Progress of sperm IZUMO1 relocation during spontaneous acrosome reaction

Abstract

It has been recently shown in mice that sperm undergo acrosome reaction (AR) by passing through cumulus cells; furthermore, the acrosome-reacted sperm can bind to zona pellucida and consequently fertilise the egg. During AR, the relocation of the primary fusion protein IZUMO1 into the equatorial segment is crucial for sperm-egg fusion. There is a high rate of spontaneous AR in rodents, with up to 60% in promiscuous species. The aim of this study was to clarify whether the IZUMO1 relocation in sperm after spontaneous and induced AR is the same, and whether there is a correlation between the speed of IZUMO1 relocation and species-specific mating behaviour in field mice. Immunofluorescent detection of IZUMO1 dynamics during the in vitro capacitation, spontaneous, calcium ionophore and progesterone-induced AR was monitored. Our results show that during spontaneous AR, there is a clear IZUMO1 relocation from the acrosomal cap to the equatorial segment, and further over the whole sperm head. In addition, there is positive tail tyrosine phosphorylation (TyrP) associated with hyperactive motility. Moreover, the beginning and the progress of IZUMO1 relocation and tail TyrP positively correlate with the level of promiscuity and the acrosome instability in promiscuous species. The findings that crucial molecular changes essential for sperm-egg fusion represented by dynamic movements of IZUMO1 also happen during spontaneous AR are vital for understanding fertilisation in mice.

Endoplasmic Reticulum Stress and Homeostasis in Reproductive Physiology and Pathology

“…Human spermatozoa that have completed capacitation bind to the zona pellucida and release the acrosome content (acrosome exocytosis). On the other hand, acrosome reaction occurs spontaneously [111,112]. Penetration of the zona pellucida by spermatozoa follows perivitelline entry, and is then finalized by binding and fusion to the oocyte plasma membrane [100].…”

Sperm-Egg Fusion: A Molecular Enigma of Mammalian Reproduction

“…It is followed by the acrosome reaction—fusion of the plasma and outer acrosome membranes, exposing the inner acrosome membrane and releasing the acrosomal content. It can be triggered by multiple factors—contact with ZP ( zona pellucida ), progesterone concentration or even spontaneously—suggesting that timing of this essential process is redundant and the different time of onset in different population of sperm may play a role in sperm competition [20]. The exact combination of causes and effects is not clear, however, it is well known that the acrosome reacted sperm penetrates the ZP, enters the perivitelline space and is able of fuse with the oolema [21].…”

Effects of latrunculin A on the relocation of sperm IZUMO1 during gamete interaction in mouse

“…IZUMO1 is initially located at the acrosomal cap region of both outer and inner acrosomal membrane in acrosome‐intact sperm (Satouh et al, ). Following acrosome exocytosis, IZUMO1 is redistributed to the equatorial segment or along the entire head of sperm; this process is referred to as “IZUMO1 relocation” (Miranda et al, ; Satouh et al, ; Sebkova, Ded, Vesela, & Dvorakova‐Hortova, ). This relocation process is essential for gamete fusion, as demonstrated by the inability of IZUMO1 to relocate in Tssk6 ‐null sperm (Sosnik et al, ).…”

“…head of sperm; this process is referred to as "IZUMO1 relocation" Satouh et al, 2012;Sebkova, Ded, Vesela, & Dvorakova-Hortova, 2013). This relocation process is essential for gamete fusion, as demonstrated by the inability of IZUMO1 to relocate in Tssk6-null sperm .…”