Selection of references for quantitative real-time PCR analysis of microRNAs in Nile tilapia (Oreochromis niloticus) under osmotic stress.

MicroRNAs play crucial regulatory roles in various aspects of development and physiology, including environmental adaptation and stress responses in teleosts. RT-qPCR is the most commonly used method for studying microRNA expression, with the accuracy and reliability of results depending on the use of an appropriate reference gene for normalization. This study aimed to evaluate seven miRNAs (U6, Let-7a, miR-23a, miR-25-3, miR-103, miR-99-5, and miR-455) expression stability in different tissues of Nile tilapia subjected to osmotic stress. Fish were divided into two groups: a control and an experimental group, raised in 0 and 12 ppt salinity water respectively. After 21 days, brain, gills, liver, and posterior intestine were collected for analysis. Different mathematical algorithms (geNorm, NormFinder, BestKeeper, and the comparative ΔCt method) were employed to identify the most suitable reference miRNAs. The results indicate that the miR-455/miR-23a combination is a robust reference for normalizing miRNA expression levels in studies of osmotic stress responses in Nile tilapia. The stability of miRNA expression can vary depending on specific stress conditions and biological processes, underscoring the necessity of selecting appropriate normalizing miRNAs for each experimental context. This study identifies reliable reference genes for future RT-qPCR analyses of miRNA expression, thereby enhancing our understanding of molecular responses in fish to environmental challenges. These insights are fundamental to the development of new technologies for the improved management and sustainability of aquaculture practices.

A Pilot Study of Gene Expression Modulation from Antioxidant System of Killifish Austrolebias charrua After Exposure to Roundup Transorb®.

Roundup Transorb® (RDT) is the most popular glyphosate-based herbicide (GHB) used in agriculture, and its impact extends to non-target organisms. The annual killifish Austrolebias charrua is an endangered species endemic to southern South America and inhabits temporary ponds. This study evaluates the effects of RDT concentrations (0.065 and 5 mg/L GAE) on A. charrua exposed for 96 h. Gene expression of cat, sod2, gstα, gclc, and ucp1 was evaluated on the liver and gills. Highlighting that even at low concentrations permitted by Brazilian legislation, the RDT can have adverse effects on A. charrua.

MicroRNA qPCR normalization in Nile tilapia (Oreochromis niloticus): Effects of acute cold stress on potential reference targets.

The Nile tilapia (Oreochromis niloticus) is one of the most important cultured fish worldwide, but tilapia culture is largely affected by low temperatures. Recent studies suggest that microRNAs (miRNAs) regulate cold tolerance traits in fish. In general, qPCR-based methods are the simplest and most accurate forms of miRNA quantification. However, qPCR data heavily depends on appropriate normalization. Therefore, the aim of the present study is to determine whether the expression of previously tested, stably expressed miRNAs are affected by acute cold stress in Nile tilapia. For this purpose, one small nuclear RNA (U6) and six candidate reference miRNAs (miR-23a, miR-25-3, Let-7a, miR-103, miR-99-5, and miR-455) were evaluated in four tissues (blood, brain, liver, and gills) under two experimental conditions (acute cold stress and control) in O. niloticus. The stability of the expression of each candidate reference miRNA was analyzed by four independent methods (the delta Ct method, geNorm, NormFinder, and BestKeeper). Further, consensual comprehensive ranking of stability was built with RefFinder. Overall, miR-103 was the most stable reference miRNA in this study, and miR-103 and Let-7a were the best combination of reference targets. Equally important, Let-7a, miR-23a, and miR-25-3 remained consistently stable across different tissues and experimental groups. Considering all variables, U6, miR-99-5, and miR-455 were the least stable candidates under acute cold stress. Most important, suitable reference miRNAs were validated in O. niloticus, facilitating further accurate miRNA quantification in this species.

Modulation of miR-429 during osmotic stress in the silverside Odontesthes humensis.

Silverside fish inhabit marine coastal waters, coastal lagoons, and estuarine regions in southern South America. Although silversides are not fully adapted to freshwater, they can tolerate a wide range of salinity variations. MicroRNAs (miRNAs) are a class of ∼22 nucleotide noncoding RNAs, which are crucial regulators of gene expression at post-transcriptional level. Current data indicate that miRNAs biogenesis is altered by situations of environmental stress, thereby altering the expression of target mRNAs. Foremost, the silversides were acutely exposed to 30 g.L-1 of salt to reveal in which tissue miR-429 could be differentially expressed. Thus, fish were acclimated to freshwater (0 g.L-1) and to brackish water (10 g.L-1), and then exposed to opposite salinity treatment. Here, we reveal that miR-429, a gill-enriched miRNA, emerges as a prime osmoregulator in silversides. Taken together, our findings suggest that miR-429 is an endogenous regulator of osmotic stress, which may be developed as a biomarker to assist silverside aquaculture.

Exposure to salinity induces oxidative damage and changes in the expression of genes related to appetite regulation in Nile tilapia (Oreochromis niloticus).

Variations in water salinity and other extrinsic factors have been shown to induce changes in feeding rhythms and growth in fish. However, it is unknown whether appetite-related hormones mediate these changes in Nile tilapia (Oreochromis niloticus), an important species for aquaculture in several countries. This study aimed to evaluate the expression of genes responsible for appetite regulation and genes related to metabolic and physiological changes in tilapia exposed to different salinities. Moreover, the study proposed to sequence and to characterize the cart, cck, and pyy genes, and to quantify their expression in the brain and intestine of the fish by quantitative polymerase chain reaction (qPCR). The animals were exposed to three salinities: 0, 6, and 12 parts per thousand (ppt) of salt for 21 days. Furthermore, lipid peroxidation, reactive oxygen species, DNA damage, and membrane fluidity in blood cells were quantified by flow cytometry. The results indicated an increased expression of cart, pyy, and cck and a decreased expression of npy in the brain, and the same with cck and npy in the intestine of fish treated with 12 ppt. This modulation and other adaptive responses may have contributed to the decrease in weight gain, specific growth rate, and final weight. In addition, we showed oxidative damage in blood cells resulting from increasing salinity. These results provide essential data on O. niloticus when exposed to high salinities that have never been described before and generate knowledge necessary for developing biotechnologies that may help improve the production of economically important farmed fish.

Chronic cold exposure modulates genes related to feeding and immune system in Nile tilapia (Oreochromis niloticus).

Nile tilapia is the fourth most produced species in the global aquiculture panorama. This species requires water temperatures higher than 16 °C to grow and survive, and so, little is known about the effects of low temperatures on genes related to food intake and inflammatory responses. This study brought insights about the modulation of genes in different tissues of Nile tilapia chronically exposed to low temperatures. Thus, sixty animals were divided in two experimental groups: a control group in which the animals remained at the optimum temperature of 24 °C; and an exposed to cold group, in which a decrease in the water temperature was applied until reaching 15 °C. These conditions were maintained for 28 days. Blood samples were collected for flow cytometry analysis, while brain, spleen, liver, and kidney tissues were collected for total RNA extraction, followed by quantitative PCR (RT-qPCR). For genes related to feeding process pathway, it was observed an upregulation in pyy and a downregulation of npy and cart gene expression. Also, pro-inflammatory cytokine genes were modulated in the spleen, kidney and liver with a higher expression of il-1b and tnfα and a reduction in the il-8 and nf-κß gene expressions in the group exposed to 15 °C. The fish exposed to cold presented higher serum cortisol levels than the ones from control group. The blood cell analysis showed a lower level of membrane fluidity and a higher DNA fragmentation and cell disruption in the group exposed to cold. These findings suggest an important effect of a stressful situation in the tilapia organism due to cold exposure. This study brings insights on tilapia wellbeing under low temperature stress. It can be a first step to understanding the appropriate way to cope with cold impacts on aquaculture.

Acute exposition to Roundup Transorb® induces systemic oxidative stress and alterations in the expression of newly sequenced genes in silverside fish (Odontesthes humensis).

Roundup Transorb® (RDT) is a glyphosate-based herbicide commonly used in agricultural practices worldwide. This herbicide exerts negative effects on the aquatic ecosystem and affects bioenergetic and detoxification pathways, oxidative stress, and cell damage in marine organisms. These effects might also occur at the transcriptional level; however, the expression of genes associated with oxidative stress has not been studied well. Odontesthes humensis is a native Brazilian aquatic species naturally distributed in the habitats affected by pesticides, including Roundup Transorb® (RDT). This study evaluated the toxic effects of short-term exposure to RDT on O. humensis. Moreover, the genes related to oxidative stress were sequenced and characterized, and their expressions in the gills, hepatopancreas, kidneys, and brain of the fish were quantified by quantitative reverse transcription-polymerase chain reaction. The animals were exposed to two environmentally relevant concentrations of RDT (2.07 and 3.68 mg L-1) for 24 h. Lipid peroxidation, reactive oxygen species (ROS), DNA damage, and apoptosis in erythrocytes were quantified by flow cytometry. The expression of the target genes was modulated in most tissues in the presence of the highest tested concentration of RDT. In erythrocytes, the levels of lipid peroxidation, ROS, and DNA damage were increased in the presence of both the concentrations of RDT, whereas cell apoptosis was increased in the group exposed to 3.68 mg L-1 RDT. In conclusion, acute exposure to RDT caused oxidative stress in the fish, induced negative effects on cells, and modulated the expression of genes related to the enzymatic antioxidant system in O. humensis.

First Record of Clinostomum sp. (Digenea: Clinostomidae) in Danio rerio (Actinopterygii: Cyprinidae) and the Implication of Using Zebrafish from Pet Stores on Research.

Many scientific studies still use zebrafish from pet stores as animal models, even cutting-edge researches. However, these animals differ genotypically and phenotypically between them. The importance of the use of standardized models is widely recognized. Besides that, another consequence of using zebrafish from unknown origins is the acquisition of parasitized animals. This study aimed to relate the infection by Clinostomum sp. in zebrafish. Animals sold as "high standard" were acquired from a commercial company. Swimming alterations and superficial yellow dots were observed in five zebrafish with clinical signs, which were isolated, euthanized, and necropsied. Muscular yellow cysts with metacercaria associated with lesions were observed. The muscular cysts were responsible for the superficial yellow dots as well as the swimming alterations. The prevalence was 2.5%, and the mean infection intensity was 7 digeneans/host. The cysts measured a mean of 1251.43 µm long × 784.28 µm wide. Metacercariae measured a mean of 4847 µm long × 1353 µm wide. This first report about infection by Clinostomum sp. in zebrafish is globally relevant since the host and the parasite genus currently overlap worldwide. Furthermore, this study sheds light on the importance of the specific pathogen-free commercial creations or laboratory-reared zebrafish for research.

Evaluation of qPCR reference genes in GH-overexpressing transgenic zebrafish (Danio rerio).

Reference genes (RGs) must have a stable expression in tissues in all experimental conditions to normalize real-time quantitative reverse transcription PCR (qRT-PCR) data. F0104 is a highly studied lineage of zebrafish developed to overexpress the growth hormone (GH). It is assumed that the transgenic process may influence the expression levels of commonly used RGs. The objective of the present study was to make a comprehensive analysis of stability of canditade RGs actb1, actb2, b2m, eif2s2, eef1a1, gapdh, rplp2, rpl7, rpl13α, tuba1, and rps18, in gh-transgenic and non-transgenic zebrafish. Liver, brain, intestine and muscle samples from both groups had qRT-PCR results analyzed by dCt, geNorm, NormFinder, BestKeeper, and RefFinder softwares. Consensus analyses among software concluded that rpl13α, rpl7, and eef1a1 are the most stable genes for zebrafish, considering the studied groups and tissues. Gapdh, rps18, and tuba1 suffered variations in stability among different tissues of both groups, and so, they were listed as the genes with lowest stability. Results from an average pairwise variations test indicated that the use of two RGs would generate reliable results for gene expression analysis in the studied tissues. We conclude that genes that are commonly used in mammals for qRT-PCR assays have low stability in both non-transgenic and gh-transgenic zebrafish reinforcing the importance of using species-specific RGs.

Corrigendum: Gene and Blood Analysis Reveal That Transfer from Brackish Water to Freshwater Is More Stressful to the Silverside Odontesthes humensis.

[This corrects the article DOI: 10.3389/fgene.2018.00028.].

Evaluation of Reference Genes to Analyze Gene Expression in Silverside Odontesthes humensis Under Different Environmental Conditions.

Some mammalian reference genes, which are widely used to normalize the qRT-PCR, could not be used for this purpose due to its high expression variation. The normalization with false reference genes leads to misinterpretation of results. The silversides (Odontesthes spp.) has been used as models for evolutionary, osmoregulatory and environmental pollution studies but, up to now, there are no studies about reference genes in any Odontesthes species. Furthermore, many studies on silversides have used reference genes without previous validations. Thus, present study aimed to was to clone and sequence potential reference genes, thereby identifying the best ones in Odontesthes humensis considering different tissues, ages and conditions. For this purpose, animals belonging to three ages (adults, juveniles, and immature) were exposed to control, Roundup®, and seawater treatments for 24 h. Blood samples were subjected to flow-cytometry and other collected tissues to RNA extraction; cDNA synthesis; molecular cloning; DNA sequencing; and qRT-PCR. The candidate genes tested included 18s, actb, ef1a, eif3g, gapdh, h3a, atp1a, and tuba. Gene expression results were analyzed using five algorithms that ranked the candidate genes. The flow-cytometry data showed that the environmental challenges could trigger a systemic response in the treated fish. Even during this systemic physiological disorder, the consensus analysis of gene expression revealed h3a to be the most stable gene expression when only the treatments were considered. On the other hand, tuba was the least stable gene in the control and gapdh was the least stable in both Roundup® and seawater groups. In conclusion, the consensus analyses of different tissues, ages, and treatments groups revealed that h3a is the most stable gene whereas gapdh and tuba are the least stable genes, even being considered two constitutive genes.

Gene and Blood Analysis Reveal That Transfer from Brackish Water to Freshwater Is More Stressful to the Silverside Odontesthes humensis.

Silversides are fish that inhabit marine coastal waters, coastal lagoons, and estuarine regions in southern South America. The freshwater (FW) silversides have the ability to tolerate salinity variations. Odontesthes humensis have similar habitats and biological characteristics of congeneric O. bonariensis, the most studied silverside species and with great economic importance. Studies revealed that O. bonariensis is not fully adapted to FW, despite inhabiting hyposmotic environments in nature. However, there is little information about stressful environments for cultivation of silverside O. humensis. Thus, the aim of this study was to evaluate the stress and osmoregulation responses triggered by the osmotic transfers on silverside O. humensis. Silversides were acclimated to FW (0 ppt) and to brackish water (BW, 10 ppt) and then they were exposed to opposite salinity treatment. Silverside gills and blood were sampled on pre-transfer (D0) and 1, 7, and 15 days (D1, D7, and D15) after changes in environmental salinity, the expression levels of genes atp1a3a, slc12a2b, kcnh1, and hspa1a were determined by quantitative reverse transcription-PCR for evaluation of osmoregulatory and stress responses. Furthermore, glycemia, hematocrit, and osmolality were also evaluated. The expression of atp1a3a was up- and down-regulated at D1 after the FW-BW and BW-FW transfers, respectively. Slc12a2b was up-regulated after FW-BW transfer. Similarly, kcnh1 and hspa1a were up-regulated at D1 after the BW-FW transfer. O. humensis blood osmolality decreased after the exposure to FW. It remained stable after exposure to BW, indicating an efficient hyposmoregulation. The glycemia had a peak at D1 after BW-FW transfer. No changes were observed in hematocrit. The return to the pre-transfer levels at D7 after the significant increases in responses of almost all evaluated molecular and blood parameters indicated that this period is enough for acclimation to the experimental conditions. In conclusion, our results suggest that BW-FW transfer is more stressful to O. humensis than FW-BW transfer and the physiology of O. humensis is only partially adapted to FW.

The Oncopig Cancer Model as a Complementary Tool for Phenotypic Drug Discovery.

The screening of potential therapeutic compounds using phenotypic drug discovery (PDD) is being embraced once again by researchers and pharmaceutical companies as an approach to enhance the development of new effective therapeutics. Before the genomics and molecular biology era and the consecutive emergence of targeted-drug discovery approaches, PDD was the most common platform used for drug discovery. PDD, also known as phenotypic screening, consists of screening potential compounds in either in vitro cellular or in vivo animal models to identify compounds resulting in a desirable phenotypic change. Using this approach, the biological targets of the compounds are not taken into consideration. Suitable animal models are crucial for the continued validation and discovery of new drugs, as compounds displaying promising results in phenotypic in vitro cell-based and in vivo small animal model screenings often fail in clinical trials. Indeed, this is mainly a result of differential anatomy, physiology, metabolism, immunology, and genetics between humans and currently used pre-clinical small animal models. In contrast, pigs are more predictive of therapeutic treatment outcomes in humans than rodents. In addition, pigs provide an ideal platform to study cancer due to their similarities with humans at the anatomical, physiological, metabolic, and genetic levels. Here we provide a mini-review on the reemergence of PDD in drug development, highlighting the potential of porcine cancer models for improving pre-clinical drug discovery and testing. We also present precision medicine based genetically defined swine cancer models developed to date and their potential as biomedical models.

High doses of lipid-core nanocapsules do not affect bovine embryonic development in vitro.

The improvement of in vitro embryo production by culture media supplementation has been a potential tool to increase blastocyst quality and development. Recently, lipid-core nanocapsules (LNC), which were developed for biomedical applications as a drug-delivery system, have demonstrated beneficial effects on in vitro embryo production studies. LNCs have a core composed of sorbitan monostearate dispersed in capric/caprylic triglyceride. Based on that, we firstly investigated if LNCs supplemented during in vitro oocyte maturation had affinity to the mineral oil placed over the top of the IVM media. Also, the effects of LNC supplementation in different concentrations (0; 0.94; 4.71; 23.56; 117.80 and 589.00µg/mL) during the in vitro maturation protocol were evaluated in oocytes and blastocysts by in vitro tests. LNCs seemed not to migrate to the mineral oil overlay during the in vitro oocyte maturation. Interestingly, LNCs did not show toxic effects in the oocyte in vitro maturation rate, cumulus cells expansion and oocyte viability. The highest LNCs concentration tested (589µg/mL) generated the lowest ROS and GSH levels, and reduced apoptosis rate when compared to the control. Additionally, toxic effects in embryo development and quality were not observed. The LNC supramolecular structure demonstrated to be a promising nanocarrier to deliver molecules in oocytes and embryos, aiming the improvement of the embryo in vitro development.

Prey species of franciscana Pontoporia blainvillei as paratenic hosts of helminths.

The distribution of franciscana Pontoporia blainvillei Gervais & d'Orbigny, 1884, is restricted to the estuarine and coastal waters of the southwestern Atlantic. The diet of this dolphin is composed of fishes, squids, and shrimps, many of which harbor helminths that may infect franciscana. Larval forms of the trematode Synthesium pontoporiae and the acanthocephalan Bolbosoma turbinella have been recorded in franciscana; however, they have not yet been identified in any of the prey species of this cetacean. We evaluated 3 components of the diet of franciscana as possible transmission sources of parasitiasis. Specimens of São Paulo squid Doryteuthis sanpaulensis (n = 50), banded croaker Paralonchurus brasiliensis (n = 43), and rough scad Trachurus lathami (n = 50) were necropsied. Organs were washed and examined under a stereomicroscope. Helminths were collected and mounted on slides. None of the species analyzed showed infection by metacercariae of S. pontoporiae. Helminths found in São Paulo squid have not been recorded in franciscana. Cistacanths of Corynosoma australe were found in the coelomic cavity and mesentery of croaker (prevalence [P] = 53.49%; mean infection intensity [MII] = 6.74) and scad (P = 4%; MII = 1.50). Cistacanths of B. turbinella were also found in the same sites in scad (P = 14%; MII = 2.14). Banded croaker and rough scad are recorded in this study as new paratenic hosts for C. australe, while scad is a new paratenic host for B. turbinella.

The Potential of Nanotechnology in Medically Assisted Reproduction.

Reproductive medicine is a field of science which searches for new alternatives not only to help couples achieve pregnancy and preserve fertility, but also to diagnose and treat diseases which can impair the normal operation of the reproductive tract. Assisted reproductive technology (ART) is a set of methodologies applied to cases related to infertility. Despite being highly practiced worldwide, ART presents some challenges, which still require special attention. Nanotechnology, as a tool for reproductive medicine, has been considered to help overcome some of those impairments. Over recent years, nanotechnology approaches applied to reproductive medicine have provided strategies to improve diagnosis and increase specificity and sensitivity. For in vitro embryo production, studies in non-human models have been used to deliver molecules to gametes and embryos. The exploration of nanotechnology for ART would bring great advances. In this way, experiments in non-human models to test the development and safety of new protocols using nanomaterials are very important for informing potential future employment in humans. This paper presents recent developments in nanotechnology regarding impairments still faced by ART: ovary stimulation, multiple pregnancy, and genetic disorders. New perspectives for further use of nanotechnology in reproductive medicine studies are also discussed.