Fertilization of the starfish Astropecten aurantiacus

In the starfish Astropecten aurantiacus the acrosome reaction occurs when the spermatozoon contacts the outer surface of the jelly layer. A long thin acrosomal filament is extruded from the anterior region of the spermatozoon and establishes contact with the oocyte surface. This latter interaction initiates the movement of the spermatozoon to the oocyte surface, formation of the fertilization cone and the cortical reaction. The first detectable electrical change across the oocyte plasma membrane during interaction with the spermatozoon is the fertilization potential (FP) which occurs simultaneously with the cortical reaction. The FP is probably the electrical result of the modification of the oocyte plasma membrane during cortical exocytosis. There are no primary step-like depolarizations during fertilization of starfish oocytes, which contrasts with the situation in sea urchin eggs [see 13]. We suggest that the difference in electrical response to fertilization of starfish oocytes and sea urchin eggs may be attributed to the location of the acrosome reaction in these animals and not to their different meiotic states.     

东方扁虾精子的超微结构

利用电镜研究了东方扁虾（Ｔｈｅｎｕｓ ｏｒｉｅｎｔａｌｉｓ）精子的形态和结构。精子由核、膜复合物区和顶体区３部分组成。核内含非浓缩的染色质、微管及细纤维丝,外被核膜;５～６条辐射臂自核部位伸出,臂内充满微管。膜复合物区位于核与顶体之间,由许多膜片层结构及其衍生的囊泡共同组成。顶体区由顶体囊和围顶体物质组成,顶体结构复杂,由顶体帽、内顶体物质和外顶体物质等构成;围顶体物质呈细颗粒状,主要分布于顶体囊     

The Acrosome Reaction in Ciona intestinalis (Ascidia, Tunicata)

An acrosome reaction occurs by fusion between the acrosomal outer membrane and the plasmalemma enclosing the acrosome in Ciona intestinalis spermatozoa. The fusion seems to proceed along the peripheral margin of the acrosome, which causes vesiculation. The membrane bound vesicle formed by this process is probably shed by the sperm. The acrosomal inner membrane is exposed and becomes a part of the plasmalemma enclosing the anterior region of the sperm head. During this process, any acrosomal substance might be released through the opening formed by membrane fusion. The acrosome reaction most likely occurs in C. intestinalis spermatozoa, via vesiculation, in fundamentally the same way as observed in mammalian spermatozoa.     

Acrosome reaction in sperm of the toad,bufo bufo japonicus

The acrosome in the sperm of the toad, Bufo bufo japonicus, consists of a membrane-limited acrosomal cap and a fibrous perforatorium. When sperm are incubated with the oviducal pars recta extract (PRE) for 30–60 min, the outer acrosomal membrane fuses with the overlying plasma membrane at several points with concomitant loss of the contents of the acrosomal cap. The inner acrosomal membrane thus exposed fuses with the plasma membrane at the caudal end of the acrosomal region. This PRE-induced acrosome reaction is completely inhibited by soybean trypsin inhibitor. Sperm found in the innermost jelly layer of inseminated eggs possess an intact acrosome, but those either passing through the vitelline coat or localizing in the perivitelline space are acrosome-reacted in the same manner as when treated with PRE. These observations, combined with recent evidence showing involvement of the pars recta substance in fertilization, indicate that the acrosome reaction occurring in a fertilizing sperm at or near the surface of the vitelline coat is a response to a substance that is derived from the pars recta and deposited in the vitelline coat.     

Fine Structural Changes in the Acrosome Reaction of the Japanese Abalone, Haliotis disus

The spermatozoon of the Japanese abalone, Haliotis discus , and its structural changes during the acrosome reaction were observed by electron microscopy. The spermatozoon has a huge acrosome in the shape of a hanging bell or a forefinger with a deep fossa at the posterior end being filled with a bundle of microfilaments. The membranes of the acrosomal apex, the so-called trigger region, are structurally discernible from those of other acrosomal regions. Following the trigger region, a unique structure under the acrosomal membrane covers the surface of the acrosomal content in the form of a truncated cone.
The acrosome reaction occurs in the jelly layer very close to the egg envelope. First, the membranes at the apex of the acrosome are vesiculated, followed by the formation of a narrow gap between the outer acrosomal membrane and the acrosomal content. Next, the bundle of micro-filaments elongates, running through the center of the acrosome, reaching the trigger region and protruding out of the acrosomal top. Then release of the acrosomal content occurs in two steps, disclosing the "membrane undercoating structure" that comprises globular particles with a fuzzy material connecting them. This resembles the undercoat network found in erythrocytes.     

The acrosomal membrane of boar sperm: a Golgi-derived membrane poor in glycoconjugates

The acrosome is a large secretory vesicle of the sperm head that carries enzymes responsible for the digestion of the oocyte's investments. The event leads to sperm penetration and allows fertilization to occur. Release of the acrosomal enzymes is mediated by the interaction between sperm acrosomal and plasma membranes (acrosome reaction). Biochemical characterization of the acrosomal membrane has been restrained by a lack of methods to isolate uncontaminated fractions of the membrane. Here, we use new methods to expose the membrane to in situ cytochemical labeling by lectin-gold complexes. We study the topology and relative density of glycoconjugates both across and along the plane of the acrosomal membrane of boar sperm. Detachment of the plasma membrane from glutaraldehyde-fixed cells exposed the cytoplasmic surface of the acrosome to the lectin markers; freeze-fractured halves of the acrosomal membrane were marked by "fracture-label" (Aguas, A. P., and P. Pinto da Silva, 1983, J. Cell Biol. 97:1356-1364). We show that the cytoplasmic surface of the intact acrosome is devoid of binding sites for both concanavalin A (Con A) and wheat germ agglutinin (WGA). By contrast, it contains a high density of neuraminidase-resistant anionic sites detected by cationic ferritin. On freeze-fractured sperm, the receptors for Con A partitioned with the exoplasmic membrane half of the acrosomal membrane. The Con A-binding glycoconjugates were accumulated on the equatorial segment of the membrane. A low density of WGA receptors, as well as of intramembrane particles, was found on the freeze-fracture halves of the acrosomal membrane. The plasma membrane displayed, in the same preparations, a high density of receptors for both Con A and WGA. We conclude that the acrosome is limited by a membrane poor in glycoconjugates, which are exclusively exposed on the exoplasmic side of the bilayer. Regionalization of Con A receptors on the acrosome shows that sperm intracellular membranes, like the sperm surface, express domain distribution of glycocomponents.     

THE ACROSOME REACTION IN MYTILUS EDULIS : I. Fine Structure of the Intact Acrosome

The intact acrosome of the Mytilus edulis spermatozoon consists of a conical vesicle, the basal side of which is deeply invaginated so that the whole vesicle forms a sheath around a very slender axial rod, about 2.7 µ long, inserted in a tube passing through the nucleus. The annular base of the acrosomal vesical is filled with a homogeneous substance; the outer wall of the vesicle is lined with a somewhat irregular layer of a particulate substance interspersed with very fine tubular elements, and its lumen is nearly filled by a strand of material which extends from the inner tip of the invagination to the apex of the acrosome. The lumen of the invagination appears empty except for the rod and a delicate sleeve-like structure which surrounds it. The plasma membrane of the sperm cell lies in immediate contact with the acrosomal membrane over its whole outer surface. In its general organization, this molluscan acrosome shows a rather close homology with that of the annelid Hydroides.     

锯缘青蟹精子超微结构的研究

利用光镜和电镜观察了锯缘青蟹成熟精子的形态和超微结构。精子呈陀螺形，无鞭毛，在较宽的一端环生着１０余辐射臂。精子由球状的顶体、核杯以及核衍生的辐射臂三部分组成。顶体包括顶体管和顶体囊，后者包绕在顶体管的中央管周围，并可分为头帽带，内层和外层区。顶体被杯状的核包裹，仅头帽露于精子表面。成熟的精子中，位于核杯和顶体管之间的核膜出现局部断续或消失，中心粒和一些胞器出现的核杯腔中。     

FINE STRUCTURE OF THE SPERMATOZOON OF HYDROIDES HEXAGONUS (ANNELIDA), WITH SPECIAL REFERENCE TO THE ACROSOMAL REGION

This paper describes in some detail the structure of the acrosomal region of the spermatozoon of Hydroides as a basis for subsequent papers which will deal with the structural changes which this region undergoes during fertilization. The material was osmium-fixed and mild centrifugation was used to aggregate the spermatozoa from collection to final embedding. The studies concern also the acrosomal regions of frozen-thawed sperm prepared by a method which previously had yielded extracts with egg membrane lytic activity. The plasma membrane closely envelops four readily recognizable regions of the spermatozoon: acrosomal, nuclear, mitochondrial, and flagellar. The acrosome consists of an acrosomal vesicle which is bounded by a single continuous membrane, and its periphery is distinguishable into inner, intermediate, and outer zones. The inner and intermediate zones form a pocket into which the narrowed apex of the nucleus intrudes. Granular material adjoins the inner surface of the acrosomal membrane, and this material is characteristically different for each zone. Centrally, the acrosomal vesicle is spanned by an acrosomal granule: its base is at the inner zone and its apex at the outer zone. The apex of the acrosomal granule flares out and touches the acrosomal membrane over a limited area. In this limited area the adjoining granular material of the outer zone is lacking. The acrosomal membrane of the inner zone is invaginated into about fifteen short tubules. The acrosomal membrane of the outer zone is closely surrounded by the plasma membrane. At the apex of the acrosomal region a small apical vesicle is sandwiched between the plasma membrane and the acrosomal membrane. Numerous frozen-thawed specimens and occasional specimens not so treated show acrosomal regions at the apex of which there is a well defined opening or orifice. Around the rim or lip of this orifice plasma and acrosomal membranes may even be fused into a continuum. The evidence indicates that the apical vesicle and the parts of the plasma and acrosomal membranes which surround it constitute a lid, and the rim of this lid constitutes a natural "fracture line" or rim of dehiscence. Should fracture occur, the lid would be removed and the acrosomal vesicle would be open to the exterior.     

Morphological identification of sperm receptors above egg microvilli in the polychaete, Neanthes japonica

A fine-structural study of sperm-egg interactions in the polychaete Neanthes japonica was carried out. Unfertilized eggs are surrounded by a chorion 0.6-0.7 micrometers thick. Oocyte microvilli are inserted into the inner layer of the chorion. The outer layers of the chorion are opened just above the tips of the microvilli, where a membrane vesicle (microvillus tip vesicle, about 0.2 micrometers in diameter) plugs the chorion's opening. During fertilization, the acrosomal process of the sperm fuses with an egg microvillus within 1 min of insemination. All the microvillus tip vesicles disappear from the chorion surface within 5 min of insemination. When eggs, which are prefixed with glutaraldehyde, are inseminated, numerous sperm undergoing the acrosome reactions attach to the eggs. In the majority of these sperm, the tip of acrosomal process which is coated with the acrosomal content, adhere to a microvillus tip vesicle. These findings suggest that the microvillus tip vesicle serves as a sperm receptor, which induces the acrosome reactions and adhere to the sperm acrosomal process. The adhesion of the acrosomal process to the microvillus tip vesicle seems to be a prerequisite event for its fusion with the microvillus.     

Ultrastructure of the Tubificid Acrosome (Annelida, Oligochaeta)

The later morphogenesis of the acrosome of Limnodriloides winckelmanni and Rhyacodrilus arthingtonae is compared with that in Enchytraeus and in earthworms. After superposition of the acrosome on the tip of the nucleus the manchette continues apically beyond the nucleus to ensheath the acrosomal tube. At the posterior limit of, and probably contained in, the spacious/ terminal primary acrosomal vesicle is an electron-dense ring. A domed protrusion into the floor of the primary vesicle is tentatively regarded as the secondary acrosome vesicle. The axial rod when first observed is attached to the vesicle complex. Later, the rod detaches and extends deeply into the acrosome tube. A membrane ensheathes the tubificid axial rod but its exact homology with the complex layers surrounding the lumbricid or megascolecid axial rod is not clear. The domed apical region of the tubificid acrosome is probably a persistence of the primary acrosome vesicle and it is deduced that the acrosome vesicle surrounding the axial rod in lumbricids and megascolecids is a product, by invagination, of the secondary acrosome vesicle only.     

Ultrastructure of spermatogenesis in the sea star,Asterina minor

The ultrastructural features of spermatogenesis were investigated in the hermaphroditic sea star Asterina minor. The primordial germ cells in the genital rachis contain small clusters of electron-dense material (nuage material) and a stack of annulate lamellae. They also have a flagellum and basal body complex situated close to the Golgi complex. After the development of the genital rachis into the ovotestis, spermatogenic cells increase in number and differentiation begins. Nuage material is observed in spermatogonia, but it gradually disappears in spermatocytes. The annulate lamellae do not exist beyond the early spermatogonial stage. By contrast, a flagellum and basal body complex are found throughout spermatogenesis. The Golgi-derived proacrosomal vesicles appear in the spermatocyte and coalesce to form an acrosomal vesicle in the early spermatid. The process of acrosome formation is as follows: (1) a lamella of endoplasmic reticulum (ER) continuous with the outer nuclear membrane encloses the posterior portion of the acrosomal vesicle; (2) the vesicle attaches to the cell membrane with its anterior portion; (3) periacrosomal material accumulates in the space between the acrosomal vesicle and the ER; (4) the nucleus proper changes its features to surround the acrosome; (5) amorphous, electron-dense material is deposited under the electron-dense disk; and (6) the nucleus forms a hollow opposite the electron-dense material.     

锯缘青蟹精子发生的超微结构

采用透射电镜观察锯缘青蟹精子发生过程中超微结构的变化,结果表明：精原细胞椭圆形,染色质分布于核膜周围,胞质中具嵴少的线粒体,内质网小泡等。初级精母细胞染色质呈非浓缩状,胞质中具众 内质网小泡,特殊的膜系及晶格状结构。次级精母细胞核质间出现由内质小泡聚集成的腔。     

Substructure of a cytoskeletal complex associated with the hamster sperm acrosome

Whole mount and thin section preparations of intact and selectively disrupted hamster spermatozoa revealed an organized array of cytoplasmic filaments associated with specific regions of the acrosome. The filaments were localized along the ventral surface of the spermatozoon and extended from its tip, distally to the anterior margin of the equatorial segment. Individual filaments were 11-13 nm in diameter and they were aligned parallel to one another to form a two-dimensional sheet oriented in the long axis of the spermatozoon. The filament complex adhered preferentially to the cytoplasmic surface of the outer acrosomal membrane rather than the plasma membrane. Examination of disrupted spermatozoa revealed that the distribution of this cytoskeletal assembly correlated with the distribution of a specific acrosomal matrix component. The possible role of this complex in the acrosome reaction or in the organization of acrosomal matrix domains is discussed.     

Presence of ATPase and alkaline phosphatase activities in the starfish sperm acrosome

ATPase activity was cytochemically detected in the peripheral acrosomal component of ionophore-reacted sperm, while alkaline phosphatase activity was demonstrated in the upper and central components of the acrosome and, at fertilization, at the site of sperm-oocyte binding. Supernatants of ionophore treated sperm suspensions were assayed for ATPase, alkaline and acid phosphatase activities. Results suggest that alkaline phosphatase may be involved both in the acrosomal reaction and oocyte jelly lysis but the function of the acrosomal ATPase remains unknown.     

Fertilization in a crab: I. Early events in the ovary,and cytological aspects of the acrosome reaction and gamete contacts

Early events in fertilization were studied in Carcinus maenas by in vitro experiments and ultrastructural analysis; some were found to occur in the lumen of ripe ovaries. The acrosome reaction generally conformed to the usual Reptantia Decapoda pattern. However, a prominent membrane system continuous with the nuclear envelope and located close to the base of the acrosome tubule characterized the type of spermatozoon observed in Carcinus maenas. Such complex anatomical connections linking the three parts of the reacted spermatozoon (acrosome tubule, membrane system and nucleus envelope) may be significant in relation to the membrane system's contribution to the acrosome reaction. The outer layer of the everted acrosomal vesicle was found to comprise tubular elements ending in bell-shaped corpuscles, deeply interdigitated with the oolemma microvilli during the establishment of the initial contacts between the reacted spermatozoon and the egg plasma membrane. At the site of contact, the oolemma formed a minute fertilization cone, locally depressed by the acrosome tubule. During these early fertilization events, the nucleus, like the other spermatozoon components, was seen to penetrate the egg coatings first, and later to be located near the oolemma.     

The fine structure of the sperm of a holothurian and an ophiuroid

The fine structure of the mature sperm of the holothurian, Cucumaria miniata, and the ophiuroid, Ophiopholis aculeata, is described with particular reference to their acrosomal and centriolar satellite complexes, and compared to the sperm of other echinoderms. In Cucumaria, the acrosome is in the form of a diffuse acrosomal vesicle. It is unusual in that it apparently lacks an acrosomal membrane. A membrane separating the acrosomal vesicle from the periacrosomal material may not be equivalent to a typical inner acrosomal membrane. In Ophiopholis, the acrosome is dense, with some internal substructure, and is enclosed by a complete acrosomal membrane. In both species, the acrosome is partially surrounded by an amorphous periacrosomal mass. There is a notable absence of a subacrosomal depression and associated structures as found in other echinoderm sperm. The centriolar satellite complex (CSC) is essentially identical in both species. A reconstruction of the CSC is presented. The CSC consists of nine satellites radiating angularly from the distal centriole, each bifurcating at a dense node before inserting on a marginal ring containing circumferential microtubules. The ring is probably a cytoskeletal element. Immediately below the satellites are nine Y-shaped connectives. connecting each of the axonemal alpha doublets to the flagellar membrane.     

东方扁虾精子发生的超微结构

应用电镜技术研究了东方扁虾（Thenus orientalis)精子发生的全过程,精原细胞呈椭圆形,其染色质分布较均匀,线粒体集中于细胞一端形成“线粒体区”。初级精母细胞较大,染色质凝聚成块,次级精母细胞核质间常出现大的囊泡,胞质内囊泡丰富而线粒体数量却明显减少,早期精细胞核发生极化、解聚,部分胞质被抛弃。中期精细胞外观呈金字塔形,分为三区;正在形成的顶体位于塔顶,核位于塔基部,居间的细胞质基质内富含膜复合物,后期精细胞顶体进一步分化。形成顶体帽和内、外顶体物质等三个结构组份。成熟精子核呈盘状或碗状,具有5-6条内部充满微管的辐射臂。     

Capacité des spermatozoïdes à se fixer sur la zone pellucide

After liberation from the seminiferous epithelium, the spermatozoa (SPZ), undergo in the epididymis a serie of functional and metabolic modifications resulting the capacity to ensure fertilization. Fertilization is the fundamental process in sexual reproduction as it permits the initiation and the formation of a new being by the fusion of two germinal cells: the male gamete (spermatozoa) and the female gamete (oocyte). For fertilization to occur the SPZ must recognize the zona pellucida (ZP), bind to it, penetrate it and fuse with the oocyte plasma membrane. Sperm binding to the ZP is an early, crucial event leading to fertilization and pre-embryo development. In mammals, sperm-ZP binding follows a serie of steps that occur in a well-defined chronological order: a) A loose association between SPZ and ZP referred to as «attachment». This shortlived interaction is heterospecific. b) Attachment is followed by a more distinct and persistent association of SPZ with ZP, thus called «binding». This sperm-zona interaction is species-specific, irreversible and mediated by complementary receptors present on the SPZ head and the ZP. c) The bound SPZ then undergoes the acrosome reaction (AR). Which involves fusion and vesiculation of the SPZ outer acrosomal membrane and plasma membrane leading to the release of acrosomal contents and the exposure of the inner acrosomal membrane. This AR is essential for SPZ passage through the ZP and to access to the oocyte plasma membrane where gamete fusion occurs.     

Isolation and characterization of a macromolecular complex associated with the outer acrosomal membrane of bovine spermatozoa

The acrosomal membrane of mammalian spermatozoa is segregated into domains of different structure and function. The outer acrosomal membrane of the apical and principal segments is the only domain to participate in the membrane fusion events of the acrosome reaction, but the molecular basis for this function is not resolved. In previous studies of bovine spermatozoa, we noted that a unique structural feature of the outer acrosomal membrane was an adherent layer of electron-dense material on its luminal surface (ES Surface, Branton et al., 1975). In this study, we report the isolation of this material and we describe both its structural and biochemical characteristics. Cauda epididymal spermatozoa were extracted with 1% Triton X-100 to solubilize cytoplasmic and membrane components; detergent treatment solubilized the outer acrosomal membrane but not its adherent electron-dense complex. Homogenization released this complex from the spermatozoa and it was then resolved into a homogeneous fraction by centrifugation on Percoll density gradients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of this fraction revealed a spectrum of polypeptides including components of 290 kDa, 280 kDa, 260 kDa, 115 kDa, 81 kDa, 58 kDa, and 46 kDa and a family of interrelated components in the 34-12 kDa range. This complex possesses protein kinase activity that phosphorylates specific endogeneous polypeptides in a cAMP-independent manner. In addition, several polypeptides of the 34-12 kDa family specifically bind 125I-calmodulin. One consistent structural response of the isolated complex was that its edges wound into a spiral configuration. We speculate that this membrane-associated assembly plays a functional role in the membrane fusion events of the acrosome reaction.