Male exposure to bisphenol a impairs spermatogenesis and triggers histone hyperacetylation in zebrafish testes.

Bisphenol A (BPA) is an endocrine disruptor whose ubiquitous presence in the environment has been related with impairment of male reproduction. BPA can cause both transcriptomic and epigenetic changes during spermatogenesis. To evaluate the potential effects of male exposure to BPA, adult zebrafish males were exposed during spermatogenesis to doses of 100 and 2000 µg/L, which were reported in contaminated water bodies and higher than those allowed for human consumption. Fertilization capacity and survival at hatching were analysed after mating with untreated females. Spermatogenic progress was analysed through a morphometrical study of testes and apoptosis was evaluated by TUNEL assay. Testicular gene expression was evaluated by RT-qPCR and epigenetics by using ELISA and immunocytochemistry. In vitro studies were performed to investigate the role of Gper. Chromatin fragmentation and the presence of transcripts were also evaluated in ejaculated sperm. Results on testes from males treated with the highest dose showed a significant decrease in spermatocytes, an increase in apoptosis, a downregulation of ccnb1 and sycp3, all of which point to an alteration of spermatogenesis and to meiotic arrest and an upregulation of gper1 and esrrga receptors. Additionally, BPA at 2000 µg/L caused missregulation of epigenetic remodelling enzymes transcripts in testes and promoted DNA hypermethylation and H3K27me3 demethylation. BPA also triggered an increase in histone acetyltransferase activity, which led to hyperacetylation of histones (H3K9ac, H3K14ac, H4K12ac). In vitro reversion of histone acetylation changes using a specific GPER antagonist, G-36, suggested this receptor as mediator of histone hyperacetylation. Males treated with the lower dose only showed an increase in some histone acetylation marks (H3K14ac, H4K12ac) but their progeny displayed very limited survival at hatching, revealing the deleterious effects of unbalanced paternal epigenetic information. Furthermore, the highest dose of BPA led to chromatin fragmentation, promoting direct reproductive effects, which are incompatible with embryo development.

Distribution of DNA damage in the sperm nucleus: A study of zebrafish as a model of histone-packaged chromatin.

Reproductive defects can occur when the integrity of the male gamete genome is affected. Sperm chromatin is not homogeneous, having relaxed regions which are more accessible to the transcription machinery in the embryo, and thought to be specially sensitive to DNA damage. The level of damage in specific genes located in these sensitive regions could represent an early biomarker of damage. Our objective is to test the hypothesis that these more relaxed regions show greater susceptibility to damage in zebrafish, a species lacking protamines and whose sperm chromatin is compacted with histones. After sperm UV irradiation, treatment with H2O2 and cryopreservation, global chromatin fragmentation was evaluated using the TUNEL assay, and the number of lesions per 10 Kb in specific genes (hoxa3a, hoxb5b, sox2, accessible for early transcription and rDNA 18S and rDNA 28S) was quantified by using a qPCR approach. Additionally, oxidative damage within the sperm nucleus and the potential colocalization of this injury with histone H3 and TOPO IIα+ß were located by using immunofluorescence. UV irradiation produced the highest degree of fragmentation (p = 0.041) and the highest number of lesions per 10 Kb in all the genes, but no differences were observed in sensitivity to damage in the studied genes (ranging from 14.93 to 8.03 lesions per 10 Kb in hoxb5b and 28S, respectively). In contrast, H2O2 and cryopreservation caused varying levels of damage in the analyzed genes which was not related to their accessibility, ranging from 0.00 to 1.65 lesions per 10 Kb in 28S and hoxb5b, respectively, after H2O2 treatment, and from 0.073 to 5.51 in 28S and sox2, respectively, after cryopreservation. Immunodetection near oxidative lesions also revealed different spatial patterns depending on the treatments used, these being mostly homogeneous with UV irradiation or cryopreservation, and peripherally located around the nucleus after H2O2 treatment. Oxidative lesions did not colocalize with histone H3 or TOPO IIα+ß, thus demonstrating that the relaxed DNA regions associated with these proteins were not more vulnerable to oxidative damage. Results suggest that accessibility of each agent to the nucleus could be the main factor responsible for the distribution of sperm DNA damage rather than the organization of the chromatin. Lesions in these genes important to early embryo development assayed in this study cannot be used as biomarkers of global DNA damage.

Probiotic administration improves sperm quality in asthenozoospermic human donors.

The objective of this study is to analyse the effect of the ingestion of two selected antioxidant probiotics strains (Lactobacillus rhamnosus CECT8361 and Bifidobacterium longum CECT7347) on sperm quality parameters in asthenozoospermic males after three and six weeks of administration. Nine asthenozoospermic men without any medical treatment under similar diet conditions participated in the study. The quality of individual sperm samples was evaluated before (previous to ingestion), during (after 3 and 6 weeks of ingestion) and after probiotic administration (3 and 6 weeks after finishing the treatment). Sperm motility was evaluated by computer-assisted sperm analysis system, DNA fragmentation by sperm chromatin structure assay, cell viability by flow cytometry and measurement of intracellular H2O2 (reactive oxygen species; ROS) by flow cytometry using dichloro-dihydrofluorescein diacetate. Sperm motility was drastically improved after the treatment (approximately 6 fold change), DNA fragmentation was statistically reduced after probiotic administration from (approximately 1.2 fold change) and intracellular H2O2 level was decreased (approximately 3.5 fold change). Cell viability was not affected by the treatment. The significant improvement in sperm motility and the decrease in DNA fragmentation reported in this study provide preliminary evidence that probiotics could be administrated to improve motility and decrease DNA fragmentation and ROS levels in asthenozoospermic human males.

Selection of nonapoptotic sperm by magnetic-activated cell sorting in Senegalese sole (Solea senegalensis).

Senegalese sole (Solea senegalensis) is a promising species in aquaculture. However, owing to decreased sperm quality in F1 generations and the absence of courtship in those individuals born in captivity, artificial fertilization is being used to generate new progenies. The objective of this study was to implement a sperm selection method for nonapoptotic sperm subpopulation recovery before sperm cryopreservation. In particular, magnetic-activated cell sorting is used to eliminate apoptotic spermatozoa. This study represents the proof-of-concept for magnetic-activated cell sorting applicability in teleost species relevant in aquaculture. Apoptotic cell population was studied by flow cytometry using YO-PRO-1 and a caspase detection kit. Also, reactive oxygen species were measured in sperm samples. Our data demonstrated that caspase detection is more specific than YO-PRO-1 in the identification of apoptotic cells in S senegalensis seminal samples. The results showed that the percentage of apoptotic cells (caspase positive) was significantly higher (P = 0.04) in seminal samples from F1 than that from wild individuals. Magnetic-activated cell sorting removed a significant number of apoptotic cells from the samples (54% and 75% in wild and F1 individuals, respectively), decreasing the level of cells positive for reactive oxygen species (P = 0.17). In conclusion, this technique reduces the percentage of nonfunctional spermatozoa in a seminal sample before cryopreservation. This novel technique can be applied directly in the aquaculture industry.

Impact of sperm DNA damage and oocyte-repairing capacity on trout development.

Zygotic repair of paternal DNA is essential during embryo development. In spite of the interest devoted to sperm DNA damage, its combined effect with defect-repairing oocytes has not been analyzed. Modification of the breeding season is a common practice in aquaculture. This practice reduces developmental success and could affect the both factors: sperm DNA integrity and oocyte repair capacity. To evaluate the maternal role, we analyzed the progeny outcome after fertilizing in-season trout oocytes with untreated and with UV-irradiated sperm. We also analyzed the offspring obtained out of season with untreated sperm. The analysis of the number of lesions in 4 sperm nuclear genes revealed an increase of 1.22-11.18 lesions/10 kb in out-of-season sperm, similar to that obtained after sperm UV irradiation (400 µW/cm(2)5 min). Gene expression showed in out-of-season oocytes the overexpression of repair genes (ogg1, ung, lig3, rad1) and downregulation of tp53, indicating an enhanced repairing activity and reduced capacity to arrest development upon damage. The analysis of the progeny in out-of-season embryos revealed a similar profile tolerant to DNA damage, leading to a much lower apoptotic activity at organogenesis, lower hatching rates and increased rate of malformations. The effects were milder in descendants from in-season-irradiated sperm, showing an enhanced repairing activity at epibolia. Results point out the importance of the repairing machinery provided by the oocyte and show how susceptible it is to environmental changes. Transcripts related to DNA damage signalization and repair could be used as markers of oocyte quality.

Inhibition of zygotic DNA repair: transcriptome analysis of the offspring in trout (Oncorhynchus mykiss).

Zygotic repair of the paternal genome is a key event after fertilization. Spermatozoa accumulate DNA strand breaks during spermatogenesis and can suffer additional damage by different factors, including cryopreservation. Fertilization with DNA-damaged spermatozoa (DDS) is considered to promote implantation failures and abortions, but also long-term effects on the progeny that could be related with a defective repair. Base excision repair (BER) pathway is considered the most active in zygotic DNA repair, but healthy oocytes contain enzymes for all repairing pathways. In this study, the effects of the inhibition of the BER pathway in the zygote were analyzed on the progeny obtained after fertilization with differentially DDS. Massive gene expression (GE; 61 657 unique probes) was analyzed after hatching using microarrays. Trout oocytes are easily fertilized with DDS and the high prolificacy allows live progeny to be obtained even with a high rate of abortions. Nevertheless, the zygotic inhibition of Poly (ADP-ribose) polymerase, upstream of BER pathway, resulted in 810 differentially expressed genes (DEGs) after hatching. DEGs are related with DNA repair, apoptosis, telomere maintenance, or growth and development, revealing a scenario of impaired DNA damage signalization and repair. Downregulation of the apoptotic cascade was noticed, suggesting a selection of embryos tolerant to residual DNA damage during embryo development. Our results reveal changes in the progeny from defective repairing zygotes including higher malformations rate, weight gain, longer telomeres, and lower caspase 3/7 activity, whose long-term consequences should be analyzed in depth.

Subpopulation pattern of eel spermatozoa is affected by post-activation time, hormonal treatment and the thermal regimen.

There has been a marked reduction in natural stocks of eels (genus Anguilla) over the past 60 years, and the culture of eels is still based on the capture of very large quantities of juveniles. It is necessary to close the life cycle in captivity in order to ease the pressure on wild populations. The aims of the present study were to evaluate sperm subpopulations (through cluster analysis of computer-aided sperm analysis data) in the European eel (Anguilla anguilla) and to assess the effects of motility acquisition time after activation (i.e. at 30, 60 and 90s), the thermal regimen (i.e. 10°C (T10) or 15°C (T15) and up to 20°C, or constant at 20°C (T20)) and hormonal treatments (i.e. human chorionic gonadotropin (hCG), recombinant (r) hCG or pregnant mare serum gonadotropin (PMSG)) on these subpopulations. In all cases, we obtained three subpopulations of spermatozoa: low velocity and linear (S1); high velocity with low linearity (S2); and high velocity and linear (S3; considered high quality). Total motility and S1 were affected by acquisition time; thus, 30s is recommended as the standard time for motility acquisition. When eels were kept at 20°C (T20), motility data fitted quadratic models, with the highest motility and proportion of S3 between Weeks 8 and 12 after the first injection. Lower temperatures (T10, T15) delayed spermiation and the obtaining of high-quality spermatozoa (S3), but did not seem to alter the spermiation process (similar subpopulation pattern). Conversely, the hormonal treatments altered both the dynamics of the subpopulation pattern and the onset of spermiation (with PMSG delaying it). Total motility and the yield of S3 with the widely used hCG treatment varied throughout the spermiation period. However, using rhCG allowed us to obtain high-quality and constant motility for most of the study (Weeks 7-20), and the S3 yield was also higher overall (61.8±1.3%; mean ± s.e.m.) and more stable over time than the other hormonal treatments (averaging 53.0±1.4%). Using T20 and rhCG would be more economical and practical, allowing us to obtain a higher number of S3 spermatozoa over an extended time.

Analysis of DNA damage after human sperm cryopreservation in genes crucial for fertilization and early embryo development.

Sperm cryopreservation is widely used in clinic for insemination, in vitro fertilization and other procedures such as intracytoplasmic sperm injection. The assessment after freezing/thawing of spermatozoa viability, motility and sometimes DNA integrity (mainly using fragmentation assays) has been considered enough to guarantee the safety and effectiveness of the technique. However, it is known that, even when fragmentation is absent, a significant DNA damage could be detected in some genome regions. This is particularly important considering that, during the last years, several studies have pointed out the importance of key paternal genes in early embryo development. In this study, using normozoospermic donors, we present a candidate gene approach in which we quantify the number of lesions produced by freezing/thawing over key genes (PRM1, BIK, FSHB, PEG1/MEST, ADD1, ARNT, UBE3A, SNORD116/PWSAS) using quantitative PCR. Our results demonstrated that the cryopreservation protocol used, which is routinely employed in clinic, produced DNA lesions. The genes studied are differentially affected by the process, and genome regions related to Prader-Willi and Angelman syndromes were among the most damaged: SNORD116/PWSAS (4.56 ± 1.84 lesions/10 kb) and UBE3A (2.22 ± 1.3 lesions/10 kb). To check if vitrification protocols could reduce these lesions, another experiment was carried out studying some of those genes with higher differences in the first study (FSHB, ADD1, ARNT and SNORD116/PWSAS). The number of lesions was not significantly reduced compared to cryopreservation. These results could be relevant for the selection of the most adequate available cryopreservation protocol in terms of the number of lesions that produced over key genes, when no differences with other traditional techniques for DNA assessment could be detected.

Effect of cryopreservation on human sperm messenger RNAs crucial for fertilization and early embryo development.

During recent years, several studies have pointed out the importance of key paternal transcripts in early embryo development. Sperm cryopreservation is commonly applied in assisted reproductive technologies (ARTs) and it is important to know if it produces any relevant effect at this level. In this study, using normozoospermic donors, we present a candidate transcript approach in which we quantify the presence of sperm mRNAs considered as markers for male fertility and pregnancy success. Analyses were done using quantitative PCR. Our results demonstrated that the used cryopreservation protocol, which is routinely employed in clinical practice, alter transcripts considered as spermatozoa quality markers and markers for pregnancy success. Most of the studied transcripts considered as male quality markers (PRM1, PRM2, and PEG1/MEST) and one of studied mRNAs reported as markers of pregnancy success (ADD1) were reduced after cryopreservation. In order to check if vitrification protocols could reduce this alteration, another assay was carried out analyzing those transcripts with higher differences in the first study (PRM1 and PRM2). The results showed the same tendency. Although maternal mRNAs can compensate these deficiencies, these results could make advisable the optimization of freezing/thawing procedures.

Sea bass sperm freezability is influenced by motility variables and membrane lipid composition but not by membrane integrity and lipid peroxidation.

Cryopreserved sperm quality depends on the characteristics of fresh sperm. Thus, it is necessary to establish a group of variables to predict the cryopreservation potential of the fresh samples with the aim of optimizing resources. Motility, viability, lipid peroxidation and lipid profile of European sea bass (Dicentrarchus labrax) sperm were determined before and after cryopreservation to establish which variables more accurately predict the sperm cryopreservation potential in this species. Cryopreservation compromised sperm quality, expressed as a reduction of motility (46.5 ± 2.0% to 35.3 ± 2.5%; P<0.01) and viability (91.3 ± 0.7% to 69.9 ± 1.6%; P<0.01), and produced an increase in lipid peroxidation (2.4 ± 0.4 to 4.0 ± 0.4 µmoles MDA/mill spz; P<0.01). Also, significant changes were observed in the lipid composition before and after freezing, resulting in a reduction in the cholesterol/phospholipids ratio (1.4 ± 0.1 to 1.1 ± 0.0; P<0.01), phosphatidylcholine (47.7 ± 0.8% to 44.2 ± 0.8%; P<0.01) and oleic acid (8.7 ± 0.2% to 8.3 ± 0.2%; P<0.05) in cryopreserved sperm, as well as an increase in lysophosphatidylcholine (4.4 ± 0.3% to 4.8 ± 0.3%; P<0.01) and C24:1n9 fatty acid (0.5 ± 0.1% to 0.6 ± 0.1%; P<0.05). Motility, velocity, cholesterol/phospholipids ratio, monounsaturated fatty acids and the n3/n6 ratio were positively correlated (P<0.05) before and after freezing, whereas, viability and lipid peroxidation were not correlated. Motility and the cholesterol/phospholipids (CHO/PL) ratio were negatively correlated (P<0.05) with each other and the CHO/PL ratio was positively correlated (P<0.05) with lipid peroxidation. Therefore, the results demonstrated that motility and plasma membrane lipid composition (CHO/PL) were the most desirable variables determined in fresh samples to predict cryo-resistance in European sea bass sperm, taking into account the effect of both on cryopreserved sperm quality.

Incorporation of ascorbic acid and α-tocopherol to the extender media to enhance antioxidant system of cryopreserved sea bass sperm.

Despite the overwhelming application of sperm cryopreservation in aquaculture and broodstock management, its detrimental effects on sperm quality must be taken into account. Imbalance of reactive oxygen species is considered one of the main triggers of cell damage after cryopreservation, because the spermatozoa antioxidant system is decimated during this process, mainly because the natural antioxidants present in seminal plasma diminish when sperm is diluted in extenders. It has been demonstrated that the addition of antioxidants to the extender improves the quality of thawed sperm. Thus, the aim of the present work was to evaluate the status of the antioxidant system in cryopreserved sea bass sperm, and the possibility of enhancing this system to reduce oxidation of the membrane compounds by extender supplementation with vitamins. To do this, sperm from European sea bass (Dicentrarchus labrax) was cryopreserved using an extender control (NAM), supplemented with 0.1 mm α-tocopherol or 0.1 mm ascorbic acid. Sperm motility (computer assisted sperm analysis (CASA) parameters), viability (SYBR Green/propidium iodide (PI)), lipid peroxidation (malondialdehyde (MDA) levels) and protein oxidation (DNPH levels) were analyzed, as well as the status of the sperm antioxidant system by determining glutathione peroxidase, glutathione reductase and superoxide dismutase (GPX, GSR and SOD) activity. The results demonstrated that extenders containing vitamins significantly increased sperm motility. Total motility, velocity and linearity increased from 31.2 ± 3.0 µm/sec, 18.3 ± 1.7 µm/sec and 46.9 ± 2.0% in extender containing 0.1 mm α-tocopherol or 30.6 ± 3.9 µm/sec, 19.5 ± 1.6 µm/sec and 47.9 ± 2.2% in extender containing 1 mm ascorbic acid respect to the extender control (20.7 ± 3.3 µm/sec, 13.8 ± 1.7 µm/sec and 37.3 ± 4.1%). However, viability and levels of lipid peroxidation and protein oxidation were not affected by the presence of these antioxidants, suggesting that membrane impairment could be more associated to osmotic shock or membrane destabilization than oxidative damage. The increased activity of both GPX and GSR after cryopreservation showed that the antioxidant system of sea bass sperm must play an important role in preventing oxidation of the membrane compounds. In conclusion, the addition of α-tocopherol and ascorbic acid to the extender media, together with the antioxidant system of the spermatozoa improved sea bass sperm motility, which is one of the impairment parameters most affected by cryopreservation.

Altered gene transcription and telomere length in trout embryo and larvae obtained with DNA cryodamaged sperm.

Sperm cryopreservation could entail DNA damage, promoting base oxidization and strand breaks. In a previous work we showed that trout DNA damaged sperm is able to fertilize leading to embryo loss when the repair system of the oocyte is inhibited. Here we have analysed the later effects on embryo and larvae of fertilizing trout oocytes with cryopreserved DNA-damaged spermatozoa. Fish have weak sperm selection mechanisms, are very prolific and have external embryo development, being convenient models for this type of study. We cryopreserved rainbow trout semen using extenders containing egg yolk or their low density lipoprotein fraction to obtain samples with different degrees of DNA damage. DNA fragmentation was evaluated using the Comet assay and telomere length using quantitative-PCR. Fertilization trials were performed and the transcription at different developmental stages of telomerase reverse transcriptase (Tert) and eight genes related with embryo growth and development (Igf1, Igf2, Igfr1a, Igfr1b, Gh1, Gh2, Ins1 and Ins2) were analyzed using quantitative-PCR in surviving embryos and larvae. Results showed an increase in sperm DNA fragmentation after both cryopreservation procedures as well as a decrease in sperm telomere length. Larvae obtained with damaged sperm showed longer telomeres and Tert overexpression. The transcription of the analyzed genes in these embryos and larvae was also modified with respect to the control, most of them as an increase at hatch. We conclude that fertilization with cryopreserved DNA-damaged spermatozoa significantly affects offspring performance, detectable as an increase in telomere length as well as some alterations in gene expression in surviving embryo and larvae.

Changes in Solea senegalensis sperm quality throughout the year.

Some of the Senegalese sole (Solea senegalensis) broodstock reproductive constraints are related to sperm quality. Although they present two defined spawning season (spring and autumn), males gave semen during all the year thus an exhaustive annual sperm analysis is important to determine the seasonal changes in semen quality. Sampling was performed monthly during one year, analyzing different cellular parameters to better understand sperm quality limitations obstructing sole mass production. The percentage of progressive motile cells and their linear velocity showed a decrease from March (beginning of the first spawning season) to July (when the highest temperatures were observed), followed by a slight increase in August and October (second spawning season). DNA fragmentation values showed highest values between the two spawning seasons and decreased to the end of the year. The percentage of apoptotic cells was lowest in March (beginning of the first spawning season) and the highest in November. The percentage of cells resistant to seawater exposure presented two peaks related with both spawning seasons. There was a tendency for the semen to attain a quality peak between the beginning and the middle of the first spawning season (March-May), followed by a pronounced decrease, achieving the lowest values during the months with the highest temperature. Also, the different males present in the broodstocks reach their sperm quality peak at different times, which will result in an unequal contribution for the next generation.

Effect of cryopreservation on fish sperm subpopulations.

The evaluation of the motility data obtained with a CASA system, applying a Two-Step Cluster analysis, identified in seabream sperm 3 different sperm subpopulations that correlated differently with embryo hatching rates. Hence, we designed an experiment to understand the effect of the application of different cryopreservation protocols in these sperm motility-based subpopulations. We analyzed Sparus aurata frozen/thawed semen motility 15, 30, 45 and 60s after activation, using CASA software. Different protocols were applied for cryopreservation: three different cryoprotectants (Dimethyl Sulfoxide (Me(2)SO), Ethylene Glycol (EG) and Propylene Glycol (PG)) each at two different concentrations and two packaging volumes (0.5ml straws, and 1.8ml cryovials) were tested. Different freezing rates were evaluated corresponding to 1, 2, 3, 4 and 8cm above the liquid nitrogen surface for the straws and 1, 2 and 4cm for the cryovials. Motility parameters rendered by CASA were treated with a Two-Step Cluster analysis. Three different subpopulations were obtained: SP1 - slow non-linear spermatozoa, SP2 - slow linear spermatozoa and SP3 - fast linear spermatozoa. We considered SP3 as the subpopulation of interest and focused further analyses on it. Generally, SP3 was the best represented subpopulation 15s after activation and was also the one showing a greater decrease in time, being the least represented after 60s. According to the applied univariate general linear model, samples frozen in straws with 5% Me(2)SO and in cryovials with 10% Me(2)SO at 2 and 1cm from the LN(2,) respectively, produced the best results (closer to the control). Clustering analysis allowed the detection of fish sperm subpopulations according to their motility pattern and showed that sperm composition in terms of subpopulations was differentially affected by the cryopreservation protocol depending on the cryoprotectant used, freezing rates and packaging systems.

Evaluation of DNA damage as a quality marker for rainbow trout sperm cryopreservation and use of LDL as cryoprotectant.

Defining reliable and objective biomarkers of sperm quality is a complex matter, because it does not rely on a particular characteristic of the milt. Susceptibility to cryopreservation varies between ejaculations and throughout the year, and the evaluation of fresh sperm does not always provide accurate information about their fertilization ability after freezing and thawing. DNA is one of the cell components prone to suffering cryodamage and several studies have pointed out the importance of the maintenance of its integrity during sperm cryostorage. The authors analysed sperm from rainbow trout for four weeks during the natural reproductive season. Viability, DNA integrity, and fertilization ability were evaluated. Furthermore, in order to increase membrane and DNA protection during sperm cryopreservation, the authors optimized the use of LDL fraction from egg yolk as a cryoprotectant during the analysed period. Results revealed that the evaluation of DNA damage in fresh sperm reveals subtle cell damage, not evidenced in fresh sperm by the other parameters. DNA fragmentation increased from 8 to 31% during the reproductive season, indicating pre-freezing differences that render the cells more susceptible to cryodamage. Also, the use of 12% LDL (low density lipoprotein) fraction, instead of the commonly used pure egg yolk, improved sperm quality after freezing. When LDL was used, post-thaw quality remained constant throughout the analysed period, providing around 60% of eyed embryos. In contrast, when egg yolk was used, post-thaw quality decreased significantly at the end of the season and the percentage of eyed embryos dropped from 60% to 27%. Results demonstrated that reduction in DNA integrity takes place during the reproductive season affecting susceptibility to cryodamage and that the protective effect of egg yolk is very much improved when only their LDL fraction is added to the cryopreservation extender.

Fertilization capacity with rainbow trout DNA-damaged sperm and embryo developmental success.

Mammalian spermatozoa undergo a strong selection process along the female tract to guarantee fertilization by good quality cells, but risks of fertilization with DNA-damaged spermatozoa have been reported. In contrast, most external fertilizers such as fish seem to have weaker selection procedures. This fact, together with their high prolificacy and external embryo development, indicates that fish could be useful for the study of the effects of sperm DNA damage on embryo development. We cryopreserved sperm from rainbow trout using egg yolk and low-density lipoprotein as additives to promote different rates of DNA damage. DNA fragmentation and oxidization were analyzed using comet assay with and without digestion with restriction enzymes, and fertilization trials were performed. Some embryo batches were treated with 3-aminobenzamide (3AB) to inhibit DNA repair by the poly (ADP-ribose) polymerase, which is an enzyme of the base excision repair pathway. Results showed that all the spermatozoa cryopreserved with egg yolk carried more than 10% fragmented DNA, maintaining fertilization rates of 61.1+/-2.3 but a high rate of abortions, especially during gastrulation, and only 14.5+/-4.4 hatching success. Furthermore, after 3AB treatment, hatching dropped to 3.2+/-2.2, showing that at least 10% DNA fragmentation was repaired. We conclude that trout sperm maintains its ability to fertilize in spite of having DNA damage, but that embryo survival is affected. Damage is partially repaired by the oocyte during the first cleavage. Important advantages of using rainbow trout for the study of processes related to DNA damage and repair during development have been reported.

Sperm quality evaluation in Solea senegalensis during the reproductive season at cellular level.

Sperm quality seems to be one of the reasons for the reproduction constraints faced by Senegalese sole (Solea senegalensis) aquaculturists. Previous studies in this species indicated that the sperm quality of individuals kept in culture varies throughout the year and that different sperm subpopulations can be identified in ejaculates according to the motility pattern of spermatozoa. Aiming to better understand factors affecting sole sperm quality in captivity, sperm of 11 males was assessed during the reproductive season using different parameters: motility characteristics using CASA analysis; cell plasma membrane resistance to seawater hyperosmolarity; DNA fragmentation with single-cell gel electrophoresis; and early apoptosis, labeled with Annexin-V FITC. Computer-assisted sperm analyses motility data were treated using multivariate analysis to identify the presence of different spermatozoa subpopulations according to their motility pattern. Four distinct sperm subpopulations were obtained: Subpop1, which includes fast linear spermatozoa; Subpop2, made up of fast nonlinear spermatozoa; Subpop3, which includes slow linear spermatozoa; and Subpop4, which contains slow nonlinear spermatozoa. The sperm subpopulation structure varied with time after activation and with male. Low cell resistance to the seawater hyperosmotic conditions was noticed. The Annexin-V assay allowed the identification of an apoptotic population ranging from 6% to 20%. A high percentage of cells (64.1%) showed a DNA fragmentation level below 30%, but these values varied significantly between males. DNA fragmentation appears to be related to cell membrane resistance to hyperosmotic conditions faced by the cells when in contact with seawater. This condition seems to modulate the composition of the motile sperm population and performance after activation. This phenomenon could be related to the spermatozoa maturation process.

Cryoprotective effects of antifreeze proteins delivered into zebrafish embryos.

Fish embryo cryopreservation, which is useful in aquaculture or biodiversity conservation, is still far from being achieved. Structural barriers reduce the entrance of cryoprotectants into embryo compartments. Previous studies demonstrated a better ability for freezing in Arctic species which naturally express antifreeze proteins (AFPs). In this study, AFPs were delivered in early zebrafish embryos by incubation in media containing protein. Their cryoprotective effects were then analyzed. Chilling sensitivity was evaluated at 4 degrees C and -10 degrees C. Survival rates significantly increased in embryos incorporating AFPI and kept at -10 degrees C. To analyze their effects on cryopreservation, 5-somite embryos were vitrified. Incorporation of AFPI reduced the percentage of embryos that collapsed at thawing (14.2% of AFPI-treated embryos and 48.9% of controls). Cellular damage caused by vitrification was assessed after thawing by cell dissociation and further analysis of cell survival in culture (SYBR-14/IP labeling). The percentage of viable cells at thawing ranged from 25 to 50%, considered incompatible with embryo development. Cells recovered from frozen-control embryos did not survive in culture. However, the incorporation of AFPs allowed survival similar to that of cells recovered from non-frozen embryos. Blastomere cryopreservation trials incorporating AFPI in the extender also demonstrated a significant increase in viability after freezing. Our findings demonstrated that delivery of AFPs into zebrafish embryos by incubation in media containing protein at early stages is a simple and harmless method that increases cryoprotection of the cellular compartment. This beneficial effect is also noticed in blastomeres, encouraging their use in further protocols for embryo cryopreservation.

Evaluation of oxidative DNA damage promoted by storage in sperm from sex-reversed rainbow trout.

Short-term storage and cryopreservation of sperm are two common procedures in aquaculture, used for routine practices in artificial insemination reproduction and gene banking, respectively. Nevertheless, both procedures cause injuries affecting sperm motility, viability, cell structure and DNA stability, which diminish reproductive success. DNA modification is considered extremely important, especially when sperm storage is carried out with gene banking purposes. DNA damage caused by sperm storage is not well characterized and previous studies have reported simple and double strand breaks that have been attributed to oxidative events promoted by the generation of free radicals during storage. The objective of this study was to reveal DNA fragmentation and to explore the presence of oxidized bases that could be produced by oxidative events during short-term storage and cryopreservation in sex-reversed rainbow trout (Oncorhynchus mykiss) spermatozoa. Sperm from six males was analyzed separately. Different aliquots of the samples were stored 2h (fresh) or 5 days at 4 degrees C or were cryopreserved. Then spermatozoa were analyzed using the Comet assay, as well as combining this method with digestion with two endonucleases from Escherichia coli (Endonuclease III, that cut in oxidized cytosines, and FPG, cutting in oxidized guanosines). Both storage procedures yielded DNA fragmentation, but only short-term storage oxidative events were clearly detected, showing that oxidative processes affect guanosines rather than cytosines. Cryopreservation increases DNA fragmentation but the presence of oxidized bases was not noticed, suggesting that mechanisms other than oxidative stress could be involved in DNA fragmentation promoted by freezing.

Cryobanking as tool for conservation of biodiversity: effect of brown trout sperm cryopreservation on the male genetic potential.

Sperm cryobanking could be a good alternative to breeding in captivity in order to preserve genetic diversity. Sperm from two well-characterized brown trout populations originating from two river basins in the Northwest of Spain (Esla and Duerna), both threatened by extinction, was cryopreserved. In order to determine whether a sperm cryobank is the best option for preserving genetic profiles, cell viability, chromatin fragmentation, fertility and genetic variability of the offspring obtained with fresh and frozen sperm, were analyzed. Sperm viability was not reduced by freezing (87.0+/-3.32% to 77.9+/-3.59% and 77.6+/-6.53% to 76.6+/-2.61% in fresh and frozen sperm from Esla and Duerna, respectively). The percentage of fragmented DNA increased after freezing in spermatozoa from Esla males (from 4.7+/-0.23% to 6.0+/-0.28%), but not those from Duerna males. After freezing/thawing, the percentage of eyed embryos drops from 66.8+/-6.77% to 16.1+/-3.46% and from 50+/-8.97% to 11.5+/-2.50% in the Esla and Duerna basins, respectively. This reduction indicates that many spermatozoa have lost their ability to contribute to embryo development and this loss is not related to either spermatozoa viability or the DNA integrity. Genotypic determination by microsatellite analysis showed that frozen/thawed sperm provided offspring with a similar genetic profile to unfrozen milt, demonstrating the accuracy of the cryopreservation procedure. Taking into account the prolificacy of this species, even a low rate of success of fry after cryopreservation, could provide enough individuals to recover stable populations without altering the genetic profiles of the preserved strains. Therefore, cryopreservation is considered a safe, simple and cheap technology for gene banking in the analyzed brown trout populations.