Review: The epic journey of sperm through the female reproductive tract

Abstract

Millions or billions of sperm are deposited by artificial insemination or natural mating into the cow reproductive tract but only a few arrive at the site of fertilization and only one fertilizes an oocyte. The remarkable journey that successful sperm take to reach an oocyte is long and tortuous, and includes movement through viscous fluid, avoiding dead ends and hostile immune cells. The privileged collection of sperm that complete this journey must pass selection steps in the vagina, cervix, uterus, utero-tubal junction and oviduct. In many locations in the female reproductive tract, sperm interact with the epithelium and the luminal fluid, which can affect sperm motility and function. Sperm must also be tolerated by the immune system of the female for an adequate time to allow fertilization to occur. This review emphasizes literature about cattle but also includes work in other species that emphasizes critical broad concepts. Although all parts of the female reproductive tract are reviewed, particular attention is given to the sperm destination, the oviduct.

Keywords: bovine; cervix; oviduct; sperm; uterus.

Figure 1.

Structures of glycans that bind bovine (Le^A) and porcine sperm (bi-SiaLN, bi-LN, and Le^X), and the related glycan that does not (LN). Le^A is found on the bovine oviduct epithelium. bi-SiaLN is abundant on the epithelium of the porcine ampulla and isthmus including ciliated and non-ciliated cells. Le^X is found in the porcine isthmus but not the ampulla.

Figure 2.

Sperm bind to oviduct cell aggregates isolated from the isthmus (A, porcine sperm) and beads to which Le^A trisaccharide has been attached (B, bovine sperm).