金鱼精子质膜和核膜的区域特异性

本文结合采用扫描和透射电子显微镜(包括冷冻断裂-蚀刻、超薄切片以及细胞化学染色法),研究了金鱼精子的超微结构特征,结果表明金鱼精子的质膜和核膜都具有区域特异性:1)精子质膜内大部分区域含有许多蛋白颗粒,但在特定区域内,蛋白颗粒呈有序排列,构成晶格状结构。2)精子头颈部和尾部均有液泡密集之处,凡是覆盖着液泡区的质膜内,几乎都不含有蛋白颗粒。3)液泡区能被细胞化学方法染成致密色,表明内含糖蛋白。4)核膜孔只集中存在于靠近颈部的核膜上,而其他部分则没有。本文对上述诸点进行了讨论。     

The plasama membrane of Xenopus laevis spermatozoon

Xenopus laevis sperm plasma membrane ultrastructure has been studied by means of freeze-fracture, deep-etching, and lectin-gold binding. Xenopus spermatozoa differ from those of other species in that their plasma membrane does not exhibit topographical domains. In fact, no geometric arrangement or characteristic array of particles is present on fractured plasma membrane. Fractures rarely occur in acrosomal or nuclear membranes. Wheat germ agglutinin receptors are distributed homogeneously, on the plasma membrane of the sperm head and tail.     

Distribution of intramembranous particles and filipin-sterol complexes in mouse sperm membranes: polyene antibiotic filipin treatment

The distribution of intramembranous particles (IMPs) and membrane filipin-sterol complexes (FSC) was examined ultrastructurally in mouse spermatozoa from the male reproductive tract and ejaculates. IMPs were qualitatively analyzed on freeze-fracture replicas of glutaraldehyde-fixed tissue, while membrane FSC were quantitatively analyzed on replicas of filipin-treated cells. The distribution pattern of IMPs of mouse spermatozoa was fundamentally similar to that of other mammalian spermatozoa. 1) In the head, the plasma membrane had a heterogeneous population density, e.g., few IMPs on the acrosomal region, particularly few on the marginal segment, and somewhat regularly arranged IMPs on the postacrosomal region. The acrosomal membrane had many IMPs in hexagonal arrays. The nuclear membrane had many IMPs on the P-face, few IMPs on the variegated E-face, and an intense population density on the P-face of the basal plate. 2) In the neck, the plasma membrane had many IMPs with square arrangements of small IMPs in some areas on the P-face; the redundant nuclear membrane had a few IMPs on both P- and E-faces. 3) In the tail, the plasma membrane had diagonal rows of IMPs in some areas amongst larger IMPs on the middle piece, while it had "zippers" composed of IMPs running parallel to the axis on the principal piece. The distribution of sperm membrane FSC may be summarized as follows: 1) In the head, the acrosomal plasma membrane, which was heavily labeled with filipin, had much more FSC in the equatorial segment than in the marginal segment throughout the study. The postacrosomal plasma membrane generally had no FSC, but some sperm in ejaculates were slightly positive to filipin. The acrosomal membranes (both outer and inner) had no FSC. The nuclear membrane in the main part of the head had less FSC in vas deferens and ejaculated sperm than in the epididymal sperm. The nuclear membrane on the basal plate had no FSC. 2) In the neck, the plasma membrane had little FSC. The redundant nuclear envelope had scattered FSC with a higher incidence in the epididymal sperm than in those from the vas deferens and ejaculates. The membrane scroll, which was elongated from the extreme caudal end of the redundant nuclear envelope, had abundant FSC in the vas deferens and ejaculated sperm. 3) The tail plasma membrane (both middle and principal piece), which was weakly labeled with filipin, had less FSC in sperm from the vas deferens and ejaculates than in those from the epididymis. The limiting membrane covering the mitochondria had no FSC.     

Sperm head membrane reorganisation during capacitation

The sperm cell has a characteristic polarized morphology and its surface is also highly differentiated into different membrane domains. Junctional protein ring structures seal the surface of the mid-piece from the head and the tail respectively and probably prevent random diffusion of membrane molecules over the protein rings. Despite the absence of such lateral diffusion-preventing structures, the sperm head surface is also highly heterogeneous. Furthermore, lipid and membrane protein ordering is subjected to changes when sperm become capacitated. The forces that maintain the lateral polarity of membrane molecules over the sperm surface, as well as those that cause their dynamic redistribution, are only poorly understood. Nevertheless, it is known that each of the sperm head surface regions has specific roles to allow sperm to fertilize the oocyte: a specific region is devoted to zona pellucida binding, a larger area of the sperm head surface is involved in the acrosome reaction (intracellular fusion), while yet another region is involved in egg plasma membrane binding and fertilization fusion (intercellular membrane fusion). All three events occur in the area of the sperm head where the plasma membrane covers the acrosome. Recently, lipid ordered microdomains (lipid rafts) were discovered in membranes of many biological specimens including sperm. In this review, we cover the latest insights about sperm lipid raft research and discuss how sperm lipid raft dynamics may relate to sperm-zona binding and the zona-induced acrosome reaction.     

Capacitation-dependent reorganization of microdomains in the apical sperm head plasma membrane: functional relationship with zona binding and the zona-induced acrosome reaction

For sperm to successfully fertilize an oocyte, it needs to pass through certain steps prior to, during and after initial recognition of the zona pellucida (ZP). During capacitation, the surface of the sperm head becomes remodelled, priming it to bind to the ZP and subsequently to undergo the ZP-induced acrosome reaction. During capacitation, sperm ZP-binding proteins are ordered in functional protein complexes that only emerge at the apical tip of the sperm head plasma membrane; this is also functionally the exclusive sperm surface area involved in primary ZP binding. After primary ZP binding, the same area is probably involved in the induction of the acrosome reaction. A combination of biochemical and proteomic membrane protein techniques have enabled us to dissect and highly purify the apical sperm plasma membrane area from control and capacitated sperm cells. The actual ZP-binding proteins identified predominantly belonged to the sperm membrane-associated family members of spermadhesins (AQN-3) and were present in the aggregating lipid ordered membrane microdomains (lipid rafts) that emerged during in vitro capacitation in the apical ridge area of the sperm head plasma membrane. This clustering of these rafts was dependent on the presence of bicarbonate (involved in protein kinase A activation) and on the presence of albumin (involved in cholesterol removal). Remarkably, cholesterol removal was restricted to the non-raft membrane fraction of the sperm plasma membrane, but did not cause any depletion of cholesterol in the raft membrane fraction. Interestingly, sperm SNARE proteins (both VAMP from the outer acrosomal membrane, as well syntaxin from the apical sperm head plasma membrane) shared lateral redistribution properties, along with the ZP-binding protein complex and raft marker proteins. All of these were recovered after capacitation in detergent-resistant membrane preparations from sperm thought to represent membrane lipid rafts. We inferred that the capacitation-dependent formation of an aggregated lipid ordered apical ridge surface area in the sperm head plasma membrane was not only relevant for ZP-binding, but also for the ZP-induced acrosome reaction.     

The spermatozoa of ascidians: Acrosome and nuclear envelope

Summary The spermatozoon of Ascidia callosa has a head with a wedge-shaped tip. Between the nuclear envelope and the plasmalemma, at the tip of the head, there are one or two previously undescribed vesicles, 45 to 55 nm in diameter. These vesicles have the characteristics of an acrosome. Their role in the process of fertilization has not been determined. Ultrastructural studies of sperm activation are needed, but claims that the spermatozoa of ascidians do not have an acrosome should be reconsidered.Behind the tip of the sperm there are pores in the nuclear envelope. This part of the envelope also contains a dense band of amorphous material that may have a supportive function. A nearly identical structure, associated with pores has been found in the spermatozoon of Boltenia villosa. An analysis of the nuclear envelope of Ascidia callosa indicates that the same structure has previously been misinterpreted as an acrosome in the spermatozoon of Ascidia nigra.     

Probing the dynamics of intact cells and nuclear envelope precursor membrane vesicles by deuterium solid state NMR spectroscopy

Membrane dynamics is an essential part of many cellular mechanisms such as intracellular trafficking, membrane fusion/fission and mitotic organelle reconstitution. The dynamics of membranes is dependent primarily on their phospholipid and cholesterol composition and how these molecules are ordered in relation to one another. To determine the physical status of membranes in whole cells or purified membranes of subcellular compartments we have developed a novel application exploiting solid-state (2)H-NMR spectroscopy. We utilise this method to probe the dynamics of intact sperm and nuclear envelope precursor membranes. We show, using mass spectrometry, that either multilamellar or small unilamellar vesicles of deuterium-labelled palmitoyl-oleoylphosphatidylcholine can be used to probe the dynamics of sperm cells or nuclear envelope precursor membrane vesicles, respectively. Using (2)H-NMR we determine the order parameters of sperm cells and nuclear envelope precursor membrane vesicles. We demonstrate that whole sperm membranes are more dynamic than nuclear envelope precursor membranes due to the higher cholesterol levels of the latter. Our new application can be exploited as a generic method for monitoring membrane dynamics in whole cells, various subcellular membrane compartments and membrane domains in subcellular compartments.     

Probing the dynamics of intact cells and nuclear envelope precursor membrane vesicles by deuterium solid state NMR spectroscopy

Membrane dynamics is an essential part of many cellular mechanisms such as intracellular trafficking, membrane fusion/fission and mitotic organelle reconstitution. The dynamics of membranes is dependent primarily on their phospholipid and cholesterol composition and how these molecules are ordered in relation to one another. To determine the physical status of membranes in whole cells or purified membranes of subcellular compartments we have developed a novel application exploiting solid-state ²H-NMR spectroscopy. We utilise this method to probe the dynamics of intact sperm and nuclear envelope precursor membranes. We show, using mass spectrometry, that either multilamellar or small unilamellar vesicles of deuterium-labelled palmitoyl-oleoylphosphatidylcholine can be used to probe the dynamics of sperm cells or nuclear envelope precursor membrane vesicles, respectively. Using ²H-NMR we determine the order parameters of sperm cells and nuclear envelope precursor membrane vesicles. We demonstrate that whole sperm membranes are more dynamic than nuclear envelope precursor membranes due to the higher cholesterol levels of the latter. Our new application can be exploited as a generic method for monitoring membrane dynamics in whole cells, various subcellular membrane compartments and membrane domains in subcellular compartments.     

A transmission electron microscopy investigation: the membrane complex in spermatogenesis of <Emphasis Type="Italic">Fenneropenaeus chinensis</Emphasis>

The transforming characteristics of the membrane complex in spermatogenesis of Fenneropenaeus chinensis have been studied by using transmission electron microscopy. Two types of membrane complex have been investigated based on their sources: one originating from nucleus and the other from cytoplasm. The first one, consisted of annular structures, monolayer membrane blebs, and double or multi-lamellar membrane vesicles, emerges in the primary spermatocyte, then diffuses with the nuclear membrane and finally enters the cytoplasm. This type of membrane complex seems to play an important role in the materials transfusion from nucleus to cytoplasm, and it mainly exists inside the primary spermatocyte with some inside the secondary spermatocyte. The latter, originated from cytoplasm, is formed during the anaphase of spermiogenesis. It also exists in mature sperm, locating at both sides of the nucleus under the acrosomal cap. This type of membrane complex mainly comprises rings of convoluted membrane pouches, together with mitochondria, annular lamina bodies, fragments of endoplasmic reticulum, nuclear membrane and some nuclear particles. It releases vesicles and particles into the acrosomal area during the formation of the perforatorium, suggesting a combined function of the endoplasmic reticulum, mitochondria and Golgi’s mechanism.     

ADAM7 is associated with epididymosomes and integrated into sperm plasma membrane

During epididymal transit, mammalian sperm acquire selected proteins secreted by the epididymis. We previously showed that a disintegrin and metalloprotease (ADAM) 7 is expressed specifically in the epididymis and transferred to the sperm surface during epididymal transit. Here, we show that mouse ADAM7 secreted to the epididymal lumen is associated with membranous vesicles known as epididymosomes. Furthermore, we found that ADAM7 can be transferred directly from epididymal vesicles to sperm and that it is an integral plasma membrane protein in sperm. Thus, our study provides new information regarding the unique mode of secretion and interaction of ADAM7 during the epididymis-to-sperm transfer process.