At coitus, human sperm are deposited into the anterior vagina, where, to avoid vaginal acid and immune responses, they quickly contact cervical mucus and enter the cervix. Cervical mucus filters out sperm with poor morphology and motility and as such only a minority of ejaculated sperm actually enter the cervix. In the uterus, muscular contractions may enhance passage of sperm through the uterine cavity. A few thousand sperm swim through the uterotubal junctions to reach the Fallopian tubes (uterine tubes, oviducts) where sperm are stored in a reservoir, or at least maintained in a fertile state, by interacting with endosalpingeal (oviductal) epithelium. As the time of ovulation approaches, sperm become capacitated and hyperactivated, which enables them to proceed towards the tubal ampulla. Sperm may be guided to the oocyte by a combination of thermotaxis and chemotaxis. Motility hyperactivation assists sperm in penetrating mucus in the tubes and the cumulus oophorus and zona pellucida of the oocyte, so that they may finally fuse with the oocyte plasma membrane. Knowledge of the biology of sperm transport can inspire improvements in artificial insemination, IVF, the diagnosis of infertility and the development of contraceptives.

/pdf/sperm-transport-in-the-female-reproductive-tract-1wd76o2ooi.pdf

Sperm transport in the female reproductive tract

Contrary to the prevalent view, there seems to be no competition in the mammalian female genital tract among large numbers of sperm cells that are racing towards the egg. Instead, small numbers of the ejaculated sperm cells enter the Fallopian tube, and these few must be guided to make the remaining long, obstructed way to the egg. Here, we review the mechanisms by which mammalian sperm cells are guided to the egg.

https://www.royanaward.com/files13/Royan%20Award%20-%20Giojalas%20-%20pdf%20paper%201.pdf

Sperm guidance in mammals - an unpaved road to the egg.

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

/pdf/hyperactivation-of-mammalian-spermatozoa-function-and-3eah9ns7xm.pdf

Hyperactivation of mammalian spermatozoa: function and regulation

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.

/pdf/regulation-of-sperm-storage-and-movement-in-the-mammalian-22n4yoe7ua.pdf

Regulation of sperm storage and movement in the mammalian oviduct.

The identification of human sperm hyperactivated motility has potential importance in sperm function tests, as well as in quality control assays and in reproductive toxicology investigations. However, relatively little is known about this phenomenon and the variety of definitions used for hyperactivation has led to a great deal of confusion as to its occurrence and physiological relevance. This presentation is a critical review of a number of aspects of hyperactivated motility, including its identification and potential role(s) in mammalian fertilization. The initial sections of the review consider the mechanisms involved in the development and maintenance of mammalian sperm motility, and the structural and functional changes in spermatozoa which occur during transport through the female reproductive tract. The methods available for the quantification of aspects of sperm movement are also discussed, with an historical overview of sperm movement analysis.

/pdf/a-critical-review-of-the-physiological-importance-and-24713rvrib.pdf

A critical review of the physiological importance and analysis of sperm movement in mammals

Human spermatozoa accumulate in vitro in diluted follicular fluids obtained from follicles from which the eggs have been fertilized. Using capillary assays under a variety of experimental conditions (ascending or descending gradients of follicular fluid, or no gradient at all) and microscopic assays in which individual spermatozoa could be followed, we found that the sperm accumulation in follicular fluid was the result of both sperm chemotaxis and chemokinesis and eventually hyperactivation-like motility. We determined the optimal conditions for sperm accumulation, which involved sperm preincubation (possibly to induce sperm capacitation) and proper dilution of follicular fluid. In all the assays, the net accumulation was low, probably reflecting the chemotactic responsiveness of only a small fraction of the sperm population at any given time. We partially fractionated follicular fluid in a Centricon microconcentrator (Amicon, Danvers, MA) and by acetone precipitation, and found that at least one of the chemotactic factors is a small (< 10-kDa) molecule that is probably nonhydrophobic. This is the first time that sperm chemotaxis and chemokinesis in response to a follicular factor(s) in mammals has been established and has been distinguished from other processes that might cause sperm accumulation. The physiological significance of these findings is discussed.

/pdf/chemotaxis-and-chemokinesis-of-human-spermatozoa-to-48hwiqrif5.pdf

M. Manor

Papers

Chemotaxis and chemokinesis of human spermatozoa to follicular factors.

Atrial natriuretic peptide attracts human spermatozoa in vitro