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。     

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。     

精子发生过程中的相关基因

在哺乳动物精子发生过程中, 原生殖细胞发育成为精原细胞, 再发育为精母细胞, 精母细胞经过两次减数分裂成为圆形精细胞, 这些圆形精细胞经过细胞变态形成精子。精子发生过程经历了复杂的细胞分化阶段, 这一阶段受许多因素的调控作用, 其中生精细胞内的基因调节起着决定作用。精子发生中的重要基因与一系列精子发生过程中阶段性的细胞事件密切相关, 例如减数分裂重组、联会丝复合物的形成、姊妹染色体的结合、减数分裂后精子的变态以及减数分裂周期中的关键点和必需因子等。生精细胞许多特异基因的阶段特异性表达, 参与了精子发生这一特殊的细胞分化过程。近年来随着基因克隆、表达和功能研究技术的发展和应用, 发现了许多与精子发生相关的基因, 而且有的被证明在精子发生过程中具有重要作用。文章较全面综述了这一研究领域的一些进展, 着重讨论了与精子发生相关的周期蛋白基因、原癌基因、无精子因子基因、细胞骨架基因、热休克基因、核蛋白转型基因、中心体蛋白基因和细胞凋亡相关基因等。     

精子磷酸化蛋白质组学研究应用

蛋白质磷酸化是生物体中广泛存在的翻译后修饰方式,参与多种过程的调节。精子是高度分化的特殊细胞,不具有转录活性,主要依赖于蛋白质的磷酸化完成精子成熟、分化和受精等过程。因此,对于精子磷酸化蛋白质组学的研究有助于进一步了解精子发生、精子获能、超激活以及精卵识别等过程的调控机制。本文简要综述了精子磷酸化蛋白质组学的研究方法及磷酸化蛋白质组学在精子中的应用,为精子磷酸化蛋白质组学在实际科研应用中提供了理论参考。     

体外受精-胚胎移植中完全受精失败的原因分析

受精是生命起源至关重要的一个步骤。在辅助生殖的过程中,完全受精失败发生具有其复杂性和不可预见性。受精失败常伴随着一些胞间调控机制异常,其中,可能阻滞在与精子穿越卵冠丘复合体、精子-透明带结合/穿透、精子-卵膜结合、卵子激活、精子去浓缩或原核形成等任一阶段。通过卵胞浆内单精子注射可以避免大部分受精失败现象,但某些患者仍无法成功受精,即使采用辅助人工激活也无法完全避免其发生。对于在辅助生殖过程中完全受精失败患者,结合其卵子成熟情况、精子质量及相关检测结果,在后续周期调整临床方案可有效避免受精失败的再次发生。     

傅氏凤尾蕨精子发生超微结构的研究

超微结构研究显示傅氏凤尾蕨（Pteris fauriei Hieron）精子发生过程包括生毛体、多层结构和鞭毛等运动细胞器重新发生,环状线粒体形成,核塑形等过程,最后形成一个螺旋形的游动精子,这与其他真蕨类精子发生过程相似。本研究观察到的一些新现象包括：精细胞在分化早期呈极性,细胞核位于精细胞的近极端,生毛体、线粒体和质体等细胞器主要分布远极端;在生毛体分化早期,可见大量微管从其发出,其周围线粒体丰富;基体分化经历了前中心粒、中心粒和基体3个阶段,它们的内部结构不同;研究表明生毛体内的不定形物质是微管组织者,多层结构、附属微管带及鞭毛等细胞器均由不定形物质分化形成;精细胞在分化过程中产生了丰富的膜结构,它们可能为精核塑形提供原料。本研究报道了傅氏凤尾蕨精细胞分化的一些细节,这有助于进一步揭示蕨类植物精子发生的细胞学机制。     

精子发生转录调控机制的研究进展

精子发生过程中的转录调控是由一系列基因表达和调控事件组成的复杂过程,影响精子的形成、质量和功能。转录调控过程介导与精子形成密切相关的基因,包括精子特异性基因、组蛋白基因和其他转录因子的基因表达。这些基因的表达和沉默受到转录因子、表观遗传修饰和非编码RNA等多种机制的调控。此外,转录调控在精子发生的不同阶段起着不同的作用,包括精原干细胞的自我更新和分化、精母细胞的减数分裂和精子细胞的变形成熟。深入理解精子发生中的转录调控机制对于研究精子形成的生物学过程、解析生育障碍的病理机制以及开发生育问题相关的治疗方法具有重要的意义。     

核糖体的翻译调控及其在精子发生中的研究进展

蛋白质合成过程是基因表达不可或缺的关键步骤,将信使RNA(mRNA)中编码的遗传信息转化为特定的蛋白质。这个过程在各种生物中都具有高度的保守性,是细胞生长、发育、繁殖和适应环境变化的基础。核糖体作为蛋白质合成的“执行器”,在这个复杂而精密的过程中扮演着不可或缺的角色。在精子的形成过程中蛋白质的合成及其精准调控对于正常精子发生至关重要。这种调控的精密性使得精子能够在发育过程中经历形态和功能的变化,从而最终成熟为能够完成受精任务的精子。该文将深入探讨核糖体的组成、功能、在翻译过程中的调控机制,包括精子发生过程中的翻译调控作用,阐述其在生殖生物学领域的重要意义。     

类c-kit原癌蛋白在多伊棺头蟋胚后精子发生中的表达和定位

为了了解类c-kit原癌蛋白在多伊棺头蟋Loxoblemmus doenitzi Stein胚后精子发生中的表达、定位及可能的调控作用,采用常规免疫组织化学方法进行了相关研究。结果表明：处于减数分裂中期Ⅰ至末期Ⅱ的初级精母细胞的细胞膜上有类c-kit原癌蛋白阳性颗粒;精巢或受精囊内成熟精子头部也具有类c-kit原癌蛋白阳性颗粒。结果反映了类c-kit蛋白对于维持动物精子发生过程中减数分裂、精子成熟及受精能力具有特殊功能。     

哺乳动物精子磷酸化蛋白质组学研究进展

蛋白质的表达、修饰及相互作用的研究已成为后基因组学时代蛋白质组学中的重要内容。蛋白质磷酸化和去磷酸化作为最普遍的翻译后修饰之一,是精子细胞信号转导和酶调控、表达的主要分子机制,亦是精子、卵细胞信号识别及完成受精作用的关键环节。对精子磷酸化蛋白功能的研究有助于深入理解精子的获能、超激活运动的维持、发生顶体反应及精卵结合等受精过程的分子调控机理。对哺乳动物精子磷酸化蛋白质组学的研究进展,包括动物精子磷酸化蛋白质组学研究的技术方法、磷酸化蛋白质种类的鉴定、定量及其功能分析进行了综述,为进一步发掘与受精相关的重要生物标志物,揭示精子发育、繁殖潜能变化及受精分子机理奠定基础。     

Abnormal spermatogenesis at low temperatures in the Japanese red-bellied newt,Cynops pyrrhogaster: possible biological significance of the cessation of spermatocytogenesis

In newt testis, spermatocytes never appear during winter, because secondary spermatogonia die by apoptosis just before meiosis. In the current study, we examined the effect of low temperatures on spermatogenesis. Incubation of newts at low temperatures (8, 12, 15 degrees C) induced defects in spermatogenesis in a temperature-dependent manner. At 8 degrees C, multinucleated giant cells (MGCs) were observed in spermatocytes and spermatogenesis never proceeded beyond meiosis. Although spermatocytes completed meiotic divisions at 12 degrees C, severe cell death was observed in the spermatids. At 15 degrees C both normal and abnormal spermiogenesis were observed. Under these conditions, impaired meiotic synapsis/recombination and down-regulation of the expression of the DMC1 protein, which play pivotal roles in meiotic pairing in eukaryotes, were also observed. Furthermore, to examine the quality of the sperm produced at low temperature for supporting development, artificial insemination was performed. The eggs inseminated with spermatozoa derived from newts kept at 15 degrees C demonstrated a restricted developmental capacity, even though these spermatozoa had an equal capacity for carrying out fertilization to those kept at 22 degrees C. These results suggest that meiosis at low temperatures cause the production of abnormal spermatozoa. Conservation and the significance of this phenomenon in poikilothermic vertebrates living in the temperate zones are also discussed.     

Sperm of Doradidae (Teleostei: Siluriformes)

Spermatic characteristics were studied in 10 species representing several distinct groups within the catfish family Doradidae. Interestingly, different types of spermatogenesis, spermiogenesis and spermatozoa are correlated with intrafamilial groups previously proposed for Doradidae. Semi-cystic spermatogenesis, modified Type III spermiogenesis, and biflagellate sperm appear to be unique within Doradidae to the subfamily Astrodoradinae. Other doradid species have sperm with a single flagellum, cystic spermatogenesis, and spermiogenesis of Type I (Pterodoras granulosus, Rhinodoras dorbignyi), Type I modified (Oxydoras kneri), or Type III (Trachydoras paraguayensis). Doradids have an external mode of fertilization, and share a few spermatic characteristics, such as cystic spermatogenesis, Type I spermiogenesis and uniflagellate sperm, with its sister group Auchenipteridae, a family exhibiting sperm modifications associated with insemination and internal fertilization. Semi-cystic spermatogenesis and biflagellate spermatozoa are also found in Aspredinidae, and corroborate recent proposals that Aspredinidae and Doradoidea (Doradidae + Auchenipteridae) are sister groups and that Astrodoradinae occupies a basal position within Doradidae. The co-occurrence in various catfish families of semi-cystic spermatogenesis and either biflagellate spermatozoa (Aspredinidae, Cetopsidae, Doradidae, Malapturidae, Nematogenyidae) or uniflagellate sperm with two axonemes (Ariidae) reinforces the suggestion that such characteristics are correlated. Semi-cystic spermatogenesis and biflagellate sperm may represent ancestral conditions for Loricarioidei and Siluroidei of Siluriformes as they occur in putatively basal members of each suborder, Nematogenyidae and Cetopsidae, respectively. However, if semi-cystic spermatogenesis and biflagellate sperm are ancestral for Siluriformes, cystic spermatogenesis and uniflagellate sperm have arisen independently in multiple lineages including Diplomystidae, sister group to Siluroidei.     

Spermiogenesis initiation in Caenorhabditis elegans involves a casein kinase 1 encoded by the spe-6 gene

Immature spermatids from Caenorhabditis elegans are stimulated by an external activation signal to reorganize their membranes and cytoskeleton to form crawling spermatozoa. This rapid maturation, termed spermiogenesis, occurs without any new gene expression. To better understand this signal transduction pathway, we isolated suppressors of a mutation in the spe-27 gene, which is part of the pathway. The suppressors bypass the requirement for spe-27, as well as three other genes that act in this pathway, spe-8, spe-12, and spe-29. Eighteen of the suppressor mutations are new alleles of spe-6, a previously identified gene required for an early stage of spermatogenesis. The original spe-6 mutations are loss-of-function alleles that prevent major sperm protein (MSP) assembly in the fibrous bodies of spermatocytes and arrest development in meiosis. We have isolated the spe-6 gene and find that it encodes a predicted protein-serine/threonine kinase in the casein kinase 1 family. The suppressor mutations appear to be reduction-of-function alleles. We propose a model whereby SPE-6, in addition to its early role in spermatocyte development, inhibits spermiogenesis until the activation signal is received. The activation signal is transduced through SPE-8, SPE-12, SPE-27, and SPE-29 to relieve SPE-6 repression, thus triggering the formation of crawling spermatozoa.     

Developmental Genetics of Chromosome I Spermatogenesis-Defective Mutants in the Nematode Caenorhabditis Elegans

Mutations affecting Caenorhabditis elegans spermatogenesis can be used to dissect the processes of meiosis and spermatozoan morphological maturation. We have obtained 23 new chromosome I mutations that affect spermatogenesis (spe mutations). These mutations, together with six previously described mutations, identify 11 complementation groups, of which six are defined by multiple alleles. These spe mutations are all recessive and cause normally self-fertile hermaphrodites to produce unfertilized oocytes that can be fertilized by wild-type male sperm. Five chromosome I mutation/deficiency heterozygotes have similar phenotypes to the homozygote showing that the probable null phenotype of these genes is defective sperm. Spermatogenesis is disrupted at different steps by mutations in these genes. The maturation of 1 degree spermatocytes is disrupted by mutations in spe-4 and spe-5. Spermatids from spe-8 and spe-12 mutants develop into normal spermatozoa in males, but not in hermaphrodites. fer-6 spermatids are abnormal, and fer-1 spermatids look normal but subsequently become abnormal spermatozoa. Mutations in five genes (fer-7, spe-9, spe-11, spe-13 and spe-15) allow formation of normal looking motile spermatozoa that appear to be defective in either sperm-spermathecal or sperm-oocyte interactions.     

Mammalian sperm acrosome: formation, contents, and function

Sperm-egg interaction is a carbohydrate-mediated species-specific event which initiates a signal transduction cascade resulting in the exocytosis of sperm acrosomal contents (i.e., the acrosome reaction). This step is believed to be a prerequisite which enables the acrosome-reacted spermatozoa to penetrate the zona pellucida (ZP) and fertilize the egg. Successful fertilization in the mouse and several other species, including man, involves several sequential steps. These are (1) sperm capacitation in the female genital tract; (2) binding of capacitated spermatozoa to the egg's extracellular coat, the ZP; (3) induction of acrosome reaction (i.e., sperm activation); (4) penetration of the ZP; and (5) fusion of spermatozoon with the egg vitelline membrane. This minireview focuses on the most important aspects of the sperm acrosome, from its formation during sperm development in the testis (spermatogenesis) to its modification in the epididymis and function following sperm-egg interaction. Special emphasis has been given to spermatogenesis, a complex process involving multiple molecular events during mitotic cell division, meiosis, and the process of spermiogenesis. The last event is the final phase when a nondividing round spermatid is transformed into the complex structure of the spermatozoon containing a well-developed acrosome. Our intention is also to briefly discuss the functional significance of the contents of the sperm acrosome during fertilization. It is important to mention that only the carbohydrate-recognizing receptor molecules (glycohydrolases, glycosyltransferases, and/or lectin-like molecules) present on the surface of capacitated spermatozoa are capable of binding to their complementary glycan chains on the ZP. The species-specific binding event starts a calcium-dependent signal transduction pathway resulting in sperm activation. The hydrolytic and proteolytic enzymes released at the site of sperm-zona interaction along with the enhanced thrust of the hyperactivated beat pattern of the bound spermatozoon, are important factors in regulating the penetration of the zona-intact egg.     

Clustered organization of reproductive genes in the C. elegans genome

Defining the forces that sculpt genome organization is fundamental for understanding the origin, persistence, and diversification of species. The genomic sequences of the nematodes Caenorhabditis elegans and Caenorhabditis briggsae provide an excellent opportunity to explore the dynamics of chromosome evolution. Extensive chromosomal rearrangement has accompanied divergence from their common ancestor, an event occurring roughly 100 million years ago (Mya); yet, morphologically, these species are nearly indistinguishable and both reproduce primarily by self-fertilization. Here, we show that genes expressed during spermatogenesis (sperm genes) are nonrandomly distributed across the C. elegans genome into three large clusters located on two autosomes. In addition to sperm genes, these chromosomal regions are enriched for genes involved in the hermaphrodite sperm/oocyte switch and in the reception of sperm signals that control fertilization. Most loci are present in single copy, suggesting that cluster formation is largely due to gene aggregation and not to tandem duplication. Comparative mapping indicates that the C. briggsae genome differs dramatically from the C. elegans genome in clustering. Because clustered genes have a direct role in reproduction and thus fitness, their aggregated pattern might have been shaped by natural selection, perhaps as hermaphroditism evolved.     

Haprin‐deficient spermatozoa are incapable of in vitro fertilization

Haprin (TRIM36) is a ubiquitin‐protein ligase that mediates ubiquitination and subsequent proteasomal degradation of target proteins. It is expressed in the testes in both mice and humans and is thought to be involved in spermiogenesis, the acrosome reaction, and fertilization. However, the functional role of Haprin is poorly understood. The aim of this study was to investigate the physiological role of Haprin in fertility. Homozygous haprin‐deficient mice were generated and these mice, and their spermatozoa, were analyzed to detect morphological and fertility‐related abnormalities. In these models, normal spermatogenesis was observed but sperm quality was reduced with haprin‐deficient mice having poorer sperm morphology and motility than wild‐type mice. Interestingly, haprin‐deficient mice showed normal in vivo fertility but could not fertilize oocytes under standard in vitro fertilization conditions. In conclusion, this study demonstrated that Haprin deficiency causes morphological abnormalities in spermatozoa, indicating that Haprin is involved in spermiogenesis.