Acrosome reaction of fowl sperm: Evidence for shedding of the acrosomal cap in intact form to release acrosomal enzyme

Abstract

The aim of this study was to determine the site of enzyme release from the acrosome and the fate of the acrosomal cap during the process of acrosome reaction (AR) in fowl sperm. Gelatin substrate coverslips with halos were subjected to scanning electron microscopy to determine the site from which acrosomal proteolytic enzyme was released to form a halo around the acrosome of individual sperm. Aliquots of sperm treated with solubilized inner perivitelline layer (IPL) containing 5 mmol CaCl(2) were simultaneously subjected to fluorescent staining with fluorescein isothiocyanate-labeled peanut agglutinin and scanning electron microscopy to evaluate AR of sperm and to examine the status of the acrosomal region, respectively. Inside the halos, a gelatin-free (proteolyzed gelatin) layer was found extending some distance around the acrosome of sperm. All of the sperm showing the formation of halos on gelatin had a single circular opening around their subacrosomal rod at the base of the acrosomal cap. Interaction of sperm with solubilized IPL in the presence of 5 mmol CaCl(2) resulted in 41.4 ± 1.8% of the sperm to undergo AR, as evaluated by fluorescein isothiocyanate-labeled peanut agglutinin. Similarly, as observed using scanning electron microscopy, 38.2 ± 2.3% of the sperm treated with solubilized IPL plus 5 mmol CaCl(2) had exposed subacrosomal rod. In all sperm examined, no sign of disruption of the acrosomal membrane was found in the apical region of the acrosome. Rather, the acrosomal caps were found intact detached from the acrosomal region of the sperm, indicating that AR of fowl sperm resulted in the intact removal of the acrosomal cap. Based on these experimental observations, we suggest that the process of AR in fowl sperm is unique; the release of the acrosomal proteolytic enzyme may occur through a single circular opening formed at the base of the acrosomal cap and the acrosomal cap is detached in intact form from the posterior acrosomal region of the sperm.

Peanut agglutinin specifically binds to a sperm region between the nucleus and mitochondria in tunicates and sea urchins

“…In vertebrates, detection of PNA in the region between the nucleus and midpiece has never been reported (refer to Figure g). PNA has also been reported to bind to the acrosomal region in birds (Ahammad et al, ; Okumura et al, ; Singh et al, ) and amphibians (Takamune, ).…”

Organization of Membrane Rafts in Chicken Sperm

“…In murine sperm, membrane rafts play important roles in acrosome exocytosis by stimulating membrane fusion between the APM and outer acrosomal membrane (Asano et al, 2013). However, acrosome exocytosis in chicken sperm appears to be induced without membrane fusion via the shedding of the acrosome cap in its intact form (Ahammad et al, 2013). Considering that membrane rafts regulate membrane fusion in diverse cell types (Salaun, et al, 2004), this difference in the machinery of acrosome exocytosis between mammalian and avian sperm might be attributable to distinctions in the functional roles of membrane rafts in sperm.…”

Molecular characterization and sub-cellular distribution of JNK and JIP4 protein kinases in spermatogenesis and acrosome reaction of the Chinese mitten crab Eriocheir sinensis H. Milne Edwards, 1853 (Crustacea: Brachyura: Varunidae)

“…In general, the AR is characterized by the fusion of the outer acrosomal with the plasma membrane of the sperm, followed by vesiculation of these membranes and enzyme release from the acrosomal matrix (Okamura and Nishiyama, 1978). The release of the acrosomal proteolytic enzyme has been demonstrated to occur through a single circular opening formed at the base of the acrosomal cap in fowl (Ahammad et al, 2013). As calcium can induce the AR, the calcium ionophore A23187 was used in this study to induce the AR as described by Zhu et al (2014) and Sun et al (2015).…”