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      Bovine Sperm Sexing Alters Sperm Morphokinetics and Subsequent Early Embryonic Development

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          Abstract

          In artificial insemination the use of sex-sorted bovine sperm results in reduced conception, the causes of which are only partly understood. Therefore, we set out to investigate the effects of sexing on bovine sperm function and early embryonic development. Computer-assisted semen analysis (CASA) of sperm of the same bulls (n = 5), before and after sexing, demonstrated significantly reduced fast (A) and slow (B) progressively motile sperm (p < 0.05) after sexing. Sexed-sperm also revealed significantly less hyperactivated sperm (p < 0.05). As shown by time-lapse videomicroscopy of in vitro produced embryos (n = 360), embryos derived from sexed-sperm displayed significantly increased incidences of arrest at the 4-cell stage (p < 0.05). The relative risk for shrinkage/fusion of blastomeres with subsequent lysis was 1.71 times higher in the embryos derived from sexed-sperm as compared to conventional embryos (p < 0.05) resulting in significantly reduced blastocyst rates (p < 0.001). The relative risk for cleavage was 2.36 times lower in the embryos derived from sex-sorted sperm (p < 0.001). Additionally, sexed-sperm-derived embryos showed reduced survival times (hazard ratio HR = 1.54, p < 0.001) which were bull dependent (p < 0.001). However, the percentage of apoptotic cells was similar to conventional embryos. Furthermore, embryos derived from sexed-sperm were found to reach developmental stages at similar timings as conventional embryos. Our results suggest that reduced conception rates after sexing are due to altered sperm morphokinetics, decreasing the chance of sperm to reach and fertilise the oocyte, and aberrant early embryonic development.

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          Control of hyperactivation in sperm.

          Sperm hyperactivation is critical to fertilization, because it is required for penetration of the zona pellucida. Hyperactivation may also facilitate release of sperm from the oviductal storage reservoir and may propel sperm through mucus in the oviductal lumen and the matrix of the cumulus oophorus. Hyperactivation is characterized by high amplitude, asymmetrical flagellar bending. This is a review of the original literature on the mechanisms that regulate hyperactivation, including physiological factors and signaling pathways. Computer-assisted semen analysis systems can be used to identify hyperactivated sperm by setting minimum thresholds for curvilinear velocity (VSL) and lateral head movement and a maximum threshold for path linearity. Hyperactivation is triggered by a rise in flagellar Ca(2+) resulting from influx primarily through plasma membrane CatSper channels and possibly also by release of Ca(2+) from a store in the redundant nuclear envelope. It requires increased pH and ATP production. The physiological signals that trigger the rise in Ca(2+) remain elusive, but there is evidence that the increased Ca(2+) acts through a calmodulin/calmodulin kinase pathway. Hyperactivation is considered part of the capacitation process; however, the regulatory pathway that triggers hyperactivation can operate independently from that which prepares sperm to undergo the acrosome reaction. Hyperactivation may be modulated by chemotactic signals to turn sperm toward the oocyte. Little is known about exactly what triggers hyperactivation in human sperm. This information could enable clinicians to develop reliable fertility assays to assess normal hyperactivation in human sperm samples.
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            Regulation of sperm storage and movement in the mammalian oviduct.

            The oviduct plays a vital role in ensuring successful fertilization and normal early embryonic development. The male inseminates many thousands or even millions of sperm, but this alone does not ensure that fertilization will be successful. The female tract, particularly the oviduct, provides filters that select for normal vigorously motile sperm. In conjunction with molecules in the seminal plasma and on sperm, the female tract regulates how and when sperm pass though the tract to reach the site of fertilization. Various regulatory processes control sperm passage into and through the oviduct. In some species, the uterotubal junction opens and closes to regulate when sperm may enter; furthermore, passage through the junction requires certain proteins on the sperm surface. Most of the sperm that manage to enter the oviduct soon become trapped and held in a reservoir. In marsupials and insectivores, this involves trapping sperm in mucosal crypts; while in most other mammalian species, this involves binding sperm to the oviductal epithelium. As the time of ovulation approaches, the sperm in the reservoir undergo capacitation, including motility hyperactivation. Capacitating sperm shed proteins that bind them to the mucosal epithelium, while hyperactivation assists the sperm in pulling off of the epithelium and escaping out of mucosal pockets. The process of sperm release is gradual, reducing chances of polyspermic fertilization. Released sperm may be guided towards the oocyte by secretions of the oviduct, cumulus cells, or oocyte. Hyperactivation likely assists sperm in penetrating the cumulus matrix and is absolutely required for penetrating the oocyte zona pellucida and achieving fertilization.
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              Hyperactivation of mammalian spermatozoa: function and regulation.

              Hyperactivation is a movement pattern observed in spermatozoa at the site and time of fertilization in mammals. It may be critical to the success of fertilization, because it enhances the ability of spermatozoa to detach from the wall of the oviduct, to move around in the labyrinthine lumen of the oviduct, to penetrate mucous substances and, finally, to penetrate the zona pellucida of the oocyte. The movement of hyperactivated spermatozoa appears different under different physical conditions and in different species, but basically it involves an increase in flagellar bend amplitude and beat asymmetry. Presumably, there is a signal or signals in the oviduct to initiate hyperactivation at the appropriate time; however, none has yet been identified. There is evidence that the source of the signal is follicular fluid, yet spermatozoa are known to hyperactivate before ovulation would release the fluid into the oviduct. Although the signal transduction cascade regulating hyperactivation remains to be described completely, it is clear that calcium ions interact with the axoneme of the flagellum to switch on hyperactivation. The process may also involve increases in intracellular cAMP, which at least is required to support motility in general. Although hyperactivation usually occurs during capacitation, the two events are regulated by different pathways.
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                Author and article information

                Contributors
                sabine.koelle@ucd.ie
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                10 April 2020
                10 April 2020
                2020
                : 10
                : 6255
                Affiliations
                [1 ]ISNI 0000 0001 0768 2743, GRID grid.7886.1, School of Medicine, Health Sciences Centre, University College Dublin, ; Dublin, Ireland
                [2 ]ISNI 0000 0004 1936 8868, GRID grid.4563.4, School of Medicine, University of Nottingham, ; Nottingham, United Kingdom
                [3 ]ISNI 0000 0004 1936 973X, GRID grid.5252.0, School of Veterinary Medicine, Institute of Veterinary Anatomy, Histology and Embryology, University of Munich, ; Munich, Germany
                Article
                63077
                10.1038/s41598-020-63077-6
                7148378
                32277124
                a8fb29fe-9e21-41e9-a907-5069bc76660f
                © The Author(s) 2020

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 27 October 2019
                : 20 March 2020
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                © The Author(s) 2020

                Uncategorized
                embryogenesis,embryology
                Uncategorized
                embryogenesis, embryology

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