Mammalian sperm capacitation: In vivo and in vitro juxtaposition

The development of assisted reproductive technologies (ART) in mammalian species such as in vitro embryo production (IVEP) has the potential to provide great benefits for significant population increase, improve genetic performance and advancement, and reduce transmission of venereal diseases. Correspondingly, in vitro capacitation of sperm is also paramount, related to the ability of sperm to fertilize oocytes, and was created to imitate in vivo conditions in the female reproductive tract. Amid in vitro capacitation developments, studies on how far in vitro capacitation has progressed in mimicking in vivo scenes have not been thoroughly reviewed as a comparative form. Therefore, the present study outlined the series of alterations in mammalian sperm capacitation during their journey in the female reproductive tract by exploring and juxtaposing processes under in vivo and in vitro conditions. Several essential aspects that become gaps between in vivo and in vitro were also identified and elaborated comprehensively in this systematic literature review. We noted that although in vitro capacitation procedures in certain mammalian species have made promising progress and improvements, it is still poorly successful in other species like horses. Our findings further postulated that the occurrence of cryocapacitation, the high ratio of capacitated sperm/oocyte required for successful fertilization, and the incidence of polyspermy cause capacitation under in vitro settings is less efficient and not yet fully comparable to in vivo. This work is therefore proposed several aspects that need to be bettered from in vitro milieu to make it analogous to in vivo environments in modulating sperm capacitation.