The Behavior and Acrosomal Status of Mouse Spermatozoa In Vitro, and Within the Oviduct During Fertilization after Natural Mating

Abstract

Although 90%-100% of mouse oocytes can be fertilized in vitro with capacitated spermatozoa within 1 h after insemination, oocytes within the oviduct are fertilized one by one over a period of several hours. In vitro experiments showed that both acrosome-intact and acrosome-reacted spermatozoa entered the cumulus oophorus, but that acrosome-reacted spermatozoa reached the surface of oocytes more readily than acrosome-intact spermatozoa. During the period of fertilization within the oviduct, acrosome-reacted spermatozoa were seen throughout the isthmus, but with higher incidence in the upper than in the mid- and lower segments of the isthmus. Very few spermatozoa were present in the ampulla, and almost all were acrosome reacted. Although the cumulus oophorus and zona pellucida are known to be able to induce or facilitate the acrosome reaction of spermatozoa, this picture makes it likely that almost all fertilizing mouse spermatozoa within the oviduct begin to react before ascending from the isthmus to the ampulla. We witnessed a reacted spermatozoon that stayed on the zona pellucida of a fertilized oocyte for a while; it then moved out of the cumulus before reaching the zona pellucida of the nearby unfertilized oocyte. We noted that only a few spermatozoa migrate from the isthmus to the ampulla during the progression of fertilization, and this must be one of the reasons why we do not see many spermatozoa swarming around a single oocyte during in vivo fertilization.

Natriuretic peptide type C induces sperm attraction for fertilization in mouse

“…The number of spermatozoa with NPR2-positive staining was further increased after treatment with NPPC, suggesting that only the spermatozoa with functional NPR2 are attracted by NPPC. This is consistent with recent studies that only a few spermatozoa migrate from the isthmus to the ampulla during the progression of fertilization616263. Thus, the capacitated spermatozoa show attraction by exposing the functional receptor NPR2, and travel from the isthmus of the oviduct to the ampulla during ovulation.…”

An intact acrosome is required for the chemotactic response to progesterone in mouse spermatozoa

“…For many years, the acrosome reaction was postulated to occur upon sperm interaction with the zona pellucida of ovulated eggs (Buffone, Hirohashi, & Gerton, ; Hirohashi, ). Yet, recent studies reported that acrosomal exocytosis is triggered before reaching the ampulla, where fertilization occurs in the mouse (Hino et al, ; Muro et al, ; Spina et al, ). Our current study suggests that spermatozoa require an intact acrosome to sense a chemical guidance cue, leading to the hypotheses that chemotaxis precedes acrosomal exocytosis and that both processes sequentially occur en route to the egg.…”

“…Spermatozoa must exocytose its acrosome in order to bind to and fuse with the egg plasma membrane (Cuasnicú, Da Ros, Weigel Muñoz, & Cohen, ). Most fertilizing mouse spermatozoa complete this acrosome reaction before reaching the zona pellucida (Jin et al, ), probably while travelling through the upper isthmus (Hino et al, ; Muro et al, ; Spina et al, ). Therefore, an intriguing question is whether or not the responsiveness to a chemoattractant can change depending on acrosome's integrity.…”

Changes in the Cellular Distribution of Tyrosine Phosphorylation and Its Relationship with the Acrosomal Exocytosis and Plasma Membrane Integrity during In Vitro Capacitation of Frozen/Thawed Bull Spermatozoa

“…The release of these hydrolytic enzymes is thought to facilitate the sperm penetration of the cumulus oocyte complex [29]. However, recent publications have shown that mouse spermatozoa that reach the fertilization site have already undergone AE [30] and the same seems to occur in cattle [31][32][33]. The AE is a calcium-dependent exocytotic event [28] that can be artificially induced using calcium ionophores, such as ionomycin and A23187, and also with physiological molecules, such as progesterone or glycoproteins from the zona pellucida of some species [34,35].…”