Sperm plasma membrane

About: Sperm plasma membrane is a research topic. Over the lifetime, 1016 publications have been published within this topic receiving 49964 citations.

Mammalian Sperm Acrosome Reaction: Where Does It Begin Before Fertilization?

Abstract: Spermatozoa of many animal species, including humans, must undergo a Ca þ -dependent exocytotic process known as the acrosome reaction (AR) before fertilizing oocytes. The AR, first described in the sea urchin and starfish by Dan [1, 2], involves multiple fusions of the outer acrosomal membrane with the overlying sperm plasma membrane. This allows release of the contents of the acrosome to the outside of the sperm cell. Lytic acrosomal materials digest or dissociate the oocyte’s glycoprotein coat, making a hole through which the sperm head advances to reach the surface of the oocyte proper before fusing with it. In the sea urchin, an acrosomal protein called bindin adheres to the extended inner acrosomal membrane; this is what mediates sperm head attachment to the vitelline envelope as well as fusion with the egg’s plasma membrane [3, 4]. In some species of sea urchins (e.g., Pseudocentrotus depressus), the AR may occur on a very thin vitelline envelope covering the egg proper [5] (Fig. 1). However, in many other species, the AR begins while spermatozoa pass through a jelly coat overlying the vitelline envelope. In the starfish, the AR occurs at the outer surface of a thick jelly coat [6]. In some other invertebrate species (e.g., the annelid Hydroides hexagonus), the AR begins at the outer border of the vitelline envelope [7]. In mammals, fully mature oocytes that are ready for fertilization are each surrounded by a thick vitelline envelope called the zona pellucida that in turn is surrounded by numerous follicular cells embedded in an acellular matrix (hyaluronic acid polymers). Collectively, these are known as the cumulus-oocyte complex. Although we are certain that spermatozoa undergo the AR by the time they enter the zona pellucida with the aid of active flagellar propulsion, the site where fertilizing spermatozoa begin their AR has been the subject of controversy. Early investigators, who examined cumulus-oocyte complexes collected from the oviducts of naturally mated or inseminated females, found spermatozoa with intact, modified, or no acrosomes within the cumulus at about the time of fertilization [8–14]. Yanagimachi and Phillips [14] inferred that most fertilizing hamster spermatozoa in vivo initiate their AR while advancing though the cumulus. Other investigators, in particular those who studied mouse fertilization in vitro, opposed this idea and maintained that the site of the physiologically relevant AR is the zona pellucida [15–17]. This hypothesis was based on two observations: Acrosomeintact spermatozoa bind to the zona in vitro and then undergo the AR [18–20], and solubilized zona pellucida, in particular solubilized ZP3, binds specifically to the acrosomal region of sperm head and induces the AR as effectively as Ca2 ionophore in vitro [21–23]. It should be noted that no one has ever examined a single spermatozoon continuously from the beginning of the AR until the end of fertilization (syngamy). The spermatozoa that begin their AR on the zona pellucida might not be those that actually fertilize. Gahlay et al. [24] recently cast doubt on the ability of the zona pellucida to induce the AR. According to these investigators, zonae of transgenic mice (ZP2, ZP3) are unable to induce the AR, yet oocytes are still fertilized in these strains, suggesting that fertilizing spermatozoa undergo the AR either before their contact with the zona or during their passage through it. Jin et al. [25] approached the problem of sperm AR and fertility by video recording mouse spermatozoa after inseminating cumulus-enclosed oocytes in vitro. They placed a single cumulus-oocyte complex under a miniature coverslip, then slightly compressed and inseminated it with capacitated spermatozoa before undertaking continuous video recording. They used transgenic male mice whose spermatozoa express green fluorescent protein in their acrosomes. Sperm heads show green fluorescence when acrosomes are intact. This disappears upon initiation of the AR [26]. The strength of the study by Jin et al. [25] was that investigators could distinguish fertilizing spermatozoa from their nonfertilizing counterparts by examination of recorded images; this is something that no one has ever done before. The results of their exploration were startling. Most fertilizing mouse spermatozoa had already undergone the AR when first seen in the cumulus. Although a few fertilizing spermatozoa did undergo the AR on the zona, most acrosome-intact spermatozoa swam away from the zona without entering it. In other words, the initiation of sperm AR on the zona was the exception rather than the rule. This is consistent with what has been observed for guinea pig spermatozoa that exclusively bind to and penetrate the zona pellucida after the AR [27]. One wonders why previous researchers believed that acrosome-reacted mouse spermatozoa are infertile because of their inability to bind the zona [21]. The report by Jin et al. [25] reminds us that we must reinvestigate the process and mechanism of sperm-oocyte interactions by paying more attention to the spermatozoa that actually participate in fertilization. In many species, fertilization in vitro is certainly possible without an intact cumulus oophorus. Undoubtedly, the zona pellucida has the ability to induce or accelerate the AR, but the zona cannot be considered the sole innate substance that induces the physiological AR. Correspondence: FAX: 808 956 5474; e-mail: yana@hawaii.edu

Changes in the distribution of intramembranous particles and filipin-reactive membrane sterols during in vitro capacitation of golden hamster spermatozoa.

Abstract: Membrane alterations accompanying in vitro capacitation of hamster spermatozoa were examined using the freeze-fracture technique with or without use of filipin, a sterol-binding probe. In the spermatozoa prior to or at 10 min after start of incubation in capacitating medium, large (about 11 nm) and small (8-9 nm) intramembranous particles (IMPs) were present in the periacrosomal region of the sperm plasma membrane (PAPM). Filipin sterol complexes (FSCs) were densely (about 500/micron 2) distributed in the PAPM prior to incubation. The density of FSCs in the PAPM was reduced by 70-80% of the original density by 2 hr of incubation. At the same time, small patches of IMP-free areas appeared in the plasma membrane above the equatorial and middle segments of the acrosome. By the end of 3 hr of incubation, the majority of small IMPs had disappeared from the PAPM. Remaining large and small IMPs tended to aggregate in the PAPM. During incubation in capacitation medium, "cords," or linear arrangements of closely packed IMPs, appeared near the posterior ring of the sperm head. These observations strongly suggest that the acrosome reaction of the hamster spermatozoa is preceded by the removal (deletion) of filipin-reactive sterols (FRSs) and the disappearance of small IMPs from the lipid bilayer of PAPM.

Seminal characteristics, sperm fatty acids, and blood biochemical attributes in breeder roosters orally administered with sage (Salvia officinalis) extract

Abstract: Seminal characteristics and blood biochemical attributes were studied in breeder roosters orally administered with sage extract (SG), an herbal extract well known to have potent antioxidant activities. Sixty roosters (34 weeks old) were randomly allotted to five treatment groups to receive no SG, or orally administered with 110, 210, 320, or 420 mg SG/kg liveweight for 8 weeks. Semen samples were evaluated weekly. Blood samples were taken fortnightly and a total of 21 biochemical indices were measured to unmask the effects of SG (especially the adverse ones) on the clinical profile. Excluding the sperm concentration and seminal content of thiobarbituric acid reactive substances (sperm membrane lipid peroxidation index), other seminal traits exhibited one of the linear, quadratic, or cubic responses to the various levels of SG. The most improvements in total live sperm number and sperm membrane integrity (as determined by the hypoosmotic swelling test) were observed in birds receiving 210 and 320 mg SG/kg liveweight, respectively. Serum testosterone level was generally higher (cubically, P = 0.015), but serum copper was lower (linearly, P = 0.014) in SG-administered birds. Birds receiving 320 and 420 mg SG showed a decreased content of C18 : 2(n-6) in sperm plasma membrane. Other biochemical attributes or sperm fatty acids were not affected. It seems that most improvement in the seminal characteristics could be achieved 5–6 weeks following the administration of 210 and 320 mg SG/kg liveweight without any apparent adverse effect on the blood biochemical indices. The improvements, however, could not be attributed to the antioxidative effect of SG. Although it is hypothesised that an increased serum testosterone might have been involved, the underlying mechanism(s) remain(s) to be clarified.

Cytoplasmic Extrusion and the Switch From Creatine Kinase B to M Isoform are Completed by the Commencement of Epididymal Transport in Human and Stallion Spermatozoa

Abstract: Although in several species there is a relationship between epididymal sperm transport and fertility, in human in vitro fertilization (IVF), spermatozoa recovered from the caput epididymidis or even the rete testis are fertile. We studied two objective markers of sperm maturity in the sperm of men and stallions: creatine kinase (CK) concentrations, which are a measure of cytoplasmic retention in immature spermatozoa, and the ratio of CK-M and CK-B isoforms (% CK-M/[CK-M + CK-B]), which is proportional to the incidence of mature sperm. The CK markers and the fertilizing function are closely related: Immature sperm with cytoplasmic retention do not bind to the zona, because during cytoplasmic extrusion, the sperm plasma membrane is also remodeled. We examined whether changes in sperm CK values are still ongoing during epididymal transport, or if cellular maturation is completed prior to the arrival of sperm in the caput epididymidis. The incidences of mature sperm in human caput and corpus epididymidis (studied in six men with obstructive azoospermia of various pathogeneses) were (mean ± SEM) 55.7 ± 2.2 and 49.3 ± 7.6%, respectively; and the sperm CK-M ratios in the caput epididymidis of three men were 72, 75, and 70%, values that are similar to those of ejaculated sperm. In four segments of the proximal and distal epididymis of three stallions (the origin of sperm was also verified by the position of the cytoplasmic droplet) and in ejaculate of five stallions, the incidences of mature sperm were 88.2 ± 6.2, 89.0 ± 6.7, 90.3 ± 7.8, 87.6 ± 5.9, and 86.7 ± 0.8%, and the respective CK-M ratios were 75.0 ± 8.7, 84.2 ± 2.9,87.9 ± 1.2, 92.5 ± 1.5, and 69.3 ± 3.5%. There were no differences in the incidences of mature and immature spermatozoa or in CK-M ratios among sperm arising from the various epididymal regions or from the ejaculate in men or stallions. Thus, the cellular maturation events in sperm, as detected by the CK markers, are completed by the time the sperm commences epididymal transport. These findings are in agreement with the IVF fertility of sperm aspirated from the male reproductive tract. The data may also suggest that the primary role of sperm epididymal transport in men is to remodel the plasma membrane to enhance sperm functional integrity in the diverse environments of the male and female reproductive tracts prior to fertilization.