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1.
Mammalian X inactivation turns off one female X chromosome to enact dosage compensation between XX and XY individuals. X inactivation is known to be regulated in cis by Xite, Tsix, and Xist, but in principle the two Xs must also be regulated in trans to ensure mutually exclusive silencing. Here, we demonstrate that interchromosomal pairing mediates this communication. Pairing occurs transiently at the onset of X inactivation and is specific to the X-inactivation center. Deleting Xite and Tsix perturbs pairing and counting/choice, whereas their autosomal insertion induces de novo X-autosome pairing. Ectopic X-autosome interactions inhibit endogenous X-X pairing and block the initiation of X-chromosome inactivation. Thus, Tsix and Xite function both in cis and in trans. We propose that Tsix and Xite regulate counting and mutually exclusive choice through X-X pairing. 相似文献
2.
Sensing X chromosome pairs before X inactivation via a novel X-pairing region of the Xic 总被引：1，自引：0，他引：1
Augui S Filion GJ Huart S Nora E Guggiari M Maresca M Stewart AF Heard E 《Science (New York, N.Y.)》2007,318(5856):1632-1636
3.
Intersection of the RNA interference and X-inactivation pathways 总被引：1，自引：0，他引：1
In mammals, dosage compensation is achieved by X-chromosome inactivation (XCI) in the female. The noncoding Xist gene initiates silencing of the X chromosome, whereas its antisense partner Tsix blocks silencing. The complementarity of Xist and Tsix RNAs has long suggested a role for RNA interference (RNAi). Here, we report that murine Xist and Tsix form duplexes in vivo. During XCI, the duplexes are processed to small RNAs (sRNAs), most likely on the active X (Xa) in a Dicer-dependent manner. Deleting Dicer compromises sRNA production and derepresses Xist. Furthermore, without Dicer, Xist RNA cannot accumulate and histone 3 lysine 27 trimethylation is blocked on the inactive X (Xi). The defects are partially rescued by truncating Tsix. Thus, XCI and RNAi intersect, down-regulating Xist on Xa and spreading silencing on Xi. 相似文献
4.
非编码KNAXist介导的X染色体失活是表观遗传研究的一个典范,该系统能使一整条染色体变为异染状态。从Xist与X染色体计数、失活的选择、失活的起始和失活的维持等方面综述了其分子机制。 相似文献
5.
To equalize X-chromosome dosages between the sexes, the female mammal inactivates one of her two X chromosomes. X-chromosome inactivation (XCI) is initiated by expression of Xist, a 17-kb noncoding RNA (ncRNA) that accumulates on the X in cis. Because interacting factors have not been isolated, the mechanism by which Xist induces silencing remains unknown. We discovered a 1.6-kilobase ncRNA (RepA) within Xist and identified the Polycomb complex, PRC2, as its direct target. PRC2 is initially recruited to the X by RepA RNA, with Ezh2 serving as the RNA binding subunit. The antisense Tsix RNA inhibits this interaction. RepA depletion abolishes full-length Xist induction and trimethylation on lysine 27 of histone H3 of the X. Likewise, PRC2 deficiency compromises Xist up-regulation. Therefore, RepA, together with PRC2, is required for the initiation and spread of XCI. We conclude that a ncRNA cofactor recruits Polycomb complexes to their target locus. 相似文献
6.
The initiation of X-chromosome inactivation is thought to be tightly correlated with early differentiation events during mouse development. Here, we show that although initially active, the paternal X chromosome undergoes imprinted inactivation from the cleavage stages, well before cellular differentiation. A reversal of the inactive state, with a loss of epigenetic marks such as histone modifications and polycomb proteins, subsequently occurs in cells of the inner cell mass (ICM), which give rise to the embryo-proper in which random X inactivation is known to occur. This reveals the remarkable plasticity of the X-inactivation process during preimplantation development and underlines the importance of the ICM in global reprogramming of epigenetic marks in the early embryo. 相似文献
7.
R L Teplitz 《Science (New York, N.Y.)》1965,150(705):1828-1829
Each retinal cone cell of the female contains a sex-chromatin body not present in coinparable material from the male. Therefore the lack of detectable "patch" formation in female heterozygotes for red color-blindness (as expected from the X-inactivation hypothesis) cannot be attributed to failure of Barr-body formation. 相似文献
8.
9.
Gordon P 《Science (New York, N.Y.)》2004,306(5695):496-499
Members of the Pirah? tribe use a "one-two-many" system of counting. I ask whether speakers of this innumerate language can appreciate larger numerosities without the benefit of words to encode them. This addresses the classic Whorfian question about whether language can determine thought. Results of numerical tasks with varying cognitive demands show that numerical cognition is clearly affected by the lack of a counting system in the language. Performance with quantities greater than three was remarkably poor, but showed a constant coefficient of variation, which is suggestive of an analog estimation process. 相似文献
10.
BAILEY DW 《Science (New York, N.Y.)》1963,141(3581):631-633
The histoincompatibility determined by one or more genes on the X chromosome of the mouse effects a complete rejection of skin of the (C57BL/6 female symbol x BALB/c male symbol) F(1) hybrid male grafted onto the reciprocal type F(1) hybrid male, but only an incomplete rejection of either reciprocal type F(1) hybrid female skin, grafted onto the same type of male host. The resulting mosaic survival pattern of the female graft is interpreted as support for the Lyon hypothesis of X-chromosome inactivation. 相似文献
11.
MASSINI P 《Science (New York, N.Y.)》1961,133(3456):877-878
The shape of the self-absorption correction curve of beta-emitters is not universal but depends on the geometrical arrangement of the sample and counting device. This may explain why the correction factor defined by Hendler (1) is not always linearly related to the thickness of the sample. 相似文献
12.
Parisi M Nuttall R Naiman D Bouffard G Malley J Andrews J Eastman S Oliver B 《Science (New York, N.Y.)》2003,299(5607):697-700
Sex chromosomes are primary determinants of sexual dimorphism in many organisms. These chromosomes are thought to arise via the divergence of an ancestral autosome pair and are almost certainly influenced by differing selection in males and females. Exploring how sex chromosomes differ from autosomes is highly amenable to genomic analysis. We examined global gene expression in Drosophila melanogaster and report a dramatic underrepresentation of X-chromosome genes showing high relative expression in males. Using comparative genomics, we find that these same X-chromosome genes are exceptionally poorly conserved in the mosquito Anopheles gambiae. These data indicate that the X chromosome is a disfavored location for genes selectively expressed in males. 相似文献
13.
Tenaillon O Rodríguez-Verdugo A Gaut RL McDonald P Bennett AF Long AD Gaut BS 《Science (New York, N.Y.)》2012,335(6067):457-461
To estimate the number and diversity of beneficial mutations, we experimentally evolved 115 populations of Escherichia coli to 42.2°C for 2000 generations and sequenced one genome from each population. We identified 1331 total mutations, affecting more than 600 different sites. Few mutations were shared among replicates, but a strong pattern of convergence emerged at the level of genes, operons, and functional complexes. Our experiment uncovered a set of primary functional targets of high temperature, but we estimate that many other beneficial mutations could contribute to similar adaptive outcomes. We inferred the pervasive presence of epistasis among beneficial mutations, which shaped adaptive trajectories into at least two distinct pathways involving mutations either in the RNA polymerase complex or the termination factor rho. 相似文献
14.
Osterloh JM Yang J Rooney TM Fox AN Adalbert R Powell EH Sheehan AE Avery MA Hackett R Logan MA MacDonald JM Ziegenfuss JS Milde S Hou YJ Nathan C Ding A Brown RH Conforti L Coleman M Tessier-Lavigne M Züchner S Freeman MR 《Science (New York, N.Y.)》2012,337(6093):481-484
Axonal and synaptic degeneration is a hallmark of peripheral neuropathy, brain injury, and neurodegenerative disease. Axonal degeneration has been proposed to be mediated by an active autodestruction program, akin to apoptotic cell death; however, loss-of-function mutations capable of potently blocking axon self-destruction have not been described. Here, we show that loss of the Drosophila Toll receptor adaptor dSarm (sterile α/Armadillo/Toll-Interleukin receptor homology domain protein) cell-autonomously suppresses Wallerian degeneration for weeks after axotomy. Severed mouse Sarm1 null axons exhibit remarkable long-term survival both in vivo and in vitro, indicating that Sarm1 prodegenerative signaling is conserved in mammals. Our results provide direct evidence that axons actively promote their own destruction after injury and identify dSarm/Sarm1 as a member of an ancient axon death signaling pathway. 相似文献
15.
本文讨论了金尖茶渥堆色变的主导因素。发现物理、化学的“湿热”作用是主要因素,而酶促氧化和霉菌只起辅助作用。本文还讨论了金尖茶渥堆工序的影响因素,确认以叶温、叶含水量、氧气为渥堆形成金尖茶品质特征的主要因素。从而构成最佳品质的正交试验权数选择为“2·1·2·2”。 相似文献
16.
Output from the circadian clock controls rhythmic behavior through poorly understood mechanisms. In Drosophila, null mutations of the neurofibromatosis-1 (Nf1) gene produce abnormalities of circadian rhythms in locomotor activity. Mutant flies show normal oscillations of the clock genes period (per) and timeless (tim) and of their corresponding proteins, but altered oscillations and levels of a clock-controlled reporter. Mitogen-activated protein kinase (MAPK) activity is increased in Nf1 mutants, and the circadian phenotype is rescued by loss-of-function mutations in the Ras/MAPK pathway. Thus, Nf1 signals through Ras/MAPK in Drosophila. Immunohistochemical staining revealed a circadian oscillation of phospho-MAPK in the vicinity of nerve terminals containing pigment-dispersing factor (PDF), a secreted output from clock cells, suggesting a coupling of PDF to Ras/MAPK signaling. 相似文献
17.
自花结实鸭梨授粉受精过程中生理代谢变化规律研究 总被引：1，自引：0，他引：1
对鸭梨及其自花结实变异品种--"金坠梨"和"魏县阎庄自花结实鸭梨"的自花授粉表现、花柱抗氧化酶活性、MDA含量、内源激素含量及比值进行了研究.结果表明:"金坠梨"和"魏县阎庄自花结实鸭梨"自花授粉后,花粉管能进入花柱,在沿花柱向子房伸长途中未被抑制,花粉管能顺利通过花柱进入胚囊,并能完成受精作用.鸭梨的自花结实变异品种... 相似文献
18.
Site-specific X-chromosome rearrangements from hybrid dysgenesis in Drosophila melanogaster 总被引：10，自引：0，他引：10
When the germ line of Drosophila males is destabilized by a syndrome known as hybrid dysgenesis, X-chromosome rearrangements are found in up to 10 percent of the gametes produced. Some of these aberrations are simple inversions, but many are complex multibreak rearrangements. Furthermore, most of the breakpoints fall into a few highly localized positions on the chromosome. These positions are mostly at points of intercalary heterochromatin and may vary from one strain to the next. the results suggest that they may represent points of insertion of mobile DNA sequences. 相似文献
19.
东北细毛羊和蒙古羊染色体组型特征及其与山羊染色体组型进化的关系 总被引：5，自引：0，他引：5
本文采用外周血淋巴细胞培养法研究了蒙古羊和东北细毛羊的染色体组型和分带。结果表明,其二倍体数目均为2n=54.54条染色体共分出124条带。两种绵羊染色体中A组3对中着丝点染色体和x染色体没有明显的C带区,y染色体染得略深且均匀,B组23对常染色体C带深染且呈多态性。另外,本文还对这两种绵羊与成都麻羊从染色体组型和分带等方面进行了比较,为山羊、绵羊由2n=60共同祖先进化而来这一假说提供了又一证据。 相似文献
20.
M A Goldman K R Stokes R L Idzerda G S McKnight R E Hammer R L Brinster S M Gartler 《Science (New York, N.Y.)》1987,236(4801):593-595
Mammalian X-chromosome inactivation involves a coordinate shutting down of physically linked genes. Several proposed models require the presence of specific sequences near genes to permit the spread of inactivation into these regions. If such models are correct, one might predict that heterologous genes transferred onto the X chromosome might lack the appropriate signal sequences and therefore escape inactivation. To determine whether a foreign gene inserted into the X chromosome is subject to inactivation, transgenic mice harboring 11 copies of the complete, 17-kilobase chicken transferrin gene on the X chromosome were used. Male mice hemizygous for this insert were bred with females bearing Searle's translocation, an X-chromosome rearrangement that is always active in heterozygous females (the unrearranged X chromosome is inactive). Female offspring bearing the Searle's translocation and the chicken transferrin gene had the same amount of chicken transferrin messenger RNA in liver as did transgenic male mice or transgenic female mice lacking the Searle's chromosome. This result shows that the inserted gene is not subject to X-chromosome inactivation and suggests that the inactivation process cannot spread over 187 kilobases of DNA in the absence of specific signal sequences required for inactivation. 相似文献