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1.
We describe a process in meiotic cells of budding yeast in which chromosomes become joined together in pairs at their centromeres independent of chromosomal homology. These centromeric interactions depend on the synaptonemal complex component Zip1. During meiosis in wild-type diploids, centromere couples are initially nonhomologous and then undergo switching until all couples involve homologs. This transition to homologous coupling depends on Spo11, a protein required for the initiation of meiotic recombination. Regions of synaptonemal complex assembled early in meiosis are often centromere-associated. We propose that centromere coupling facilitates homolog pairing and promotes synapsis initiation. 相似文献
2.
The product of the mos proto-oncogene as a candidate "initiator" for oocyte maturation 总被引：49，自引：0，他引：49
N Sagata I Daar M Oskarsson S D Showalter G F Vande Woude 《Science (New York, N.Y.)》1989,245(4918):643-646
The endogenous c-mos product, pp39mos, is required for progesterone-induced meiotic maturation in Xenopus oocytes. Treatment of oocytes with progesterone induced a rapid increase in pp39mos that preceded both the activation of maturation promoting factor (MPF) and germinal vesicle breakdown (GVBD). Microinjection of synthetic mos RNA into oocytes activated MPF and induced GVBD in the absence of progesterone. Thus, the mos proto-oncogene product may qualify as a candidate "initiator" protein of MPF and is at least one of the "triggers" for G2 to M transition. 相似文献
3.
Fungi are nonmotile organisms that obtain carbon from compounds in their immediate surroundings. Confronted with nutrient limitation, the yeast Saccharomyces cerevisiae undergoes a dimorphic transition, switching from spherical cells to filaments of adherent, elongated cells that can invade the substratum. A complex web of sensing mechanisms and cooperation among signaling networks (including a mitogen-activated protein kinase cascade, cyclic adenosine monophosphate-dependent protein kinase, and 5'-adenosine monophosphate-activated protein kinase) elicits the appropriate changes in physiology, cell cycle progression, cell polarity, and gene expression to achieve this differentiation. Highly related signaling processes control filamentation and virulence of many human fungal pathogens. 相似文献
4.
ATR homolog Mec1 promotes fork progression,thus averting breaks in replication slow zones 总被引：1，自引：0，他引：1
Budding yeast Mec1, homolog of mammalian ATR, is an essential protein that mediates S-phase checkpoint responses and meiotic recombination. Elimination of Mec1 function leads to genomewide fork stalling followed by chromosome breakage. Breaks do not result from stochastic collapse of stalled forks or other incidental lesions; instead, they occur in specific regions of the genome during a G2 chromosomal transition. Break regions are found to be genetically encoded replication slow zones (RSZs), a newly discovered yeast chromosomal determinant. Thus, Mec1 has important functions in normal S phase and the genome instability of mec1 (and, analogously, ATR-/-) mutants stems from defects in these basic roles. 相似文献
5.
总结了影响减数分裂重组频率的诸多因素,探讨了提高减数分裂重组频率对植物远缘杂交中不良基因与优异基因的不利连锁打破的可能,并就当前的问题和今后的发展前景进行了讨论。 相似文献
6.
Zofall M Yamanaka S Reyes-Turcu FE Zhang K Rubin C Grewal SI 《Science (New York, N.Y.)》2012,335(6064):96-100
Facultative heterochromatin that changes during cellular differentiation coordinates regulated gene expression, but its assembly is poorly understood. Here, we describe facultative heterochromatin islands in fission yeast and show that their formation at meiotic genes requires factors that eliminate meiotic messenger RNAs (mRNAs) during vegetative growth. Blocking production of meiotic mRNA or loss of RNA elimination factors, including Mmi1 and Red1 proteins, abolishes heterochromatin islands. RNA elimination machinery is enriched at meiotic loci and interacts with Clr4/SUV39h, a methyltransferase involved in heterochromatin assembly. Heterochromatin islands disassemble in response to nutritional signals that induce sexual differentiation. This process involves the antisilencing factor Epe1, the loss of which causes dramatic increase in heterochromatic loci. Our analyses uncover unexpected regulatory roles for mRNA-processing factors that assemble dynamic heterochromatin to modulate gene expression. 相似文献
7.
Yuan L Liu JG Hoja MR Wilbertz J Nordqvist K Höög C 《Science (New York, N.Y.)》2002,296(5570):1115-1118
Aneuploidy (trisomy or monosomy) is the leading genetic cause of pregnancy loss in humans and results from errors in meiotic chromosome segregation. Here, we show that the absence of synaptonemal complex protein 3 (SCP3) promotes aneuploidy in murine oocytes by inducing defective meiotic chromosome segregation. The abnormal oocyte karyotype is inherited by embryos, which die in utero at an early stage of development. In addition, embryo death in SCP3-deficient females increases with advancing maternal age. We found that SCP3 is required for chiasmata formation and for the structural integrity of meiotic chromosomes, suggesting that altered chromosomal structure triggers nondisjunction. SCP3 is thus linked to inherited aneuploidy in female germ cells and provides a model system for studying age-dependent degeneration in oocytes. 相似文献
8.
We have identified a homolog of the mammalian p53 tumor suppressor protein in the nematode Caenorhabditis elegans that is expressed ubiquitously in embryos. The gene encoding this protein, cep-1, promotes DNA damage-induced apoptosis and is required for normal meiotic chromosome segregation in the germ line. Moreover, although somatic apoptosis is unaffected, cep-1 mutants show hypersensitivity to hypoxia-induced lethality and decreased longevity in response to starvation-induced stress. Overexpression of CEP-1 promotes widespread caspase-independent cell death, demonstrating the critical importance of regulating p53 function at appropriate levels. These findings show that C. elegans p53 mediates multiple stress responses in the soma, and mediates apoptosis and meiotic chromosome segregation in the germ line. 相似文献
9.
HRR25, a putative protein kinase from budding yeast: association with repair of damaged DNA 总被引：27，自引：0，他引：27
M F Hoekstra R M Liskay A C Ou A J DeMaggio D G Burbee F Heffron 《Science (New York, N.Y.)》1991,253(5023):1031-1034
In simple eukaryotes, protein kinases regulate mitotic and meiotic cell cycles, the response to polypeptide pheromones, and the initiation of nuclear DNA synthesis. The protein HRR25 from the budding yeast Saccharomyces cerevisiae was defined by the mutation hrr25-1. This mutation resulted in sensitivity to continuous expression of the HO double-strand endonuclease, to methyl methanesulfonate, and to x-irradiation. Homozygotes of hrr25-1 were unable to sporulate and disruption and deletion of HRR25 interfered with mitotic and meiotic cell division. Sequence analysis revealed two distinctive regions in the protein. The NH2-terminus of HRR25 contains the hallmark features of protein kinases, whereas the COOH-terminus is rich in proline and glutamine. Mutations in HRR25 at conserved residues found in all protein kinases inactivated the gene, and these mutants exhibited the hrr25 null phenotypes. Taken together, the hrr25 mutant phenotypes and the features of the gene product indicate that HRR25 is a distinctive member of the protein kinase superfamily. 相似文献
10.
Role of chloroplast protein kinase Stt7 in LHCII phosphorylation and state transition in Chlamydomonas 总被引：1，自引：0，他引：1
Photosynthetic organisms adapt to changes in light quality by redistributing light excitation energy between two photosystems through state transition. This reorganization of antenna systems leads to an enhanced photosynthetic yield. Using a genetic approach in Chlamydomonas reinhardtii to dissect the signal transduction pathway of state transition, we identified a chloroplast thylakoid-associated serine-threonine protein kinase, Stt7, that has homologs in land plants. Stt7 is required for the phosphorylation of the major light-harvesting protein (LHCII) and for state transition. 相似文献
11.
12.
Brar GA Yassour M Friedman N Regev A Ingolia NT Weissman JS 《Science (New York, N.Y.)》2012,335(6068):552-557
13.
对加拿大披碱草与老芒麦种间杂种F1的形态学和细胞学特征进行研究。形态学观察结果表明,杂种F1的穗形介于双亲之间,呈半弯曲形,其母本加拿大披碱草植株浅绿色,茎粗糙,穗粗大而弯曲,每节2～3小穗,颖和外稃粗糙具短毛。父本老芒麦全株粉绿色,穗状花序疏松下垂,每节2小穗,每小穗3～5小花。杂种F1植株灰绿色,粗糙,外稃和颖具柔毛,偏向母本加拿大披碱草。加拿大披碱草染色体都是由中部着丝粒染色体组成,染色体相对长度范嗣在10～4．65,最长染色体与最短染色体之比为2．2：1,臂比介于1．14～1．35。染色体核型公式为2n=4x=28m,属于1A类型。老芒麦染色体核型公式为2n=4x=22m＋6sin,属于1B型;F1的染色体数为2n=4x=28,染色体相对长度的变异范围在8．83～4．42,臂比疽变化在1．00～3．33。其中,第1、5、7、9、11、12、13、14对染色体为正中着丝粒（M）染色体,第3对为近端着丝粒染色体,剩下的染色体为中部着丝粒染色体,其中,正中着丝粒（M）染色体的数目增加,近中着丝粒染色体（sm）已不存在。L／S恰好为2：1,核型类型为2B。核型公式为2i=4x=16M＋lOre＋2st。通过形态学和染色体的核型分析可以初步确定,F1是真杂种;但杂种F1不结实。加拿大披碱草和老芒麦含有落后染色体细胞的频率较低,分别为0．96％和2．76％;F1减数分裂后期染色体的分配出现了异常行为,染色体有落后现象,落后的染色体细胞频率较高,达87．37％,F1在减数分裂中期一部分染色体也能配对形成二价体,但染色体配对杂乱无章,棒状二价体占多数,环状二价体较少,且出现多价体。 相似文献
14.
细胞松弛素B对牛卵母细胞体外成熟过程中微管、微丝及染色体的影响 总被引：1，自引：0，他引：1
细胞松弛素B(Cytochalasin B,CB)是一种抑制微丝聚合的药物,能抑制微丝的组装从而阻止胞质分裂和极体排放,是研究细胞分裂器形成与变化的重要药物。在牛卵母细胞体外成熟培养过程中加入7.5 μg/mL的CB进行处理,分析CB对减数分裂过程中细胞骨架形态、染色体的排列与分离等方面的影响。结果显示,CB处理后卵母细胞第一极体的排放受到了抑制,染色体的排列和分离受到了影响,出现了同源染色体分离不完全或分离不均匀及分离后又聚在一起等异常情况,形成许多二倍体卵母细胞;纺锤体微管的形态发生了变化,出现了两个纺锤体、巨大纺锤体和多极纺锤体等异常结构;微丝的正常分布受到了影响,染色体周围没有或少有微丝分布,皮质下的微丝分布也变得少而不均匀;这说明微丝与微管在减数分裂过程中是协同作用的,CB通过影响微丝的动态变化,改变了纺锤体微管的形态结构,最终抑制了极体的排放。 相似文献
15.
【目的】通过SCP3蛋白免疫荧光染色法,研究小鼠初级精母细胞减数分裂前期Ⅰ不同分裂相联会复合体的形态变化。【方法】从小鼠睾丸取曲细精管,用铺展法制片,对初级精母细胞SCP3蛋白进行免疫荧光染色,观察减数分裂前期Ⅰ不同分裂相联会复合体的形态变化。【结果】在细线期,可见短小、不连续而杂乱簇聚的SCP3蛋白片段;在偶线期,SCP3蛋白趋于明显,连续并呈线状,但没有形成完整的联会复合体;在粗线期,SCP3蛋白结构完整而清晰,小鼠初级精母细胞联会复合体共有20条,包括19条常染色体联会复合体和1条XY联会复合体;双线期,构成联会复合体的2条SCP3蛋白开始相互排斥而分离,导致联会复合体开始解体,但此时的二价体结构依然清晰可见。【结论】SCP3蛋白免疫荧光染色是研究减数分裂前期Ⅰ不同分裂相联会复合体形态变化的强有力工具。 相似文献
16.
Direct observation of global protein motion in hemoglobin and myoglobin on picosecond time scales 总被引：3，自引：0，他引：3
Picosecond phase-grating spectroscopy is highly sensitive to density changes and provides a new holographic approach to the study of protein dynamics. Photodissociation of carbon monoxide from heme proteins induces a well-defined transition from a ligated to a deoxy structure that is important to hemoglobin and myoglobin functionality. Grating spectroscopy was used to observe protein-driven density waves on a picosecond time scale after carbon monoxide dissociation. This result demonstrates that global tertiary structure changes of proteins occur on an extremely fast time scale and provides new insight into the biomechanics of deterministic protein motion. 相似文献
17.
Meiotic recombination in budding yeast requires two RecA-related proteins, Rad51 and Dmc1, both of which form filaments on DNA capable of directing homology search and catalyzing formation of homologous joint molecules (JMs) and strand exchange. With use of a separation-of-function mutant form of Rad51 that retains filament-forming but not JM-forming activity, we show that the JM activity of Rad51 is fully dispensable for meiotic recombination. The corresponding mutation in Dmc1 causes a profound recombination defect, demonstrating Dmc1's JM activity alone is responsible for meiotic recombination. We further provide biochemical evidence that Rad51 acts with Mei5-Sae3 as a Dmc1 accessory factor. Thus, Rad51 is a multifunctional protein that catalyzes recombination directly in mitosis and indirectly, via Dmc1, during meiosis. 相似文献
18.
为研究同源多倍化对拟南芥减数分裂前期Ⅰ过程的影响,以哥伦比亚生态型(Columbia)二倍体拟南芥为试验材料,经0.2%秋水仙素加倍处理,利用流式细胞仪和细胞学方法鉴定倍性,获得同源多倍体拟南芥;分析同源多倍体拟南芥的形态特征,利用荧光显微观察不同倍性拟南芥的减数分裂前期Ⅰ过程,并利用荧光定量PCR技术分析与减数分裂前期Ⅰ过程相关的基因的表达变化。结果表明,与二倍体拟南芥相比,在细胞学水平上,不同倍性拟南芥的减数分裂过程基本一致;在分子水平上,多倍化对拟南芥减数分裂产生一定影响,同源重组相关基因的表达量呈现上调或下调的变化,且功能相关或有相互作用关系的基因的表达量变化趋势相似。 相似文献
19.
Crackower MA Kolas NK Noguchi J Sarao R Kikuchi K Kaneko H Kobayashi E Kawai Y Kozieradzki I Landers R Mo R Hui CC Nieves E Cohen PE Osborne LR Wada T Kunieda T Moens PB Penninger JM 《Science (New York, N.Y.)》2003,300(5623):1291-1295
Meiosis is a critical stage of gametogenesis in which alignment and synapsis of chromosomal pairs occur, allowing for the recombination of maternal and paternal genomes. Here we show that FK506 binding protein (Fkbp6) localizes to meiotic chromosome cores and regions of homologous chromosome synapsis. Targeted inactivation of Fkbp6 in mice results in aspermic males and the absence of normal pachytene spermatocytes. Moreover, we identified the deletion of Fkbp6 exon 8 as the causative mutation in spontaneously male sterile as/as mutant rats. Loss of Fkbp6 results in abnormal pairing and misalignments between homologous chromosomes, nonhomologous partner switches, and autosynapsis of X chromosome cores in meiotic spermatocytes. Fertility and meiosis are normal in Fkbp6 mutant females. Thus, Fkbp6 is a component of the synaptonemal complex essential for sex-specific fertility and for the fidelity of homologous chromosome pairing in meiosis. 相似文献
20.
Fleury PA 《Science (New York, N.Y.)》1981,211(4478):125-131
Transformations among many of the diverse states of matter arise from microscopic interactions involving very many (approximately 10(23)) constituent particles and result in dramatic changes in macroscopic properties. The values of some physical parameters vanish, while others approach infinity. These changes and their evolution are strikingly similar in systems as apparently different as liquids, magnets, superconductors, ferroelectrics, and liquid crystals, which suggests that there is an underlying unity to phase transition phenomena. The basis and extent of this unity are reviewed for many-body systems in equilibrium, and analogies with instability phenomena in systems far from equilibrium (such as lasers, fluid flows, and avalanche electronic devices) are pointed out. 相似文献