ADAMs与哺乳动物受精

ADAMs是近几年发现的一类具有多个结构区和广泛生物学功能的糖蛋白,它们在哺乳动物受精中的作用日益得到实验结果的支持,本文简要总结了近几年ADAMs在哺乳动物受精中作用的研究进展。     

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…     

哺乳动物卵子受精过程中糖蛋白的作用

哺乳动物卵子受精过程中糖蛋白的作用邹记兴（中国科学院南海海洋研究所广州５１０３０ｌ）闻仁龙（湖北省武汉市第三师范学校武汉４３０２００）本世纪５０年代以来,由于哺乳动物卵子体外培养系统的建立和不断完善,科学家们可以直接用哺乳动物的精卵为材料,对受精过程...     

哺乳动物受精的生物学

哺乳动物的受精(Mammalian Fertilization)是两性配子(精子和卵子)相结合而形成合子的过程,它标志着胚胎发育的开始,也即是一个新生命的起点。受精是生物学家饶有兴味的课题。因为它不仅涉及到一个理论问题,更重要的是当今节育和不育的世界性问题尚未解决,因此,受精的重要性是不言而喻的。当然,受精是一个极其复杂的生命现象,涉及到两性配子的发育和成熟、精子获能、顶体反应、精卵激活、精子     

哺乳动物卵母细胞成熟和受精中细胞骨架重组和作用

卵母细胞成熟和受精是动物生殖过程的核心环节。细胞骨架是遍布于卵母细胞胞质中的一种复杂的蛋白质纤维网络,研究表明,卵母细胞成熟和受精过程中伴随着广泛的胞质骨架重组。哺乳动物卵母细胞和早期胚胎中细胞骨架具有其独特的分布和功能,使卵母细胞和胚胎呈现出不同的变化特点。微丝、微管的分布变化与卵母细胞成熟和受精中遗传物质的重组密切相关。近年来,对哺乳动物不同物种间卵母细胞和胚胎中细胞骨架成分的研究取得了很大的进展,结合这些研究成果,对哺乳动物卵母细胞成熟和受精过程中细胞骨架的重组、分布和作用进行了介绍。同时,对多种信号转导途径参与卵母细胞成熟和受精中细胞骨架系统的调控也作了探讨。     

哺乳动物精子与卵子质膜粘附和融合的分子基础

精子与卵子质膜粘附并发生融合是哺乳动物完成受精过程所必需的步骤。近年来,学者们以现代分子生物学理论为基础,对参与精卵质膜粘附、融合过程的分子进行了研究,特别是精子表面的去整合素金属蛋白酶基因家族(ADAM)和卵子表面的整合素蛋白。本文通过对精子表面的受精素仅、受精素β、cyritestin,卵子表面的α6β1、CD9等蛋白分子的研究,揭示了这些分子对粘附、融合的重要作用,为提高受精率提供了重要的依据。     

受精环境对哺乳动物性别形成的影响

性别控制是人类很早就关心的研究领域, 许多重要的经济性状与性别有直接的关系。控制受精环境即可控制性别, 这种方法不需昂贵的仪器设备或者药品, 易实践, 可普遍应用, 其经济效益和社会效益难以估量。文章综述了受精环境对哺乳动物性别形成影响的研究进展。这些环境因素包括母体生殖道中精氨酸含量、胚胎发育过程中子宫内葡萄糖浓度、输精时卵母细胞成熟程度以及哺乳动物受孕时生殖激素的水平等方面, 为进一步开展性别控制研究积累一定的资料。     

精子功能相关的蛋白质调控受精过程的研究进展

哺乳动物的受精过程涉及到精子一系列的功能活动,如精子在雌性生殖道的运行、精子的超活化与获能、顶体反应以及精卵融合等。在精子经历的这一系列过程中,精子功能相关的蛋白质发挥着不可或缺的作用,这些蛋白分子的正常与否与雄性个体的繁殖力高低密切相关,因此精子功能相关的蛋白质能够作为评定哺乳动物精液受精能力的生物标记。文章主要对哺乳动物精子功能相关的蛋白质进行了综述,以阐述相关蛋白分子对精子运动活力、精子获能、顶体反应、透明带穿入和精卵融合等方面的重要作用以及这些蛋白分子在家畜遗传改良上的潜在应用。     

ADAMs与生长发育(英文)

ADAMs是近几年发现和鉴定的一类具有多个结构域和广泛生物学功能的细胞表面糖蛋白 ,由信号肽区、前调控区、金属蛋白水解酶区、去整合蛋白区、富半胱氨酸区、表皮生长因子区、跨膜区和胞质区组成 ,已发现 3 0多种成员。它们在性细胞发生、受精、胚胎发育、细胞融合、器官形成、细胞分化等方面起重要作用。本文重点介绍了ADAM1 0 Kuz在神经发育过程中的信号传导和蛋白水解酶作用及ADAM1 7 TACE、ADAMTS在小鼠胚胎发育过程中对眼、肾、肾上腺、生殖等器官结构、功能的作用 ;另外 ,还对ADAM1 2 meltrinα促进肌细胞融合、分化、MIG 1 7介导细胞迁移等多种ADAMs在生长发育方面的研究作了简要介绍     

ADAMs与生长发育

ADAMs是近几年发现和鉴定的一类具有多个结构域和广泛生物学功能的细胞表面糖蛋白,由信号肽区、前调控区、金属蛋白水解酶区、去整合蛋白区、富半胱氨酸区、表皮生长因子区、跨膜区和细胞质区组成,已发现30多种成员。它们在性细胞发生、受精、胚胎发育、细胞融合、器官形成、细胞分化等方面起重要作用。本文重点介绍了ADAM10／Kuz在神经发育过程中的信号传导和蛋白水解酶作用及ADAM17／TACE、ADAMTS在小鼠胚胎发育过程中对眼、肾、肾上腺、生殖等器官结构、功能的作用;另外,还对ADAM12／meltrin α促进肥细胞融合、分化、MIG－17介导细胞迁移等多种ADAMs在生长发育方面的研究作了简要介绍。     

Preventing polyspermy in mammalian eggs—Contributions of the membrane block and other mechanisms

The egg's blocks to polyspermy (fertilization of an egg by more than one sperm) were originally identified in marine and aquatic species with external fertilization, but polyspermy matters in mammalian reproduction too. Embryonic triploidy is a noteworthy event associated with pregnancy complications and loss. Polyspermy is a major cause of triploidy with up to 80% of triploid conceptuses being the result of dispermic fertilization. The mammalian female reproductive tract regulates the number of sperm that reach the site of fertilization, but mammals also utilize egg‐based blocks to polyspermy. The egg‐based blocks occur on the mammalian egg coat (the zona pellucida) and the egg plasma membrane, with apparent variation between different mammalian species regarding the extent to which one or both are used. The zona pellucida block to polyspermy has some similarities to the slow block in water‐dwelling species, but the mammalian membrane block to polyspermy differs substantially from the fast electrical block that has been characterized in marine and aquatic species. This review discusses what is known about the incidence of polyspermy in mammals and about the mammalian membrane block to polyspermy, as well as notes some lesser‐characterized potential mechanisms contributing to polyspermy prevention in mammals.     

RECENT PROGRESS IN THE STUDY OF EARLY EVENTS IN MAMMALIAN FERTILIZATION*

During the past 25 years, great advances have been made in understanding the physiology, morphology and biochemistry of fertilization in invertebrate animal species. In contrast to this situation, there is a paucity of knowledge pertaining to mammalian fertilization. Major areas in which information is lacking are the nature of changes undergone by spermatozoa in preparation for fertilization, and the mechanisms involved in sperm penetration of the egg investments. The present state of knowledge of these events is outlined, and the weaknesses of some current concepts are evaluated. Fertilization of mammalian eggs in vitro seems an attractive method for studying gamete interaction, but experience has shown that numerous problems are associated with this technique. As a result, the information on mammalian fertilization that has been derived from studies conducted in vitro has fallen considerably short of expectations; some factors contributing to this discrepancy are described. Recent findings concerning the regulation of sperm motility and fertilizing ability seem to have considerable significance for mammalian fertilization in vivo and in vitro. These findings have been utilized to refine existing procedures; fertilization of hamster eggs in vitro has now been accomplished in the presence of numbers of spermatozoa comparable to those believed to be present at the site and time of fertilization in vivo. It is anticipated that this improved technique, by more closely approximating the physiological situation, will substantially assist the derivation of useful information from in vitro fertilization studies.     

Pervasive adaptive evolution in mammalian fertilization proteins

Mammalian fertilization exhibits species specificity, and the proteins mediating sperm-egg interactions evolve rapidly between species. In this study, we demonstrate that the evolution of seven genes involved in mammalian fertilization is promoted by positive Darwinian selection by using likelihood ratio tests (LRTs). Several of these proteins are sperm proteins that have been implicated in binding the mammalian egg coat zona pellucida glycoproteins, which were shown previously to be subjected to positive selection. Taken together, these represent the major candidates involved in mammalian fertilization, indicating positive selection is pervasive amongst mammalian reproductive proteins. A new LRT is implemented to determine if the d(N)/d(S) ratio is significantly greater than one. This is a more refined test of positive selection than the previous LRTs which only identified if there was a class of sites with a d(N)/d(S) ratio >1 but did not test if that ratio was significantly greater than one.     

Peptides corresponding to the epidermal growth factor-like domain of mouse fertilin: synthesis and biological activity

A key step leading to fertilization is the binding of sperm to the egg plasma membrane. When a mammalian sperm reaches the egg plasma membrane, fertilin, an extracellular sperm membrane protein, is believed to bind to an egg plasma membrane receptor mediating fusion. Fertilin is composed of two subunits, and each subunit contains several domains, i.e., metalloprotease, disintegrin, epidermal growth factor (EGF)-like and fusion domains. This investigation examined the role of the EGF-like domains of mouse fertilin alpha and fertilin beta. Peptides corresponding to the N-terminal subdomain, containing four cysteines, and the C-terminal subdomain, containing two cysteines, were synthesized by solid-phase synthesis methods. Disulfide bonds were formed regioselectively according to the canonical EGF-like disulfide pattern. The activity of these peptides and their linear counterparts were tested for activity in a mouse in vitro fertilization assay. One peptide, 4a, corresponding to the cystine-constrained N-terminal subdomain of fertilin beta, had an activating effect on fertilization. The fertilization rate (number of eggs fertilized), fertilization index (number of sperm fused per egg), and level of polyspermy (three or more sperm fused per egg) increased in the presence of 500 microM 4a (12, 56, and 190%, respectively). Its linear counterpart, 4b, had no effect on in vitro fertilization. These data suggest that the EGF-like domain of fertilin beta has a function in sperm-egg binding and fusion. Previously, it has been shown that the fertilin beta disintegrin domain has a role in sperm-egg binding. Considered together, these studies suggest that fertilin is a modular, multidomain protein with more than one mechanism of action. This modularity may be used to design inhibitors of fertilin-receptor interactions that have high specificities for the fertilization process.     

Ca(2+) oscillations induced by a cytosolic sperm protein factor are mediated by a maternal machinery that functions only once in mammalian eggs

At fertilization in mammals, the sperm activates the egg by inducing a series of oscillations in the intracellular free Ca(2+) concentration. There is evidence showing that this oscillatory event is triggered by a sperm-derived protein factor which diffuses into egg cytoplasm after gamete membrane fusion. At present the identity of this factor and its precise mechanism of action is unknown. Here, we studied the specificity of action of the sperm factor in triggering Ca(2+) oscillations in mammalian eggs. In doing so, we examined the patterns of Ca(2+) signaling in mouse eggs, zygotes, parthenogenetic eggs and maturing oocytes following the stimulation of bovine sperm extracts which contain the sperm factor. It is observed that the sperm factor could induce Ca(2+) oscillations in metaphase eggs, maturing oocytes and parthenogenetically activated eggs but not in the zygotes. We present evidence that Ca(2+) oscillations induced by the sperm factor require a maternal machinery. This machinery functions only once in mammalian oocytes and eggs, and is inactivated by sperm-derived components but not by parthenogenetic activation. In addition, it is found that neither InsP(3) receptor sensitivity to InsP(3) nor Ca(2+) pool size are the determinants that cause the fertilized egg to lose its ability to generate sperm-factor-induced Ca(2+) oscillations at metaphase. In conclusion, our study suggests that the orderly sequence of Ca(2+) oscillations in mammalian eggs at fertilization is critically dependent upon the presence of a functional maternal machinery that determines whether the sperm-factor-induced Ca(2+) oscillations can persist.     

Profile of a mammalian sperm receptor

Complementary molecules on the surface of eggs and sperm are responsible for species-specific interactions between gametes during fertilization in both plants and animals. In this essay, several aspects of current research on the mouse egg receptor for sperm, a zona pellucida glycoprotein called ZP3, are addressed. These include the structure, synthesis, and functions of the sperm receptor during oogenesis and fertilization in mice. Several conclusions are drawn from available information. These include (I) ZP3 is a member of a unique class of glycoproteins found exclusively in the extracellular coat (zona pellucida) of mammalian eggs. (II) ZP3 gene expression is an example of oocyte-specific and, therefore, sex-specific gene expression during mammalian development. (III) ZP3 is a structural glycoprotein involved in assembly of the egg extracellular coat during mammalian oogenesis. (IV) ZP3 is a sperm receptor involved in carbohydrate-mediated gamete recognition and adhesion during mammalian fertilization. (V) ZP3 is an inducer of sperm exocytosis (acrosome reaction) during mammalian fertilization. (VI) ZP3 participates in the secondary block to polyspermy following fertilization in mammals. (VII) The extracellular coat of other mammalian eggs contains a glycoprotein that is functionally analogous to mouse ZP3. The unique nature, highly restricted expression, and multiple roles of ZP3 during mammalian development make this glycoprotein a particularly attractive subject for investigation at both the cellular and molecular levels.     

Mechanism of Fertilization: A Modern View

Despite numerous studies on mammalian fertilization, the mechanisms of fertilization—including the timing of acrosome reaction—remain largely unknown; more accurately described, the classical theory built upon years of layered experimental data is being challenged by recent conflicting evidence provided by gene-manipulated animals. Although in vitro fertilization remains our central research tool, the classical theory’s decline reminds us of the importance of in vivo observations. Here, I describe the essential roles of gene-manipulated animals in elucidating the mechanism of fertilization and the pitfalls of in vitro fertilization studies trapping many researchers.     

Mitochondrial sheath movement and detachment in mammalian,but not nonmammalian,sperm induced by disulfide bond reduction

The successful completion of the fertilization process requires the properly choreographed unsheathing of the tightly packaged sperm once it has been fully incorporated into the egg's cytoplasm. The nuclear and accessory structures of mammalian sperm become stabilized by disulfide bonds (S-S) during epididymal maturation. This stabilization is reversed during fertilization by the reduction of S-S cross-linking, but little is known about the effect of S-S reduction on individual disulfide-hardened structures such as the sperm's connecting piece, fibrous sheath, and mitochondria. Here, we demonstrate the action of the S-S-reducing environment on the mitochondrial sheath of mammalian sperm, visualized by the vital fluorescent probe Mito Tracker and by electron microscopy. In both human and bull sperm, mitochondria form a compact helix (mitochondrial sheath) wrapped around the midpiece and connecting piece that can be fluorescently labelled by a short incubation with 100 mM Mito-Tracker. Exposure of bull sperm to 0.1–10 mM dithiothreitol (DTT; a disulfide bond-reducing agent) induced a time and dose-dependent sliding of the mitochondrial sheath down the axoneme, accompanied by the excision of the sperm tail and decondensation of the sperm nucleus. Increasing the concentration of DTT to 100 mM accelerated mitochondrial movement, causing a completed stripping of sperm mitochondria and partial disassembly of the connecting piece. Likewise, human sperm responded to DTT treatment by the sliding or removal of the mitochondrial sheath and decondensation of the sperm chromatin. These events were not observed in the sperm of lower vertebrates and invertebrates (Xenopus laevis and Lytechinus pictus, respectively) exposed to an excess of DTT. Thus the sensitivity of sperm mitochondria to the S-S reducing environment seems to be an exclusive feature of mammalian sperm. The movement of sperm mitochondria induced by S-S reduction may be an initial critical step in the disassembly of the mammalian sperm tail during fertilization. Mol. Reprod. Dev. 47:79–86, 1997. © 1997 Wiley-Liss, Inc.     

PKC signaling at fertilization in mammalian eggs

Protein kinase C (PKC) has been proposed to regulate major egg activation events during mammalian fertilization. Most of the evidence supporting this assumption has first been obtained using pharmacological activation and inhibition of the kinase, while egg activation was assessed by checking for exocytosis of the cortical granules, extrusion of the second polar body and formation of pronuclei. However, results have been inconclusive and sometimes contradictory regarding the exact role of PKC in regulating egg activation events. The PKC family is composed of various isotypes, which differ in their modular structures and regulatory properties. Hence the need to re-examine the roles of egg PKCs more specifically. Mammalian eggs express many PKC isotypes, the roles of which have been investigated using immunodetection, isotype-specific inhibition and, more recently, live imaging of fluorescent chimaeras. Here, I review the recent development of PKC research in mammalian fertilization and the evidence for a specific role for certain PKC isotypes in fertilization-induced egg activation.