Sperm DNA Hypomethylation Proximal to Reproduction Pathway Genes in Maturing Elite Norwegian Red Bulls

Genomic selection in modern farming demands sufficient semen production in young bulls. Factors affecting semen quality and production capacity in young bulls are not well understood; DNA methylation, a complicated phenomenon in sperm cells, is one such factors. In this study, fresh and frozen-thawed semen samples from the same Norwegian Red (NR) bulls at both 14 and 17 months of age were examined for sperm chromatin integrity parameters, ATP content, viability, and motility. Furthermore, reduced representation bisulfite libraries constructed according to two protocols, the Ovation R RRBS Methyl-Seq System (Ovation method) and a previously optimized gel-free method and were sequenced to study the sperm DNA methylome in frozen-thawed semen samples. Sperm quality analyses indicated that sperm concentration, total motility and progressivity in fresh semen from 17 months old NR bulls were significantly higher compared to individuals at 14 months of age. The percentage of DNA fragmented sperm cells significantly decreased in both fresh and frozen-thawed semen samples in bulls with increasing age. Libraries from the Ovation method exhibited a greater percentage of read loss and shorter read size following trimming. Downstream analyses for reads obtained from the gel-free method revealed similar global sperm DNA methylation but differentially methylated regions (DMRs) between 14- and 17 months old NR bulls. The majority of identified DMRs were hypomethylated in 14 months old bulls. Most of the identified DMRs (69%) exhibited a less than 10% methylation difference while only 1.5% of DMRs exceeded a 25% methylation difference. Pathway analysis showed that genes annotated with DMRs having low methylation differences (less than 10%) and DMRs having between 10 and 25% methylation differences, could be associated with important hormonal signaling and sperm function relevant pathways, respectively. The current research shows that RRBS in parallel with routine sperm quality analyses could be informative in reproductive capacity of young NR bulls. Although global sperm DNA methylation levels in 14 and 17 months old NR bulls were similar, regions with low and varying levels of DNA methylation differences can be identified and linked with important sperm function and hormonal pathways.publishedVersio

Semen quality parameters including metabolites, sperm production traits and fertility in young Norwegian Red AI bulls

Genomic selection in cattle breeding has gradually allowed younger bulls to be recruited for semen production. In this study, sperm quality parameters, seminal plasma and sperm metabolites, semen production capacity and fertility in young Norwegian Red bulls were analysed. For in vitro analyses of sperm quality and metabolites, ejaculates were collected from the same 25 bulls at both 14 and 17 months of age. Semen production and fertility data were collected for all Norwegian Red bulls in production from December 2017 throughout 2019. Bull fertility was measured as 56 days non-return rate (NR56), for both age groups.acceptedVersionpublishedVersio

Semen quality parameters including metabolites, sperm production traits and fertility in young Norwegian Red AI bulls

Genomic selection in cattle breeding has gradually allowed younger bulls to be recruited for semen production. In this study, sperm quality parameters, seminal plasma and sperm metabolites, semen production capacity and fertility in young Norwegian Red bulls were analysed. For in vitro analyses of sperm quality and metabolites, ejaculates were collected from the same 25 bulls at both 14 and 17 months of age. Semen production and fertility data were collected for all Norwegian Red bulls in production from December 2017 throughout 2019. Bull fertility was measured as 56 days non-return rate (NR56), for both age groups. In both fresh and frozen-thawed semen samples, the proportion of hyperactive spermatozoa, average path velocity, curvilinear velocity and amplitude of lateral head displacement were higher in samples collected at 17 months of age compared to 14 months (PSemen quality parameters including metabolites, sperm production traits and fertility in young Norwegian Red AI bullsacceptedVersio

Sperm quality parameters, fertilizing potential, metabolites, and DNA methylation in cold-stored and cryopreserved milt from Atlantic salmon (Salmo salar L.)

Cold storage and freezing/thawing of milt may affect sperm functionality and the subsequent fertilization ability of milt. This study aimed to investigate sperm quality parameters and fertilization potential of Atlantic salmon milt, stored cold and subsequently cryopreserved, using different storage conditions. The objective was also to assess if analysis of milt metabolites and sperm DNA methylation signatures could be applicable to further elucidate sperm quality and fertilization following preservation. Milt samples were collected from eight mature Atlantic salmon males and stored for 4 days at 2°C and 8°C. Samples were taken on day one of storage at 2°C and on day four of storage at 2°C and 8°C. Storage for 4 days at 8°C is expected to be detrimental to sperm quality, and was included to create contrasts. Correspondingly, aliquots of cold-stored milt were prepared for cryopreservation, resulting in a total of six experimental conditions. Samples from all six experimental conditions were used in fertilization trials and analyzed for sperm viability, motility, ATP content, DNA fragmentation index, and High DNA stainability. In addition, milt samples from four of the males were analyzed for targeted metabolites and DNA methylation signatures by reduced representation bisulfite sequencing. The fertilization trials were performed using sperm:egg ratios of 75 × 103 and 500 × 103, respectively. Storage duration, temperature, and cryopreservation of cold-stored milt influenced several sperm quality parameters, metabolites, and DNA methylation signatures. The total motility, progressive motility, ATP, and velocity parameters were the sperm parameters with the strongest correlation to fertilization rates (p < 0.01). Several metabolites were correlated with fertility rates in both cold-stored and cryopreserved samples (p < 0.05). The fertilizing capacity of cold-stored milt was significantly reduced after 4 days of storage at 8°C, while corresponding cryopreserved milt showed reduced fertilization at both storage temperatures (2°C and 8°C) (p < 0.05). The results indicate that cryopreservation of milt stored for 1 day does not compromise either fertilization ability or DNA methylation signatures.publishedVersio

Reproductive potential and semen attributes in Norwegian Red bulls

With the introduction of genomic selection in cattle breeding, younger bulls without any fertility records have been recruited for semen production. Bull fertility has a major impact on the overall bovine reproductive efficiency. Thus, it is of interest to the cattle breeding industry to have laboratory tests that can predict the fertilization potential of a semen sample. This thesis aimed to study sperm quality traits as well as underlying factors affecting reproductive potential of Norwegian Red bulls. Our results indicated that young bulls are mature enough for their semen to fulfil successful fertilization. However, sperm motility parameters, metabolite contents and semen production efficiency differed between young bulls of 14 and 17 months of age. Even though sperm motility parameters were found to be associated with bull fertility, DFI was the only sperm quality trait with a significant contribution to the model predicting bull fertility. It was demonstrated that conventional sperm quality parameters only partly explain the variation in bull fertility, and that underlying factors affecting fertility might be elucidated by metabolomics and sperm DNA methylation analysis

Optimization of a sperm-oviduct binding assay mimicking in vivo conditions. Adoption of sperm separation methods and protocols for analysing sperm motility and intracellular Ca2+ level

English: An in vitro model that mimics the interactions between spermatozoa and oviductal epithelial cells can be used to increase the knowledge about the function of the oviduct and the formation of a sperm reservoir in vivo. The aim of the present study was to optimize methods for culturing bovine epithelial cells (BOECs) bi-dimensionally on plastic and three-dimensionally on polyester membrane. These cells were used in a sperm binding assay for evaluation of sperm-BOEC binding and release capacity. In order to measure multiple sperm attributes of the cells evaluated in the binding assay, adaption of protocols for evaluation of sperm motility parameters by CASA and intracellular Ca2+ level by flow cytometry analysis was performed. In addition, the effect of separating sperm cells by Percoll® and BoviPure® centrifugation was evaluated measuring sperm viability, acrosome integrity, motility, intracellular Ca2+ level, total ATP content and sperm-BOEC binding and release capacity. Findings demonstrated that 1·106 sperm cells/ml is an optimal sperm concentration for the BOEC binding and release assay, and epithelial cells from both ipsi- and contra-lateral oviducts can be used for culturing. BOECs cultured on collagen coated polyester membrane have a more in vivo like structure than BOECs cultured on plastic, allowing a more specific binding of sperm cells to the monolayers. In addition, our results showed that BoviPure® and Percoll® centrifugation improved the quality of the separated sperm population. However, the degree of improvement varied between the parameters analysed. BoviPure® and Percoll® centrifuged sperm cells had a higher binding capacity to in vitro cultured BOECs, with highest binding capacity for BoviPure®. These findings suggest that BoviPure® is an acceptable alternative to Percoll® for separating bull sperm and for use in the sperm-BOEC binding and release assay. However, both methods can be used to mitigate the sperm viability differences in the binding assay

Optimization of a sperm-oviduct binding assay mimicking in vivo conditions. Adoption of sperm separation methods and protocols for analysing sperm motility and intracellular Ca2+ level

Mastergradsoppgave i næringsrettet bioteknologi, Avdeling for lærerutdanning og naturvitenskap, Høgskolen i Hedmark, 2014. Master of applied and commercial biotechnology.English: An in vitro model that mimics the interactions between spermatozoa and oviductal epithelial cells can be used to increase the knowledge about the function of the oviduct and the formation of a sperm reservoir in vivo. The aim of the present study was to optimize methods for culturing bovine epithelial cells (BOECs) bi-dimensionally on plastic and three-dimensionally on polyester membrane. These cells were used in a sperm binding assay for evaluation of sperm-BOEC binding and release capacity. In order to measure multiple sperm attributes of the cells evaluated in the binding assay, adaption of protocols for evaluation of sperm motility parameters by CASA and intracellular Ca2+ level by flow cytometry analysis was performed. In addition, the effect of separating sperm cells by Percoll® and BoviPure® centrifugation was evaluated measuring sperm viability, acrosome integrity, motility, intracellular Ca2+ level, total ATP content and sperm-BOEC binding and release capacity. Findings demonstrated that 1·106 sperm cells/ml is an optimal sperm concentration for the BOEC binding and release assay, and epithelial cells from both ipsi- and contra-lateral oviducts can be used for culturing. BOECs cultured on collagen coated polyester membrane have a more in vivo like structure than BOECs cultured on plastic, allowing a more specific binding of sperm cells to the monolayers. In addition, our results showed that BoviPure® and Percoll® centrifugation improved the quality of the separated sperm population. However, the degree of improvement varied between the parameters analysed. BoviPure® and Percoll® centrifuged sperm cells had a higher binding capacity to in vitro cultured BOECs, with highest binding capacity for BoviPure®. These findings suggest that BoviPure® is an acceptable alternative to Percoll® for separating bull sperm and for use in the sperm-BOEC binding and release assay. However, both methods can be used to mitigate the sperm viability differences in the binding assay

Sperm chromatin integrity and DNA methylation in Norwegian Red bulls of contrasting fertility

In this study, the complexity of chromatin integrity was investigated in frozen-thawed semen samples from 37 sires with contrasting fertility, expressed as 56-day non-return rates (NR56). Protamine deficiency, thiols, and disulfide bonds were assessed and compared with previously published data for DNA fragmentation index (DFI) and high DNA stainability (HDS). In addition, in vitro embryo development and sperm DNA methylation were assessed using semen samples from 16 of these bulls. The percentages of DFI and HDS were negatively associated with NR56 and cleavage rate and positively associated with sperm protamine deficiency (p < 0.05). Significant differences in cleavage and blastocyst rates were observed between bulls of high and low NR56. However, once fertilization occurred, further development into blastocysts was not associated with NR56. The differential methylation analysis showed that spermatozoa from bulls of low NR56 were hypermethylated compared to bulls of high NR56. Pathway analysis showed that genes annotated to differentially methylated cytosines could participate in different biological pathways and have important biological roles related to bull fertility. In conclusion, sperm cells from Norwegian Red bulls of inferior fertility have less compact chromatin structure, higher levels of DNA damage, and are hypermethylated compared with bulls of superior fertility

Differences in sperm functionality and intracellular metabolites in Norwegian Red bulls of contrasting fertility

In the dairy breeding industry, prediction of bull fertility in artificial insemination (AI) is important for efficient and economically sustainable production. However, it is challenging to identify bulls with superior fertility applying conventional in vitro sperm assays. In the present study, sperm functionality was investigated to identify a multivariate model that could predict fertility. Two groups of young Norwegian Red bulls were selected, one with inferior fertility (18 bulls) and one with superior fertility (19 bulls) based on non-return rate after 56 days (NR56). Frozen-thawed semen doses were analysed for sperm chromatin integrity, viability, acrosome integrity, motility, and ATP content. A targeted approach was used to study intracellular concentrations of amino acids and trace elements in viable sperm cells. Significant differences between the two groups of bulls were observed, both for sperm functional attributes and intracellular concentrations of metabolites. Pearson correlation analyses indicated a negative relationship between NR56 and chromatin integrity parameters, DNA fragmentation index (DFI) and high DNA stainability (HDS). Several motility parameters correlated positively with NR56. The concentrations of cysteine and glutamic acid in sperm cells correlated negatively with NR56, while the concentrations of aspartic acid, leucine and serine showed a positive NR56-correlation. The sperm intracellular concentrations of the trace elements Fe, Al and Zn, correlated negatively with NR56. Correlations were observed between several sperm parameters and metabolites. Stepwise multiple regression analysis indicated that the best predictor of NR56 was a model containing %DFI, together with the intracellular sperm concentration of aspartic acid, Fe and Zn. This model explained 59% of the variability in NR56.publishedVersio

Sperm DNA Hypomethylation Proximal to Reproduction Pathway Genes in Maturing Elite Norwegian Red Bulls

Genomic selection in modern farming demands sufficient semen production in young bulls. Factors affecting semen quality and production capacity in young bulls are not well understood; DNA methylation, a complicated phenomenon in sperm cells, is one such factors. In this study, fresh and frozen-thawed semen samples from the same Norwegian Red (NR) bulls at both 14 and 17 months of age were examined for sperm chromatin integrity parameters, ATP content, viability, and motility. Furthermore, reduced representation bisulfite libraries constructed according to two protocols, the Ovation R RRBS Methyl-Seq System (Ovation method) and a previously optimized gel-free method and were sequenced to study the sperm DNA methylome in frozen-thawed semen samples. Sperm quality analyses indicated that sperm concentration, total motility and progressivity in fresh semen from 17 months old NR bulls were significantly higher compared to individuals at 14 months of age. The percentage of DNA fragmented sperm cells significantly decreased in both fresh and frozen-thawed semen samples in bulls with increasing age. Libraries from the Ovation method exhibited a greater percentage of read loss and shorter read size following trimming. Downstream analyses for reads obtained from the gel-free method revealed similar global sperm DNA methylation but differentially methylated regions (DMRs) between 14- and 17 months old NR bulls. The majority of identified DMRs were hypomethylated in 14 months old bulls. Most of the identified DMRs (69%) exhibited a less than 10% methylation difference while only 1.5% of DMRs exceeded a 25% methylation difference. Pathway analysis showed that genes annotated with DMRs having low methylation differences (less than 10%) and DMRs having between 10 and 25% methylation differences, could be associated with important hormonal signaling and sperm function relevant pathways, respectively. The current research shows that RRBS in parallel with routine sperm quality analyses could be informative in reproductive capacity of young NR bulls. Although global sperm DNA methylation levels in 14 and 17 months old NR bulls were similar, regions with low and varying levels of DNA methylation differences can be identified and linked with important sperm function and hormonal pathways