress caused by UVB radiation in embryos of aquatic species.

Central neurons of the common goldfish (Carassius auratus) are exceptional in their capacity to survive Ca²⁺-induced excitotoxicity and cell death during hypoxia. Horizontal cells (HCs) are inhibitory interneurons of the retina that are tonically depolarized by the neurotransmitter, glutamate, yet preserve intracellular Ca²⁺ homeostasis. In HCs isolated from goldfish, and in the absence of glutamatergic input, intracellular Ca²⁺ concentration ([Ca²⁺]_i) is protected from prolonged exposure to hypoxia by mitochondrial ATP-dependent K⁺ (mK_ATP) channel activity. In the present study, we investigated the effects of hypoxia upon [Ca²⁺]_i in isolated HCs during tonic activation by glutamate to better predict the effects of hypoxia in the active retina. Dynamic changes in [Ca²⁺]_i were measured using the ratiometric Ca²⁺ indicator, Fura-2. Application of 100 μM glutamate during hypoxia (P_O2 = 25 mmHg) produced a 1.3-fold greater rise in [Ca²⁺]_i compared to the same glutamate stimulus during normoxia. The hypoxia-dependent increase in [Ca²⁺]_i was abolished by application of 5-hydroxydecanoic acid, which renders mK_ATP channels inactive. Extracellular Ca²⁺ did not contribute to the elevated [Ca²⁺]_i observed during hypoxia, as the effect persisted in Ca²⁺-free solution and during application of verapamil, an L-type Ca²⁺ channel blocker. By contrast, inhibition of the mitochondrial Ca²⁺ uniporter or ryanodine receptors (with ruthenium red or ryanodine, respectively) abolished the hypoxia-dependent rise in [Ca²⁺]_i. This study reports an mK_ATP-dependent rise in [Ca²⁺]_i during hypoxia in HCs activated by glutamate, and suggests roles for the mitochondria and intracellular Ca²⁺ stores in regulating this mechanism.

Infertility in hyperprolactinemic females is attributed to the dysregulation of GnRH release, subsequently affecting gonadotropin levels, and ultimately leading to anovulation. However, in addition to the hypothalamus, prolactin receptor (PRLR) is expressed in ovaries as well, suggesting potential local effects of PRL in cases of hyperprolactinemia. We have developed an experimental model of sulpiride (SPD)-induced hyperprolactinemia using a wild rodent, the plains vizcacha, and studied the implications of pharmacological PRL levels on folliculogenesis and steroid production. Ovaries of SPD females showed a striking number of atretic follicles along with a reduction in the collective number of viable follicles leading to a higher atretic/viable follicle ratio compared to that of control females (CTL) (P < 0.05). In terms of sensitivity to the hormonal environment, SPD ovaries substantially changed their potential responsiveness to pituitary PRL, as evidenced by the three-fold increase in PRLR expression alongside heightened expression of both gonadotropic receptors in comparison to CTL ovaries (P < 0.05). Circulating estradiol (E2) values doubled post-treatment in the SPD females, which also showed higher expressions of aromatase and 17β-hydroxysteroid dehydrogenase, along with both E2 receptors, ERα and ERβ than the CTL group (P < 0.05). Our findings strongly suggest that hyperprolactinemia-dependent dysregulation of ovarian function can be explained at least partially, by PRL direct actions facilitated by the heightened expression of PRLR in follicles and corpora lutea. Possibly these PRL actions synergize with those triggered by gonadotropic hormones ultimately leading to alteration of the steroidogenic pathway, folliculogenesis disruption and increased atresia.

Understanding contraction dynamics of skeletal muscle is critically important to appreciate performance capabilities of skeletal structures, especially for structures responsible for feeding and/or locomotion. Furthermore, it is important to understand how temperature can impact contraction dynamics in vertebrates that are regularly exposed to fluctuations in temperature. We aimed to address differences between jaw opening (sternhyoideus), jaw closing (adductor mandibulae) and locomotor (abductor superficialis) muscle contraction dynamics in a labrid fish. Additionally, we aimed to understand how temperature changes impact contraction kinetics in these muscles. To address these aims we collected cunner (Tautogolabrus adspersus) from Long Island Sound and removed their primary locomotor and jaw opening/closing muscles. Following dissection, the muscles were placed on a muscle ergometer that controlled length, stimulus duration and stimulation intensity. Muscles were exposed to 7, 15 and 22 °C for all experiments. We found that the swimming muscle was slower to contract and relax than both feeding muscles. Swimming muscle produced more power than feeding muscles when tested at 8 Hz and 15 °C. Jaw closing muscle produced more force than the other two muscle types when tested at22 °C. Despite these differences, muscle contraction kinetics were remarkably similar across the three muscle types and temperatures. To our knowledge this is the first study to measure in vitro contraction dynamics of fish jaw opening and closing muscle. This advances the understanding of the physiological capabilities of these muscles. Additionally, differences in contraction dynamics can further our understanding of the physiological limits temperature impart on whole muscle contraction.

Early life telomere length is thought to influence and predict an individual's fitness. It has been shown to vary significantly in early life compared to adulthood. Investigating the factors influencing telomere length in young individuals is therefore of particular interest, especially as the relative importance of heredity compared to post-natal conditions remains largely uncertain. Adélie penguins are eco-indicators of the Antarctic ecosystem and their population are currently undergoing variable trajectories due to climate change. Here, we conducted a correlative study to investigate how telomere length was influenced by external and internal factors in Adélie penguin chicks. We found that most of the parameters we tested, including sex, body mass, brood size and hatching order as well as parental foraging trip duration, did not significantly influence chick telomere length at 32 days. However, siblings had similar telomere length, suggesting that hereditary factors play a stronger role in determining telomere length at this stage compared to the post-natal environment. In addition, telomere length and oxidative damage did not directly correlate but did interact in a complex way mediated by chick mass. High levels of oxidative damage were associated with longer telomeres in heavy chicks, whereas they were associated with shorter telomeres in light chicks. Although this mass-dependent relationship between telomere length and oxidative damage needs to be confirmed in future studies, it could reflect two different scenarios: (1) short telomeres may mimic the cost of poor nutritional conditions and oxidative damage in light chicks; (2) long telomeres may be maintained despite high oxidative damage in heavy chicks thanks to optimal nutritional conditions.

Fish are ectothermic animals with temperature playing a key role in their health, growth and survival. Greater occurrence of heat waves and temperature extremes, as a result of global climate change, has the potential to impact both wild and farmed populations. Within aquaculture, production is threatened by a multitude of stressors, including adverse temperatures. The propensity for environmental temperature during early embryo development to influence later life transcriptomic responses has been observed in numerous animal species, and, if harnessed, could provide a method for inducing phenotypic changes in adult aquaculture species. We hypothesise that exposure of rainbow trout embryos to temperature stress results in alterations to transcriptional responsiveness upon re-exposure later in life. To test this hypothesis, we exposed embryos to a range of different heat shock treatments during early development and then analysed their response to thermal stress at five days post hatch (dph), in comparison to naïve fish that experienced no early development heat shock. Hsp70a and hsp70b transcription was measured (using RT-QPCR) as a biomarker for thermal stress response. Significantly greater transcriptional induction of hsp70a in response to post-hatch thermal stress was found in heat shocked larvae compared to naïve larvae (p = 0.0085). The timing, intensity and duration of the initial heat shock was not found to statistically influence the alteration of hsp induction when compared to that of naïve larvae. Together, these results support our hypothesis that heat shock during early development has the potential to affect responsiveness to the same stressor later in life. Future studies should focus on understanding whether this could be utilised to increase robustness of fish in aquaculture.

Climate change will increase the frequency and severity of temperature extremes. Links between host thermal physiology and their gut microbiota suggest that organisms' responses to future climates may be mediated by their microbiomes, raising the question of how the thermal environment influences the microbiome itself. Vertebrate gut microbiomes influence the physiological plasticity of their hosts via effects on immunity, metabolism, and nutrient uptake. The gut microbiota of ectothermic vertebrates in particular are responsive to long-term, sub-lethal gradual increases in environmental temperature. Whether and how the gut microbiota respond to brief exposure to temperatures at the upper limit of host physiological tolerance (CT_max) is poorly understood but could have downstream effects on host fitness. We assayed the CT_max of wood frogs (Lithobates sylvaticus) from 15 populations across a 10° latitudinal gradient. We then characterized the gut microbiota of juveniles at two time points following exposure to CT_max. Frogs from higher latitudes had lower thermal tolerance (lower CT_max) than those from lower latitudes. Unexpectedly, exposure to upper survivable temperature had little to no detectable effect on the frogs' microbiota richness, stability, or composition. Instead, we found a strong effect of time in which frogs kept in recovery conditions for four days had less diverse, but more stable gut microbiota than those that had recovered for only one day, regardless of CT_max exposure. We conclude that while wood frogs from higher latitudes have reduced thermal tolerances than those from lower latitudes, their microbial communities are largely unaffected by brief exposure to high temperatures at the edge of their physiological limits.

In a previous study, we demonstrated successful regeneration of Atlantic salmon gill tissue following up to 50 % filament resection. The present study explored 1) the capacity of gill tissue to regenerate following more severe trauma, 2) if regeneration potential varies across regions of the arch, and 3) how tissue loss impacts the physiology of neighboring unresected filaments. Fish were divided between two resected groups and a control non-resected one. In resection group-1, fish underwent 50 % and 75 % resection in the ventral and medial-dorsal regions of the first arch, while in resection group-2, the location of resection levels were reversed. The degree of filament regeneration and physiology of unresected filaments were measured at 4, 12 and 20 weeks-post-resection (WPR). Overall, the degree of regeneration was significantly higher in 50 % resected filaments relative to 75 % resected filaments. The degree of regeneration did not differ significantly between the resected groups for either of resection levels, suggesting negligible impacts of filament location on arch on regeneration. The concentration of oxidized glutathione (GSSG), total glutathione (GSH), and citrate synthase activity (CSA) in intact filaments were comparable between resected and control fish at both 4 and 20 WPR. However, GSH concentration varied among resected fish with those exhibited higher GSH in intact filaments showed lower regeneration of 50 % resected filaments at 20 WPR. Our results indicate that gill tissue loss exceeding 50 % may significantly impair regeneration and that this level of tissue loss is not associated with a compensatory response (e.g. GSSG, GSH, CSA) of neighboring gill tissue.

Although a giant Egyptian domestic non-migratory duck breed is phenotypically identical to the migratory Mallard, yet it is three times larger. The current study sought to determine the genetic and metabolic differences between this duck and Mallard, which arrives in Egypt in September for wintering and departs in March. Mitochondrial DNA control region (D-loop) was extracted, amplified, sequenced, and analyzed in both ducks. Both ducks were given a high-fat diet (HFD) for 6 weeks to assess their metabolic response to this diet. Polymorphism results indicated that the D-loop is highly variable and both populations expansion is balanced. The hierarchical analysis of molecular variants (AMOVA) and interpopulation difference parameters revealed significant genetic differentiation and minimal gene flow between migrant and resident populations. Phylogeny and Network analyses revealed that domestic ducks are a distinct group that separated from mallards. Physiologically, domestic duck blood and adipose tissue had a higher level of triglycerides and adipocyte volume than that of the depleting arriving migratory Mallard ducks, while leaving Mallard parameters were the highest, suggesting a high level of preparatory fat deposition and utilization before starting the trip. In response to HFD, the expression of FA uptake genes cd36, fabp1 was upregulated similarly in livers of domestic and migratory Mallard ducks, while the expression of lipid accumulation genes dgat2 and plin2 was higher in domestic than in migratory Mallards. However, the highest body mass and adipocytes volume gain was observed in the arriving migratory Mallards. In pectoral muscle, the expression of cd36 and fabp3 was higher in domestic than in leaving ducks, while in arriving Mallards, both genes were not upregulated in response to HFD. Dgat2 was upregulated only in domestic muscle, while lipid oxidation genes cpt1, lpl, and the controlling ppara were more upregulated in leaving Mallard. In conclusion, both ducks can be genetically and metabolically differentiated. Migratory mallards are more flexible and efficient in lipid metabolism than domestic ducks.