Sperm Interactions from Insemination to Fertilization

Abstract

The task of spermatozoa is to transport its DNA-load as efficiently and safely as possible from the male organism to the female. Before it reaches its destination, it has to pass almost through the entire female reproductive tract, a potentially hostile environment. During passage, it is confronted by a sophisticated system that provides sperm storage sides but also possibly facilitates selection. The present review attempts to summarize the current knowledge of sperm interactions during that journey. A better understanding of the highly complex processes taking place between insemination and fertilization will be necessary to improve the efficiency of conventional reproductive techniques as well as for enabling the development and establishment of new ones.

Sperm selection in the female mammalian reproductive tract. Focus on the oviduct: Hypotheses, mechanisms, and new opportunities

“…Immunologic studies of sperm transport have also shown that once a cohort of spermatozoa reaches the uterus, they induce the "postmating inflammatory response." This involves an influx of neutrophils into the uterine lumen [86,87] which, in the pig at least, selectively reject or permit the further progress of the spermatozoa. The major histocompatibility system (MHC) has been widely researched for its relevance to reproduction, and it is likely that mechanisms exist to identify and select the best match between maternal and paternal MHC characteristics [88,89].…”

Storage and Release of Spermatozoa from the Pre-Uterine Tube Reservoir

“…Low numbers of spermatozoa appear to continually detach from uterine tube epithelium [4]–[6], but overall the attachment of spermatozoa slows the process of capacitation so that the fertile life of spermatozoa is maintained until close to ovulation when they become activated and increasing numbers detach with hyperactive motility [5], [34], [35]. It is not clear how the numbers of spermatozoa within the uterine tube reservoir are maintained particularly when the interval from mating to ovulation is prolonged, although it has been suggested that the uterus provides a store of spermatozoa for the uterine tube [11], [36], [37]; details of how this might be achieved have not previously been described.…”

“…Our findings, that the uterine sperm reservoir is affected by peri-ovulatory signals in a similar way to the uterine tube reservoir add to the current literature. Further investigations are needed into the mechanisms associated with detachment of spermatozoa, since although changes in motility characteristics of spermatozoa are likely to be important to facilitate detachment, at least for the uterine tube, a variety of interesting biological mechanism have now been detected [36], [41], [42]. In the present study we were able to demonstrate that both follicular fluid and solubilised zona pellucida in the presence of capacitating conditions induced capacitation but not greater than CCM alone, but resulted in a greater proportion of detached spermatozoa exhibiting hyperactive motility than observed in capacitating conditions alone, adding weight to the evidence proposing that detachment of spermatozoa is regulated by peri-ovulatory events.…”

Practical implications of sperm selection techniques for improving reproduction

“…An important consideration for IVF or ICSI is that the selection of normal spermatozoa that occurs in the female reproductive tract is not present (Suarez, 2007) potentially allowing abnormal spermatozoa or those with damaged chromatin to fertilize the oocyte (Rath et al, 2008). Although the oocyte is fertilized and activated, there may be problems due to the damaged chromatin during embryo development or even after implantation (Katari et al, 2009;Evenson, 2016).…”