Abstract
Simple SummaryUnderstanding how gamete chromatin influences fertilization is highly important not only to improve animal production, but also to develop new biomarkers helping in the selection of those animals with higher fertility potential. In this regard, sperm telomere length has been pointed out as a putative biomarker in human infertility, but no studies have been conducted into its influence in pig fertility. Here, we determined that sperm telomere length is independent from the conventional sperm quality parameters and, through the production of in vitro embryos, we showed that it is indicative of the percentage of morulae and blastocysts, thus becoming useful to be used as biomarker in this species.Telomere length has attracted much interest as a topic of study in human reproduction; furthermore, the link between sperm telomere length and fertility outcomes has been investigated in other species. This biomarker, however, has not been much explored in other animals, such as pigs, and whether it is related to sperm quality and fertility outcomes remains unknown. The present work aimed to determine the absolute value of telomere length in pig sperm, as well as its relationship to sperm quality parameters and embryo development. Telomere length was determined through quantitative fluorescence in situ hybridization (qFISH) in 23 pig sperm samples and data were correlated to quality parameters (motility, morphology, and viability) and in vitro fertilization outcomes. We found that the mean telomere length in pig sperm was 22.1 ± 3.6 kb, which is longer than that previously described in humans. Whilst telomere length was not observed to be correlated to sperm quality variables (p > 0.05), a significant correlation between telomere length and the percentage of morulae 6 days after in vitro fertilization was observed (rs = 0.559; 95% C.I. = (−0.007 to 0.854); p = 0.047). Interestingly, this correlation was not found when percentages of early blastocysts/blastocysts (rs = 0.410; 95% C.I. = (−0.200 to 0.791); p = 0.164) and of hatching/hatched blastocysts (rs = 0.356; 95% C.I. = (− 0.260 to 0.766); p = 0.233) were considered. Through the separation of the samples into two groups by the median value, statistically significant differences between samples with shorter telomeres than the median and samples with longer telomeres than the median were found regarding development to morula (11.5 ± 3.6 vs. 21.8 ± 6.9, respectively) and to early blastocyst/blastocysts (7.6 ± 1.4 vs. 17.9 ± 12.2, respectively) (p < 0.05). In the light of these results, sperm telomere length may be a useful biomarker for embryo development in pigs, as sperm with longer telomeres lead to higher rates of morulae and blastocysts.
Highlights
Telomeres, ribonucleoprotein structures located at the end of chromosomes, are involved in the maintenance of genomic integrity and stability and are crucial for gamete generation [1]
In the light of all the aforementioned, the aims of the present study were: (a) to characterize telomere length in pig sperm through the adaptation of an improved method based on quantitative fluorescence in situ hybridization, and (b) to evaluate the relationship of that sperm telomere length with semen quality, in vitro fertilization (IVF) outcomes and embryo development
Thereafter, and in order to determine the relationship between fluorescence intensity and fluorochrome molecules, the analysis of fluorescent spheres led to a linear correlation between these two variables (r = 0.997; p = 0.045; n = 36) which, in turn, could be extrapolated to absolute telomere length in our hybridization system
Summary
Ribonucleoprotein structures located at the end of chromosomes, are involved in the maintenance of genomic integrity and stability and are crucial for gamete generation [1]. Telomere sequences, which are similar in all vertebrates, are composed of repetitive, non-coding, double-stranded sequences of thousands of hexanucleotide DNA repeats (TTAGGG)n coupled to specialized proteins of the shelterin complex and noncoding RNAs. Telomeres prevent the chromosome ends to be erroneously recognized as double-strand breaks [2]. Despite the conserved sequence of telomeres among mammals, the number of repetitions may be highly variable, the different tissues and cells from the same individual having distinct telomere lengths [3]. Factors such as age, sex or exposure to oxidative stress and genotoxic agents including radiation and chemical agents have been purported to influence that length, leading to telomere attrition [4]. As telomeres consist of G-rich sequences, they could show higher susceptibility to oxidative radicals and be more sensitive to the accumulation of 8-oxoG, underlying the disruption of telomeric proteins and the inhibition of telomerase, which results, in turn, in the shortening, dysfunction, and instability of telomeres [6]
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