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Relationship between sperm capacitation and fertility in cryopreserved semen of Nellore bulls: emphasis on sperm microRNA profile and metabolomics


The fertility potential of cryopreserved semen from bulls has been intensely studied, even so, there is still no understanding of all the processes that are involved in the success of fertilization, among which the sperm capacitation stands out. Due to the high condensation of DNA, spermatozoa are inert to transcription and translation processes and depend on transcripts acquired during spermatogenesis and post-testicular transit. In this sense, post-transcriptional role of RNA is crucial, being able to regulate the translations of proteins. Among these, include miRNAs, which can be potential regulators of fertility and can be used as biomarkers, with effective functions in the processes that spermatozoa go through until they fertilize the oocyte, including sperm capacitation, and embryo development. In addition, the molecular events of sperm capacitation include amino acids (proteins), lipids, carbohydrates, nucleic acids and other organic and inorganic molecules, which can be evaluated through metabolomics, capable of evaluating and determining the profile of these small molecules. To understand the relationship between sperm capacitation and fertility in cryopreserved bovine semen, with emphasis on miRNA profiles and sperm metabolomics, this research project will be divided into three studies. In the first study, fresh and cryopreserved semen samples from 12 Nellore bulls will be evaluated for sperm capacitation events, differentiating those effects caused during the semen cryopreservation process; from these techniques the samples will be classified according to the responsiveness to in vitro sperm capacitation. In the second study, bulls with greater and lesser responsiveness to sperm capacitation in vitro (evaluated using the techniques in the first study), will be used and will be compared in terms of miRNA and metabolic profiles, in the search for biomarkers related to sperm capacitation events. In the third study batches of cryopreserved commercial semen of known fertility will be evaluated for sperm capacitation events, using the techniques from the first study, and for metabolic and miRNA profiles (defined in the second study). With the results of this study, it is intended to better elucidate the sperm mechanisms that can negatively interfere with semen fertility and contribute to the diagnosis of fertility failure of batches of cryopreserved semen before being used in FTAI programs, avoiding obtaining of low pregnancy rates, thus generating greater reproductive efficiency, enabling an increase in cattle productivity for Brazil and the world. (AU)

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