Assessment of DNA damage in sperm after repeated non-invasive sampling in zebrafish Danio rerio

Type I Diabetes in Zebrafish Reduces Sperm Quality and Increases Insulin and Glucose Transporter Transcripts

Type I diabetes is a prominent human pathology with increasing incidence in the population; however, its cause is still unknown. This disease promotes detrimental effects on reproduction, such as lower sperm motility and DNA integrity. Hence, the investigation of the underlying mechanisms of this metabolic disturbance in reproduction and its transgenerational consequences is of the utmost importance. The zebrafish is a useful model for this research considering its high homology with human genes as well as its fast generation and regeneration abilities. Therefore, we aimed to investigate sperm quality and genes relevant to diabetes in the spermatozoa of Tg(ins:nfsb-mCherry) zebrafish, a model for type I diabetes. Diabetic Tg(ins:nfsb-mCherry) males showed significantly higher expression of transcripts for insulin a (insa) and glucose transporter (slc2a2) compared to controls. Sperm obtained from the same treatment group showed significantly lower sperm motility, plasma membrane viability, and DNA integrity compared to that from the control group. Upon sperm cryopreservation, sperm freezability was reduced, which could be a consequence of poor initial sperm quality. Altogether, the data showed similar detrimental effects related to type I diabetes in zebrafish spermatozoa at the cellular and molecular levels. Therefore, our study validates the zebrafish model for type I diabetes research in germ cells.

Oxidative Stress and DNA Damage of Zebrafish Sperm at Different Stages of the Cryopreservation Process

Although gamete cryopreservation has facilitated advancement of reproduction research by allowing the storage of cells over prolonged periods of time, during freezing-thawing cycles, cells inevitably suffer from cryoinjuries. Here, we evaluate oxidative stress and DNA damage of zebrafish sperm at different stages of the cryopreservation process. It was generally observed that the freezing and thawing of the samples led to an increase in the generation of reactive oxygen species and the activity of the catalase enzyme and a reduction in the generation of sulfhydryl groups and superoxide dismutase activity. The alkaline comet assay demonstrated that DNA damage increased after equilibration time, with an even greater increase after freezing and thawing. The comet assay modified with the enzyme formamidopyrimidine glycosylase, and Endonuclease III demonstrated greater DNA damage than the standard comet assay, demonstrating a high degree of oxidation of purines and pyrimidines at all stages of cryopreservation. Our results show that the freeze and thaw processes cause greater oxidative stress and DNA damage than cryoprotectant toxicity during exposure at the equilibrium stage.

Skim milk powder used as a non-permeable cryoprotectant reduces oxidative and DNA damage in cryopreserved zebrafish sperm

Cryoprotectants play a vital role in the cryopreservation process, protecting biological samples from freezing damage. Here, we evaluate the effects of the combination and interaction of different extenders with permeable and non-permeable cryoprotectants, on the cryopreservation of Danio rerio sperm, analyzing the effects of cryopreservation through a broad approach to variables. Two extenders were used, Hank's balanced salt solution (HBSS) and Ginsburg's solution. Eight cryoprotective solutions (CS) were used: CS1 (HBSS + Me₂SO 8%), CS2 (HBSS + Methanol 8%), CS3 (HBSS + Me₂SO 8% + Skim milk powder 15%), CS4 (HBSS + Methanol 8% + Skim milk powder 15%), CS5 (Ginsburg + Me₂SO 8%), CS6 (Ginsburg + Methanol 8%), CS7 (Ginsburg + Me₂SO 8% + Skim milk powder 15%) and CS8 (Ginsburg + Methanol 8% + Skim milk powder 15%). The samples were cryopreserved in cryovials for 20 min on dry ice, stored in liquid nitrogen, thawed at 38 °C for 10 s, and analyzed. In addition to increasing viability, we show that powdered milk also allows for better preservation of the membrane and normal cell morphology, and protects the sperm cells from DNA damage and oxidative stress caused by cryopreservation.

Transcriptomic responses to pollution in natural riverine environment in Rita rita

Aquatic pollution is one of the most common threats to the ecological health of aquatic ecosystems and its biota. Fish as lower vertebrates are excellent model to study the impact and responses of aquatic pollution. In fish, gill is the main organ indicator of whole animal health as it comes in contact with the surrounding water and absorbs many pollutants and contaminants; therefore, investigations on alterations in fish gill at transcriptome level could provide newer insights to the stress response mechanism(s) and pathways. For comprehensive evaluation of the impacts of pollutants (joint toxicity) prevalent in the riverine environment, comparative transcriptome analysis, by Next Generation Sequencing under Illumina HiSeq 2500 platform, was carried out in gill tissues of Rita rita collected from two stretches of river Ganga (Kanpur and Farakka) and results were validated by RT-qPCR. Out of 154,077 unigenes (Accession SRR548008), a total of 2024 differentially expressed genes (DEGs) including 942 up-regulated and 1082 down-regulated genes were identified by DESeq program. Further, Gene Ontology (GO) of DEGs showed that ribosomal large subunit biogenesis, mitochondrial ribosome and box H/ACA SnoRNA binding categories are highly affected by pollution. Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis showed the involvement of the DEGs in energy metabolism, translational and transcriptional machinery, protein folding and degradation suggesting that these signalling pathways are highly affected by aquatic pollution. Among the DEGs, up-regulation of cytochrome c oxidase subunit (cox) 7a2 (69.47 fold), hsp70 subunit 14 (hsp70-14, 5.27 fold), muscle related coiled-coil protein (MURC, 21.55 fold), lysozyme G (40.14 fold), cox17 (29.36 fold) were the conspicuous ones which showed similar trends in expression when analysed by RT-qPCR. Based on fold change, perturbation values, correlation analysis by PCA and RT-qPCR validation, up-regulation of cox7a2, MURC and hsp70-14 appeared to be the most promising biomarker responses and could be useful in the evaluation of gill health and possibly be extended towards aquatic ecosystem health assessment.

Investigation of Fertilizing Capacity of Zebrafish (Danio rerio) Sperm Exposed to Heavy Metals

The objective of our study was to investigate the effects of heavy metals on the fertilizing capacity of exposed zebrafish sperm, on embryonic survival, and on occurrence of embryonic deformities following fertilization with exposed sperm. It is important to test heavy metals because they are well-known pollutants. Sperm of externally fertilizing species can get in contact with pollutants found in aquatic environment. Zebrafish sperm, despite its advantages, has seldom been used in in vitro toxicological studies and no reports are available regarding the fertilizing capacity of exposed sperm. Zebrafish sperm was stripped and exposed to concentrations of the tested heavy metals (Zn²⁺, Cd²⁺, Cr³⁺, Cu²⁺, Ni²⁺, Hg²⁺, As³⁺) for 30 or 120 minutes. Calculated half-maximal effective concentration (EC₅₀) values do not differ significantly from those calculated for motility for any of the tested heavy metals, which means fertilization rate can indicate the toxicity of the given substance following exposure of sperm. Thus, its application as in vitro toxicological end point is reasonable. The survival of embryos and embryonic development have not been affected by the exposure of spermatozoa, which means all alterations in spermatozoa caused by heavy metals have been expressed before 24 hours post fertilization.

Selection Criteria of Zebrafish Male Donors for Sperm Cryopreservation

Selection criteria for sperm cryopreservation are highly relevant in zebrafish since sperm quality is particularly variable in this species. Successful cryopreservation depends on high-quality sperm, which can only be ensured by the selection of breeders. Consequently, male selection and management are a priority to improve cryopreservation, and therefore, this study aimed to characterize optimal age and sperm collection frequency in zebrafish. For this purpose, males from wild type (AB) and from a transgenic line [Tg(runx2:eGFP)] were sampled at 6, 8, 12, and 14 months. For each age, sperm were collected at time 0 followed by samplings at 2, 7, and 14 days of rest. Sperm quality was assessed according to motility and membrane viability parameters. Quality assessment showed that Tg(runx2:eGFP) displayed significantly higher motility than AB and younger males showed higher motility in both lines. Sperm collection frequency affected membrane viability. While AB fish recovered sperm viability after 14 days of rest, Tg(runx2:eGFP) could not recover. Consequently, it may be important to study the sperm quality of each zebrafish line before sperm cryopreservation. Taking into consideration the results achieved in both lines, sperm collection should be performed between 6 and 8 months of age with a minimum collection interval of 14 days.

Electric ultrafreezer (- 150 °C) as an alternative for zebrafish sperm cryopreservation and storage

Zebrafish sperm cryopreservation is a fundamental methodology to manage and back-up valuable genetic resources like transgenic and mutant strains. Cryopreservation usually requires liquid nitrogen for storage, which is expensive and hazardous. Our objective was to evaluate if electric ultrafreezers (- 150 °C) are a viable alternative for zebrafish sperm storage. Zebrafish sperm was cryopreserved in the same conditions (- 20 °C/min), stored either in liquid nitrogen or in an ultrafreezer, and thawed after 1 week, 1 month, and 3 months. Sperm motility, membrane integrity, and fertilization ability were assessed. There were no significant differences in motility and hatching rate throughout storage time. Additionally, we aimed at understanding if cryopreservation directly in an ultrafreezer (- 66 °C/min) could improve post-thaw sperm quality. Freezing at - 20 °C/min was performed as before, and compared to samples cryopreserved with a fast cooling rate by placing directly in an ultrafreezer (- 66 °C/min). Sperm quality was assessed according to motility, viability, DNA fragmentation, and apoptosis (annexin V). The - 66 °C/min cooling rate showed significantly higher membrane and DNA integrity, and lower number of cells in late apoptosis in comparison to the other treatments. This study showed that zebrafish sperm cryopreservation and storage in an ultrafreezer system is possible and a fast cooling rate directly in ultrafreezer improves post-thaw sperm quality.

Effect of different oxidative stress degrees generated by hydrogen peroxide on motility and DNA fragmentation of zebrafish (Danio rerio) spermatozoa

An increase in reactive oxygen species (ROS) or decrease in antioxidant barriers can provoke lipid peroxidation of the membranes or DNA damage of the spermatozoa. The aim of this work is to study the effect of the different degrees of oxidative stress generated by H₂ O₂ incubation on total motility, kinetics, and DNA fragmentation of zebrafish (Danio rerio) spermatozoa. For this process, experimental groups were incubated in 50 µM (Low; L) and 200 µM (High; H) H₂ O₂ , respectively, for 20 min at 4ºC. Sperm motility parameters were obtained with a computer-assisted sperm analysis (CASA) system. Sperm DNA fragmentation (SDF) was assessed using the sperm chromatin dispersion test. Both low and high H₂ O₂ concentration groups showed lower motility than control groups. Progressive motility of spermatozoa incubated in the H group dropped rapidly in comparison with other groups. Regarding SDF, the control and L groups had significantly lower values than the H group (25.0% and 31.6% vs. 48.1% fragmented sperm for C, L, and H groups, respectively; p < 0.05). Sperm motility, mostly progressive motility, decreased as H₂ O₂ concentration increased, mainly when time after sperm activation increased. SDF increased as the H₂ O₂ concentration increased. However, measurements of the halo area did not agree with the subjective SDF rate.

Expression patterns and mutation analysis of p53 in fish Rita rita from polluted riverine environment

The present study was undertaken to investigate the alterations in gene expression patterns and for mutation analysis of p53 in the riverine catfish Rita rita collected from polluted riverine habitat. The partial p53 gene sequence of Rita rita generated showed a high degree of similarities with the DNA binding domains of fishes, mice and human. Transcriptomic analysis, carried out by quantitative real-time Polymerase Chain Reaction (RT-qPCR), showed significant down-regulation of p53 in fishes collected from most of the polluted stretches. Similar trend in protein abundance was observed by western blot analysis. Down-regulation of p53 was more pronounced in gill than liver. Expression patterns of p53 suggest that exposure to a multitude of contaminants in the natural riverine ecosystem could suppress the expression of p53. Genomic DNA showed a low stained smear pattern upon electrophoresis, with no evidence of DNA fragmentation. For mutation analysis PCR-SSCP followed by sequence analysis was carried out, which identified eight mutations; two at codon level and six missense mutations in the DNA binding domain IV and V. Secondary structure prediction showed that these mutations could lead to impairment of protein structure. Thus, the present study indicated that aquatic pollution has impacted these lower vertebrates which are reflected by the down-regulation of tumor suppressor protein (p53) in majority of the stretches studied.