透明带的精子受体在ZP3的O—糖链上

哺乳动物的受精过程主要包括几个步骤 ,精子与卵子相遇后 ,精子结合到卵透明带上 ,引起精子的顶体反应 ,随后精子穿透透明带与卵细胞融合受精。精卵结合具有种属特异性 ,这种特异性结合是由精子表面的特异蛋白和卵透明带糖蛋白通过受体配体模式进行的。但是 ,卵透明带上的什么物质与精子识别和结合呢 ?近 30年来 ,这一领域的研究很活跃 ,也取得了很大的进展。1 .小鼠透明带糖蛋白ＺＰ3作为精子受体透明带是卵细胞膜外的一层特殊的非细胞结构 ,是精子与卵细胞识别和结合的部位。小鼠和其它研究过的哺乳类的透明带都是由少数几种糖蛋白组成 ,…     

人及哺乳动物受精与糖蛋白的关系

越来越多的研究表明精卵识别与精子质膜及卵透明带中所含糖蛋白有直接关系。在精卵识别中存在着精子受体和卵透明带（zona pellucida,ZP）配体相互作用的糖类识别机制及精子质膜与卵子质膜的糖蛋白识别。本文主要从结构功能上对与受精相关的精卵表面糖蛋白作一介绍。卵子表面受精相关的糖蛋白主要是ZP1、ZP2、ZP3。与卵子表面糖蛋白相比,精子表面参与精卵识别的糖蛋白种类较多,在SP56、SP95、PH－20、FA－1、甘露糖结合蛋白、顶体素、fertilin蛋白等。     

哺乳动物精卵相互作用的分子机制的研究进展

哺乳动物受精是由一系列有序步骤组成的复杂细胞相互作用过程组成,最终导致精卵质膜融合形成受精卵。近来运用基因组学和蛋白质组学技术在哺乳动物精子和卵子表面鉴定出若干可能参与精卵质膜粘附与融合过程的蛋白分子,并对其结构和生物学功能进行了研究,但精卵识别与融合的分子机理仍然不清楚。综述了与精卵识别和融合有关的蛋白的最新研究进展,为进一步研究精卵相互作用的分子机制提供参考。     

被子植物受精作用的分子和细胞生物学机制

被子植物双受精包括精-卵、精子-中央细胞两个融合过程。由于双受精深藏于母体组织中进行, 长期以来一直是植物有性生殖研究中的难点。近年来, 随着各种植物配子体cDNA文库的构建, 各种离体研究系统的建立和突变体分析的兴起, 极大地推动了被子植物受精作用研究的快速发展, 增进了人们对被子植物受精过程的分子和细胞生物学机制的深入了解。本文着重讨论受精作用的若干重要发育事件, 包括受精前卵器细胞对花粉管向胚珠定向生长的近距离引导信号, 精子的靶向运动,精、卵细胞相互作用和配子融合后卵细胞的激活与中央细胞发育的启动等。     

疱疹病毒膜融合的分子机制

囊膜病毒与宿主细胞的膜融合是病毒入侵宿主细胞的重要过程,这一过程涉及到病毒囊膜表面糖蛋白与宿主细胞表面受体之间的相互作用和构象变化．疱疹病毒有多个糖蛋白及不同类型的细胞作用受体,相应的受体-糖蛋白复合体构成方式也有多种,其引致的膜融合机制被认为是目前病毒融合机制研究中最复杂的,近年来被广泛研究并取得突破性进展．从病毒糖蛋白与相应受体的结构与功能、受体-糖蛋白复合体的形成与入侵途径,以及膜融合模式几个方面,全面综述疱疹病毒膜融合的分子机制,并展望了未来研究趋势．     

被子植物受精作用的分子和细胞生物学机制

被子植物双受精包括精-卵、精子-中央细胞两个融合过程。由于双受精深藏于母体组织中进行,长期以来一直是植物有性生殖研究中的难点。近年来,随着各种植物配子体cDNA文库的构建,各种离体研究系统的建立和突变体分析的兴起,极大地推动了被子植物受精作用研究的快速发展,增进了人们对被子植物受精过程的分子和细胞生物学机制的深入了解。本文着重讨论受精作用的若干重要发育事件,包括受精前卵器细胞对花粉管向胚珠定向生长的近距离引导信号,精子的靶向运动,精、卵细胞相互作用和配子融合后卵细胞的激活与中央细胞发育的启动等。     

糖蛋白物与发育

糖与蛋白质或脂类共价结合而成的糖蛋白、蛋白聚糖、糖脂以及脂多糖统称糖复合物 ,最近几年人们对糖复合物在生物发育过程中的作用进行了大量的研究 ,已经在许多方面取得了重大进展。1 .糖复合物与配子发生和受精配子发生和受精过程中有大量糖复合物的参与 ,他们在配子发生、精卵识别与受精以及受精完成后防止多精穿入的皮层反应等过程中发挥作用。哺乳动物精子表面有一层几百种糖蛋白组成的糖萼 ,其成熟是精子成熟的标志。射出的精子头部外表面的糖蛋白能阻止顶体酶的释放 ,在获能过程中该糖蛋白被雌性生殖管道分泌物中的酶降解后精子才获…     

绵羊精子膜上糖结合蛋白的探索

精卵细胞的识别是具有高度种属专一性的细胞识别现象。在海胆精子的顶体部位,存在着一类糖结合蛋白,称作bindin。它专一地与卵细胞上的透明带结合,半乳糖抑制这种结合。bindin可能涉及海胆精卵细胞之间的相互识别。为了探索在哺乳类动物中精卵细胞的识别是否可能基于同样的分子基础,我们利用绵羊精子进行了这方面的探索。     

短额负蝗配子发生过程中蓖麻凝集素受体的分布

利用凝集素细胞化学方法对短额负蝗Atractomorpha sinensis Bolivar配子发生过程中蓖麻凝集素（Ricinus communis agglutinin-Ⅰ,RCA-Ⅰ）受体分布进行了定位研究,旨在认识昆虫配子发生过程中β-半乳糖复合物的分布规律及意义。结果表明： 在短额负蝗精子发生过程中,RCA-Ⅰ在各期生精细胞膜上均有明显的阳性反应,变形期及成熟期精子头部为中强度阳性反应。卵子发生中,各阶段卵母细胞均为阳性反应,在卵母细胞生长期阳性反应达峰值,随着卵黄颗粒的逐渐形成,阳性反应逐渐减弱,成熟卵子中卵黄膜上重新出现中强度阳性反应。结果提示短额负蝗配子发生过程中β-半乳糖复合物的高度表达和修饰变化与其配子发生密切相关。     

被子植物受精机制的研究进展

被子植物的受精是一个复杂而精巧的过程。花粉管到达子房,通过退化助细胞进入胚囊,释放出两个精细胞。原来在花粉管中相互联结的两个精细胞在退化助细胞中分开,一个与卵细胞融合,另一个与中央细胞融合,完成双受精。目前对双受精过程中有关雌、雄配子识别的机制还知之甚少。本文介绍了目前被子植物精、卵细胞融合前后的细胞周期变化、退化助细胞的功能、精细胞在退化助细胞中迁移的研究动态、精细胞的倾向受精和卵细胞的激活等被子植物受精生物学领域中的一些新的研究成果和发展趋势。     

Full-length sequence of VERL,the egg vitelline envelope receptor for abalone sperm lysin

Abalone sperm use 16 kDa lysin to create a hole in the egg vitelline envelope (VE) by a species-specific, nonenzymatic mechanism. To create the hole, lysin binds tightly to VERL (the VE receptor for lysin), a giant, unbranched glycoprotein comprising 30% of the VE. Binding of lysin to VERL causes the VERL molecules to lose cohesion and splay apart creating the hole. Lysin and VERL represent a cognate pair of gamete recognition proteins, one male the other female, which mediate fertilization. The coevolution of such cognate pairs may underlie the establishment of species-specific fertilization which could be a component of the mechanism to achieve reproductive isolation and hence new species. Here we present the full-length cDNA sequence (11,166 bp) of VERL from the red abalone (Haliotis rufescens). There are 42 amino acids from the start Met residue to the beginning of the first 'VERL repeat'. Most of VERL (9981 bp; 89.4%) consists of 22 tandem repeats of a approximately 153 amino acid sequence that is predicted to be beta-sheet. The last VERL repeat is followed by 353 non-repeat amino acid residues containing a furin cleavage site (RTRR), a ZP domain and a hydrophobic COOH-terminus with a 3' UTR of only 10 nucleotides. VERL repeats 3-22 have been subjected to concerted evolution and consequently have almost identical sequences. Curiously, comparisons of repeats from other species shows that repeats 1 and 2 of red abalone VERL have not been subjected to concerted evolution since the divergence of the red species from the other six California species.     

Polymorphism in abalone fertilization proteins is consistent with the neutral evolution of the egg's receptor for lysin (VERL) and positive darwinian selection of sperm lysin

The evolution of species-specific fertilization in free-spawning marine invertebrates is important for reproductive isolation and may contribute to speciation. The biochemistry and evolution of proteins mediating species-specific fertilization have been extensively studied in the abalone (genus Haliotis). The nonenzymatic sperm protein lysin creates a hole in the egg vitelline envelope by species-specifically binding to its egg receptor, VERL. The divergence of lysin is promoted by positive Darwinian selection. In contrast, the evolution of VERL does not depart from neutrality. Here, we cloned a novel nonrepetitive region of VERL and performed an intraspecific polymorphism survey for red (Haliotis rufescens) and pink (Haliotis corrugata) abalones to explore the evolutionary forces affecting VERL. Six statistical tests showed that the evolution of VERL did not depart from neutrality. Interestingly, there was a subdivision in the VERL sequences in the pink abalone and a lack of heterozygous individuals between groups, suggesting that the evolution of assortative mating may be in progress. These results are consistent with a model which posits that egg VERL is neutrally evolving, perhaps due to its repetitive structure, while sperm lysin is subjected to positive Darwinian selection to maintain efficient interaction of the two proteins during sperm competition.     

Crystal structure and subunit dynamics of the abalone sperm lysin dimer: egg envelopes dissociate dimers, the monomer is the active species

Lysin is a 16-kD acrosomal protein used by abalone spermatozoa to create a hole in the egg vitelline envelope (VE) by a nonenzymatic mechanism. The crystal structure of the lysin monomer is known at 1.9 A resolution. The surface of the molecule reveals two tracks of basic residues running the length of one surface of the molecule and a patch of solvent-exposed hydrophobic residues on the opposite surface. Here we report that lysin dimerizes via interaction of the hydrophobic patches of monomers. Triton X-100 dissociates the dimer. The crystal structure of the dimer is described at 2.75 A resolution. Fluorescence energy transfer experiments show that the dimer has an approximate KD of 1 microM and that monomers exchange rapidly between dimers. Addition of isolated egg VE dissociates dimers, implicating monomers as the active species in the dissolution reaction. This work represents the first step in the elucidation of the mechanism by which lysin enables abalone spermatozoa to create a hole in the egg envelope during fertilization.     

Interspecies chimeric sperm lysins identify regions mediating species-specific recognition of the abalone egg vitelline envelope.

Abalone sperm lysin is a nonenzymatic, 16-kDa protein that creates a hole in the egg vitelline envelope (VE) through which the sperm swims to fuse with the egg. The dissolution of isolated VE by lysin is species specific. Interspecies comparisons show that the most divergent region of lysin is the N-terminal segment of residues 1-12 which is always species-unique. The C-terminus and three internal segments are moderately variable between species, but not species unique. Analysis of nucleotide substitutions shows that lysin evolves rapidly by positive Darwinian selection, suggesting that there is adaptive value in altering its amino acid sequence. The results reported here, in which segments of lysin were exchanged between two species, prove by direct experimentation that the interspecies variable termini play major roles in the species-specific recognition between sperm lysin and the egg VE.     

Speciation genes in free-spawning marine invertebrates

Research on speciation of marine organisms has lagged behind that of terrestrial ones, but the study of the evolution of molecules involved in the adhesion of gametes in free-spawning invertebrates is an exception. Here I review the function, species-specificity, and molecular variation of loci coding for bindin in sea urchins, lysin in abalone and their egg receptors, in an effort to assess the degree to which they contribute to the emergence of reproductive isolation during the speciation process. Bindin is a protein that mediates binding of the sperm to the vitelline envelope (VE) of the egg and the fusion of the gametes' membranes, whereas lysin is a protein involved only in binding to the VE. Both of these molecules are important in species recognition by the gametes, but they rarely constitute absolute blocks to interspecific hybridization. Intraspecific polymorphism is high in bindin, but low in lysin. Polymorphism in bindin is maintained by frequency-dependent selection due to sexual conflict arising from the danger of polyspermy under high densities of sperm. Monomorphism in lysin is the result of purifying selection arising from the need for species recognition. Interspecific divergence in lysin is due to strong positive selection, and the same is true for bindin of four out of seven genera of sea urchins studied to date. The differences between the sea urchin genera in the strength of selection can only partially be explained by the hypothesis of reinforcement. The egg receptor for lysin (VERL) is a glycoprotein with 22 repeats, 20 of which have evolved neutrally and homogenized by concerted evolution, whereas the first two repeats are under positive selection. Selection on lysin has been generated by the need to track changes in VERL, permitted by the redundant structure of this molecule. Both lysin and bindin are important in reproductive isolation, probably had a role in speciation, but it is hard to determine whether they meet the strictest criteria of "speciation loci," defined as genes whose differentiation has caused speciation.     

The crystal structure of a fusagenic sperm protein reveals extreme surface properties

Sp18 is an 18 kDa protein that is released from abalone sperm during the acrosome reaction. It coats the acrosomal process where it is thought to mediate fusion between sperm and egg cell membranes. Sp18 is evolutionarily related to lysin, a 16 kDa abalone sperm protein that dissolves the vitelline envelope surrounding the egg. The two proteins were generated by gene duplication followed by rapid divergence by positive selection. Here, we present the crystal structure of green abalone sp18 resolved to 1.86 A. Sp18 is composed of a bundle of five alpha-helices with surface clusters of basic and hydrophobic residues, giving it a large dipole moment and making it extremely amphipathic. The large clusters of hydrophobic surface residues and domains of high positive electrostatic surface charge explain sp18's ability as a potent fusagen of liposomes. The overall fold of sp18 is similar to that of green abalone lysin; however, the surface features of the proteins are quite different, accounting for their different roles in fertilization. This is the first crystal structure of a protein implicated in sperm-egg fusion during animal fertilization.     

The high resolution crystal structure of green abalone sperm lysin: implications for species-specific binding of the egg receptor

Abalone sperm lysin is a 16 kDa acrosomal protein used by sperm to create a hole in the egg vitelline envelope. Lysins from seven California abalone exhibit species-specificity in binding to their egg receptor, and range in sequence identity from 63 % to 90 %. The crystal structure of the sperm lysin dimer from Haliotis fulgens (green abalone) has been determined to 1.71 A by multiple isomorphous replacement. Comparisons with the structure of the lysin dimer from Haliotis rufescens (red abalone) reveal a similar overall fold and conservation of features contributing to lysin's amphipathic character. The two structures do, however, exhibit differences in surface residues and electrostatics. A large clustering of non-conserved surface residues around the waist and clefts of the dimer, and differences in charged residues around these regions, indicate areas of the molecule which may be involved in species-specific egg recognition.     

Structural features of the abalone egg extracellular matrix and its role in gamete interaction during fertilization

Abalone eggs are surrounded by a complex extracellular coat that contains three distinct elements: the jelly layer, the vitelline envelope, and the egg surface coat. In this study we used light and electron microscopy to describe these three elements in the red abalone (Haliotis rufescens) and ascribe function to each based on their interactions with sperm. The jelly coat is a spongy matrix that lies at the outermost margin of the egg and consists of variably sized fibers. Sperm pass through this layer with their acrosomes intact and then go on to bind to the vitelline envelope. The vitelline envelope is a multilamellar fibrous layer that appears to trigger the acrosome reaction after sperm binding. Next, sperm release lysin from their acrosomal granules, a nonenzymatic protein that dissolves a hole in the vitelline envelope through which the sperm swims. Sperm then contact the egg surface coat, a network of uniformly sized filaments lying directly above the egg plasma membrane. This layer mediates attachment of sperm, via their acrosomal process, to the egg surface. © 1995 Wiley-Liss, Inc.     

Positive selection is a general phenomenon in the evolution of abalone sperm lysin

Lysin is a 16kDa acrosomal protein used by abalone sperm to create a hole in the egg vitelline envelope (VE). The interaction of lysin with the VE is species-selective and is one step in the multistep fertilization process that restricts heterospecific (cross-species) fertilization. For this reason, the evolution of lysin could play a role in establishing prezygotic reproductive isolation between species. Previously, we sequenced sperm lysin cDNAs from seven California abalone species and showed that positive Darwinian selection promotes their divergence. In this paper an additional 13 lysin sequences are presented representing species from Japan, Taiwan, Australia, New Zealand, South Africa, and Europe. The total of 20 sequences represents the most extensive analysis of a fertilization protein to date. The phylogenetic analysis divides the sequences into two major clades, one composed of species from the northern Pacific (California and Japan) and the other composed of species from other parts of the world. Analysis of nucleotide substitution demonstrates that positive selection is a general process in the evolution of this fertilization protein. Analysis of nucleotide and codon usage bias shows that neither parameter can account for the robust data supporting positive selection. The selection pressure responsible for the positive selection on lysin remains unknown.      

The Tegula tango: a coevolutionary dance of interacting, positively selected sperm and egg proteins

Reproductive proteins commonly show signs of rapid divergence driven by positive selection. The mechanisms driving these changes have remained ambiguous in part because interacting male and female proteins have rarely been examined. We isolate an egg protein the vitelline envelope receptor for lysin (VERL) from Tegula, a genus of free-spawning marine snails. Like VERL from abalone, Tegula VERL is a major component of the VE surrounding the egg, includes a conserved zona pellucida (ZP) domain at its C-terminus, and possesses a unique, negatively charged domain of about 150 amino acids implicated in interactions with the positively charged lysin. Unlike for abalone VERL, where this unique VERL domain occurs in a tandem array of 22 repeats, Tegula VERL has just one such domain. Interspecific comparisons show that both lysin and the VERL domain diverge via positive selection, whereas the ZP domain evolves neutrally. Rates of nonsynonymous substitution are correlated between lysin and the VERL domain, consistent with sexual antagonism, although lineage-specific effects, perhaps owing to different ecologies, may alter the relative evolutionary rates of sperm- and egg-borne proteins.