抑制植物减数分裂重组的分子机理

减数分裂重组不仅保证了真核生物有性生殖过程中染色体数量的稳定,还通过父母亲本间遗传物质的互换在后代中产生遗传变异。因此,减数分裂重组是遗传多样性形成的重要途径,也是生物多样性和物种进化的主要动力。在绝大多数真核生物中,不管染色体数目的多少或基因组的大小,减数分裂重组的形成都受到严格的调控,但抑制减数分裂重组的分子机理目前仍不清楚。近年来,通过正向遗传学筛选鉴定出多个减数分裂重组抑制基因,揭示了抑制基因的功能和调控途径。本文基于拟南芥中减数分裂重组抑制基因的研究现状,综述了植物减数分裂重组抑制基因研究取得的突破性进展,并结合基因功能与其调控网络阐述了抑制植物减数分裂重组的分子机理。     

尼罗罗非鱼spo11基因的克隆表达及RU486处理对其表达的影响

正Spol1[SPOl1 meiotic protein covalently bound to DSB homolog(S.cerevisiae)]是减数分裂染色体重组过程中的重要蛋白,参与DNA双链断裂复合物(Double-Strand breaks,DSBs)的形成。目前已经从几种脊椎动物中克隆出了spol1基因,表明Spol1可能在所有真核生物减数分裂过程中都具有保守的功能[1,2]。最新研究表明,日本鳗鲡(Anguilla japonica)spol1基因仅在精子发生过程前期的精母细胞有表达,而在卵黄发生早期却没有检测到spol1的表达[2]。尽管研究者们普遍认为spol1是检测减数分裂的分子标记,但该基因在硬骨鱼类的表达模式并非完全保守,也未见关于spol1在硬骨鱼类个体发生过程     

上海辰山植物园植物抗逆与分子进化研究组科研助理招聘公告

<正>上海辰山植物园(中国科学院上海辰山植物科学研究中心)植物抗逆与分子进化研究组主要从事研究从单细胞真核生物到多细胞高等植物在进化过程中保守的应对多重非生物胁迫的响应、信号转导和耐受机理(聚焦MAPK信号传导途径)。发掘和收集极端生境植物基因资源(主要集中禾本科植物),利用抗多重非生物胁迫基因的单细胞筛选平台,筛选在进化过程中保守的多重抗逆基因,建立遗传转化研究体系,并     

纤毛虫分子系统发育学的研究进展

在回顾纤毛虫分子系统发育学产生发展历史的基础上,介绍了随着20年中RFLP、RAPD和DNA序列分析等分子生物学技术作为该学科的主要研究方法在种群遗传多样性与进化、种上阶元系统发育学两方面取得的研究成果和近期研究进展,最后在探讨纤毛虫分子系统发育学存在的一些问题和解决方法的同时,预测了纤毛虫分子系统发育学今后将极大地推动真核生物的起源与进化,内共生等重要生物进化问题的研究。     

浮萍棘尾虫Adss基因克隆及表达载体构建

为研究腺苷酸基琥珀酸合成酶(Adenylosuccinate synthase, 简称Adss)在原生动物中的作用, 对浮萍棘尾虫(Stylonychia lemnae)腺苷酸基琥珀酸合成酶Adss基因进行PCR克隆, 获得全长为1396 bp左右的序列, 其编码458个氨基酸, 保守结构域含有一个P-loop NTPase结构域, 蛋白结构预测Adss蛋白是由α-螺旋、β-折叠和无规卷曲组成的复杂结构。多重序列比对和系统进化分析显示浮萍棘尾虫Adss蛋白与第四双小核草履虫、多子小瓜虫和嗜热四膜虫等纤毛虫同源性较高。通过克隆浮萍棘尾虫Adss基因的启动子序列, 并采用增强型绿色荧光蛋白EGFP作为报告基因, 构建了启动子序列调控的表达载体pEGFP-N1-Adss, 通过转染细胞确定浮萍棘尾虫Adss蛋白定位于细胞质中。文章报道了原生动物纤毛虫Adss基因, 证实浮萍棘尾虫Adss蛋白属于典型的真核生物Adss, 为进一步揭示Adss在单细胞真核生物中的作用机制提供了新的参考。     

雌核发育二倍体鲫鲤Dmc1基因的全长cDNA克隆及表达分析

Dmc1（disrupted meiotic cDNA）基因是一个在减数分裂前期Ⅰ表达的特异基因,其产物是减数分裂前期Ⅰ同源染色体配对所必需的。根据据酵母菌、小鼠以及人的DMC1中保守的氨基酸基序设计简并引物,PCR扩增克隆获得了第四代雌核发育二倍体鲫鲤（G4）Dmc1基因部分cDNA序列。在此基础上,通过RACE获得了G4Dmc1基因全长cDNA序列,长度为1369bp,其中开放阅读框为1029bp,编码含342个氨基酸的蛋白质。同时,系统进化分析表明,在进化过程中Dmc1基因在鱼类中保持着高度保守的进化特征。RT-PCR结果表明,Dmc1基因只在G4性腺中表达,在其他组织中不表达。通过实时荧光定量PCR,对Dmc1基因在G4和普通鲤鱼的早期卵巢的表达进行分析,发现G4表达比鲤鱼高。由此可见,雌核发育二倍体鲫鲤Dmc1基因也是减数分裂特异基因,而且其高表达暗示雌核发育二倍体鲫鲤具有正常的减数分裂过程并且其早期性腺存在着多倍体卵原细胞。     

植物减数分裂同源染色体重组的分子机理

减数分裂是真核生物有性生殖过程中性母细胞成熟时所进行的特殊细胞分裂方式.在减数分裂过程中,同源染色体间需发生一系列有规律的重要事件,包括同源染色体配对、联会、重组、分离等,这些事件被证明是由许多遗传网络精密调控的.尽管许多调控减数分裂过程的基因已经被克隆,但减数分裂同源重组的分子机理仍不太清楚.植物是进行减数分裂研究的理想材料,近年来随着多种模式植物基因组序列测定的完成,大大加速了植物减数分裂相关基因的鉴定与功能研究.本文以拟南芥和水稻为主要对象,综述了植物减数分裂同源重组分子机理研究取得的一些重要进展,着重分析已鉴定同源重组相关蛋白的生物学功能.     

转录中介体复合物(Mediator complex)调控茉莉酸信号途径的新机制

转录中介体(Mediator)是由多个在进化上高度保守的亚基组成的蛋白复合物。在基因转录过程中,转录中介体分别与基因特异的转录因子和RNA聚合酶II相互作用,广泛参与二者之间的信息传递,被称为真核生物基因转录的中央控制器。在植物激素信号转导研究中,人们主要关注激素特异的转录因子的作用,但对于转录中介体的功能及作用机理     

嗜热四膜虫减数分裂研究进展

减数分裂是真核生物有性生殖过程的关键步骤,染色体的行为变化贯穿整个减数分裂的过程。近些年来,借助先进的分子生物学技术和细胞学实验手段,通过对突变细胞株的筛选和评价,单细胞真核模式生物原生动物嗜热四膜虫(Tetrahymena thermophila)减数分裂方面的研究取得了长足的进展。本文主要介绍嗜热四膜虫减数分裂的过程,以及在此过程中伴随染色体行为变化的相关基因的功能,从而为进一步探讨嗜热四膜虫减数分裂的分子机制提供有效信息。     

高等植物减数分裂的突变基因

精密有序的减数分裂是一个高度协调的生理、生化和遗传过程,受到许多基因的严格调节和控制。从而保证了物种的稳定性和连续性,保持了物种在生存斗争中不断进化的能力。一般称调节、控制减数分裂过程的基因为减数分裂基因。目前,对减数分裂基因的研究,已成为细胞遗传学的一个重要领域, 减数分裂基因结构或功能的任何改变,都可能引起减数分裂的变化。Gowen[19]等(1922)最先分离和描述了果蝇的不联会突变基因C(3)G。六十多年来,减数分裂突变基因的报道越来越多了。在大约130个高等植物种中,有关联会突变基因的报道就有100种类型。(Gottschalk[13]等,1980a、b;Koduru等1981;Kaul等1985)。研究表明,从前减数分裂的有丝分裂直到减数分裂后子细胞重新开始有丝分裂,整个过程的各种行为部可能受到突变基因的影响。     

A phylogenomic inventory of meiotic genes; evidence for sex in Giardia and an early eukaryotic origin of meiosis

Sexual reproduction in eukaryotes is accomplished by meiosis, a complex and specialized process of cell division that results in haploid cells (e.g., gametes). The stereotypical reductive division in meiosis is a major evolutionary innovation in eukaryotic cells, and delineating its history is key to understanding the evolution of sex. Meiosis arose early in eukaryotic evolution, but when and how meiosis arose and whether all eukaryotes have meiosis remain open questions. The known phylogenetic distribution of meiosis comprises plants, animals, fungi, and numerous protists. Diplomonads including Giardia intestinalis (syn. G. lamblia) are not known to have a sexual cycle; these protists may be an early-diverging lineage and could represent a premeiotic stage in eukaryotic evolution. We surveyed the ongoing G. intestinalis genome project data and have identified, verified, and analyzed a core set of putative meiotic genes-including five meiosis-specific genes-that are widely present among sexual eukaryotes. The presence of these genes indicates that: (1) Giardia is capable of meiosis and, thus, sexual reproduction, (2) the evolution of meiosis occurred early in eukaryotic evolution, and (3) the conserved meiotic machinery comprises a large set of genes that encode a variety of component proteins, including those involved in meiotic recombination.     

Variation and Evolution of Meiosis

Meiosis arose in the evolution of primitive unicellular organisms as a part of sexual process. One type of meiosis, the so-called classical type, predominates in all kingdoms of eukaryotes. Meiosis is controlled by hundreds of genes, both shared with mitosis and specifically meiotic ones. In a wide range of taxa, which in some cases include kingdoms, meiotic genes and features obey Vavilov's law of homologous variation series. Synaptonemal complexes (SCs) temporarily binding homologous chromosomes at prophase I, ensure precise and equal crossing over and interference. SC proteins have 60–80% homology within the class of mammals but differ from the corresponding proteins in fungi and insects. Thus, nonhomologous SC proteins perform similar functions in different taxa. Some recombination enzymes in fungi and plants have common epitopes. The molecular mechanism of recombination is inherited by eukaryotes from prokaryotes and operates in special compartments: SC recombination nodules. Chiasmata, i.e., physical crossovers of nonsister chromatids, are preserved in bivalents until metaphase I due to local cohesion of sister chromatids in the remaining SC fragments. Owing to chiasmata, homologous chromosomes participate in meiosis I in pairs rather than individually, which, along with unipolarity of kinetochores (only in meiosis 1), ensures segregation of homologous chromosomes. The appearance of SC and chiasmata played a key role in the evolution of unicellular organisms since it promoted the development of a progressive type of meiosis. Some lower eukaryotes retain primitive meiosis types. These primitive modes of meiosis also occur in the sex of some insects that is heterozygous for sex chromosomes. I suggest an explanation for these cases. Mutations at meiotic genes impair meiosis; however, due to the preservation of archaic meiotic genes in the genotype, bypass metabolic pathways arise, which provide partial rescue of the traits damaged by mutations. Individual blocks of genetic program of meiotic regulation have probably evolved independently.     

Variation and evolution of meiosis

Meiosis arose in the evolution of primitive unicellular organisms as a part of sexual process. One type of meiosis, the so-called classical type, predominates in all kingdoms of eukaryotes. Meiosis is controlled by hundreds of genes, both shared with mitosis and specifically meiotic ones. In a wide range of taxa, which in some cases include kingdoms, meiotic genes and features obey Vavilov's law of homologous variation series. Synaptonemal complexes (SCs) temporarily binding homologous chromosomes at prophase I, ensure precise and equal crossing over and interference. SC proteins have 60-80% homology within the class of mammals but differ from the corresponding proteins in fungi and plants. Thus, nonhomologous SC proteins perform similar functions in different taxa. Some recombination enzymes in fungi and insects have common epitopes. The molecular mechanism of recombination is inherited by eukaryotes from prokaryotes and operates in special compartments: SC recombination nodules. Chiasmata, i.e., physical crossovers of nonsister chromatids, are preserved in bivalents until metaphase I due to local cohesion of sister chromatids in the remaining SC fragments. Owing to chiasmata, homologous chromosomes participate in meiosis I in pairs rather than individually, which, along with unipolarity of kinetochores (only in meiosis 1), ensures segregation of homologous chromosomes. The appearance of SC and chiasmata played a key role in the evolution of unicellular organisms since it promoted the development of a progressive type of meiosis. Some lower eukaryotes retain primitive meiosis types. These primitive modes of meiosis also occur in the sex of some insects that is heterozygous for sex chromosomes. I suggest an explanation for these cases. Mutations at meiotic genes impair meiosis; however, due to the preservation of archaic meiotic genes in the genotype, bypass metabolic pathways arise, which provide partial rescue of the traits damaged by mutations. Individual blocks of genetic program of meiotic regulation have probably evolved independently.     

Using a meiosis detection toolkit to investigate ancient asexual "scandals" and the evolution of sex

Sexual reproduction is the dominant reproductive mode in eukaryotes but, in many taxa, it has never been observed. Molecular methods that detect evidence of sex are largely based on the genetic consequences of sexual reproduction. Here we describe a powerful new approach to directly search genomes for genes that function in meiosis. We describe a "meiosis detection toolkit", a set of meiotic genes that represent the best markers for the presence of meiosis. These genes are widely present in eukaryotes, function only in meiosis and can be isolated by degenerate PCR. The presence of most, or all, of these genes in a genome would suggest they have been maintained for meiosis and, implicitly, sexual reproduction. In contrast, their absence would be consistent with the loss of meiosis and asexuality. This approach will help to understand both meiotic gene evolution and the capacity for meiosis and sex in putative obligate asexuals.     

Time-course analysis of nuclear events during conjugation in the marine ciliate Euplotes vannus and comparison with other ciliates (Protozoa,Ciliophora)

Ciliates represent a morphologically and genetically distinct group of single-celled eukaryotes that segregate germline and somatic functions into two types of nuclei and exhibit complex cytogenetic events during the sexual process of conjugation, which is under the control of the so-called “mating type systems”. Studying conjugation in ciliates may provide insight into our understanding of the origins and evolution of sex and fertilization. In the present work, we studied in detail the sexual process of conjugation using the model species Euplotes vannus, and compared these nuclear events with those occurring in other ciliates. Our results indicate that in E. vannus: 1) conjugation requires about 75 hours to complete: the longest step is the development of the new macronucleus (ca. 64h), followed by the nuclear division of meiosis I (5h); the mitotic divisions usually take only 2h; 2) there are three prezygotic divisions (mitosis and meiosis I and II), and two of the eight resulting nuclei become pronuclei; 3) after the exchange and fusion of the pronuclei, two postzygotic divisions occur; two of the four products differentiate into the new micronucleus and macronucleus, respectively, and the parental macronucleus degenerates completely; 4) comparison of the nuclear events during conjugation in different ciliates reveals that there are generally three prezygotic divisions while the number of postzygotic divisions is highly variable. These results can serve as reference to investigate the mating type system operating in this species and to analyze genes involved in the different steps of the sexual process.     

An expanded inventory of conserved meiotic genes provides evidence for sex in Trichomonas vaginalis

Meiosis is a defining feature of eukaryotes but its phylogenetic distribution has not been broadly determined, especially among eukaryotic microorganisms (i.e. protists)-which represent the majority of eukaryotic 'supergroups'. We surveyed genomes of animals, fungi, plants and protists for meiotic genes, focusing on the evolutionarily divergent parasitic protist Trichomonas vaginalis. We identified homologs of 29 components of the meiotic recombination machinery, as well as the synaptonemal and meiotic sister chromatid cohesion complexes. T. vaginalis has orthologs of 27 of 29 meiotic genes, including eight of nine genes that encode meiosis-specific proteins in model organisms. Although meiosis has not been observed in T. vaginalis, our findings suggest it is either currently sexual or a recent asexual, consistent with observed, albeit unusual, sexual cycles in their distant parabasalid relatives, the hypermastigotes. T. vaginalis may use meiotic gene homologs to mediate homologous recombination and genetic exchange. Overall, this expanded inventory of meiotic genes forms a useful "meiosis detection toolkit". Our analyses indicate that these meiotic genes arose, or were already present, early in eukaryotic evolution; thus, the eukaryotic cenancestor contained most or all components of this set and was likely capable of performing meiotic recombination using near-universal meiotic machinery.     

Tetrahymena meiosis: Simple yet ingenious

The presence of meiosis, which is a conserved component of sexual reproduction, across organisms from all eukaryotic kingdoms, strongly argues that sex is a primordial feature of eukaryotes. However, extant meiotic structures and processes can vary considerably between organisms. The ciliated protist Tetrahymena thermophila, which diverged from animals, plants, and fungi early in evolution, provides one example of a rather unconventional meiosis. Tetrahymena has a simpler meiosis compared with most other organisms: It lacks both a synaptonemal complex (SC) and specialized meiotic machinery for chromosome cohesion and has a reduced capacity to regulate meiotic recombination. Despite this, it also features several unique mechanisms, including elongation of the nucleus to twice the cell length to promote homologous pairing and prevent recombination between sister chromatids. Comparison of the meiotic programs of Tetrahymena and higher multicellular organisms may reveal how extant meiosis evolved from proto-meiosis.     

Regulation of meiotic recombination and prophase I progression in mammals.

Meiosis is the process by which diploid germ cells divide to produce haploid gametes for sexual reproduction. The process is highly conserved in eukaryotes, however the recent availability of mouse models for meiotic recombination has revealed surprising regulatory differences between simple unicellular organisms and those with increasingly complex genomes. Moreover, in these higher eukaryotes, the intervention of physiological and sex-specific factors may also influence how meiotic recombination and progression are monitored and regulated. This review will focus on the recent studies involving mouse mutants for meiosis, and will highlight important differences between traditional model systems for meiosis (such as yeast) and those involving more complex cellular, physiological and genetic criteria.