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X inactivation definition - Medical Dictionary definitions of popular medical terms X inactivation: The phenomenon in a female by which one X chromosome (either the maternally or paternally derived X) is randomly (by chance) inactivated in an early embryonic cell, with fixed inactivation of that same X in all cells descended from that cell. The change that occurs with X inactivation is epigenetic: it is a heritable change in gene function without a change in the sequence of the DNA. The phenomenon of X inactivation is also called lyonization after the English geneticist Mary Lyon (1925-) who first described it. www.medterms.com /script/main/art.asp?articlekey=26391   (249 words)

PIBS Faculty Barbara Panning X chromosome inactivation is mediated by Xist RNA stabilization. X chromosome inactivation is initiated during post-implantation development, when cells differentiate from pluripotent to more restricted cell types. X inactivation: Tsix and Xist as yin and yang. www.ucsf.edu /pibs/faculty/panning.html   (496 words)

CAMB: Faculty: Marisa S. Bartolomei X inactivation is the dosage compensation mechanism that female mammals use to silence one X chromosome and to achieve equivalent X-linked expression to males. While all factors known to be involved in X inactivation map to the X chromosome, it is probable that unidentified autosomal factors are essential to the process. The observation that 6.5 day embryos are affected by the mutations suggests that we have disrupted autosomal factors that act early in the X inactivation pathway. www.med.upenn.edu /camb/faculty/db/bartolomei.html   (853 words)

X chromosome - Define Your World of X chromosome by the Free Online Dictionary, Thesaurus and Encyclopedia. X chromosome is one of the two sex chromosomes in mammals (the other is the Y chromosome). Males have one X chromosome and one Y chromosome. The DNA sequence of the human X chromosome The human X chromosome has a unique biology that was shaped by its evolution as the sex chromosome shared by males and females. www.valuesponsor.com /encyclopedia/X+chromosome   (333 words)

mammalian X chromosome inactivation X inactivation is an example of large scale, developmentally directed, co-ordinate regulation of gene expression and thus is a good model in which to study the mechanisms controlling cell fate. In mammals, the dosage of X linked genes in males and females is equalised by the inactivation, early in embryogenesis, of genes on one of the two X chromosomes in the cells of females. The molecular mechanism of mammalian X chromosome inactivation www.science.uts.edu.au /centres/mgu/mammalian.html   (900 words)

X Inactivation. X inactivation is a chromosome-specific form of genetic regulation in which thousands of genes on one homologue become silenced early in female embryogenesis. Tsix and Xist seem to have a yin and yang relationship, with opposite effects on X inactivation. In all the cells of the extraembryonic membranes, it is father's X chromosome that is inactivated. members.shaw.ca /copingwithillness/xinact.html   (8036 words)

Fragile X - Fragile X Syndrome - Mental Retardation - Genetic Defects - Autism - Learning Disabilities - Medical Research In Israel In females with normal random X inactivation, the maternally inherited gene is active in ~50% of her cells, with the paternally inherited gene being active in the rest. Males have 1 X chromosome, which is maternally inherited, and a Y chromosome, which is passed down from father to son. The X chromosomes are usually inactivated randomly so that the maternal and paternal X chromosomes would each be used in about half of a woman’s cells. www.cfxf.org /news_1.php   (875 words)

Pregnancy Outcome in Recurrent Miscarriage Patients With Skewed X Chromosome Inactivation -- Sullivan et al. 101 (6): 1236 -- Obstetrics & Gynecology is methylated on the inactive X chromosome and unmethylated with idiopathic recurrent miscarriage for skewed X chromosome the androgen receptor gene from the undigested (inactive) X www.greenjournal.org /cgi/content/full/101/6/1236   (3166 words)

X inactivation The researchers found that distribution of escapees on the "arms" of an inactivated X chromosome is not random, with 30 percent of the genes on the short arm escaping inactivation, compared to only 3 percent of the genes on the long arm. In mammals, most of the several thousand genes located on one of a female's two X chromosomes are silenced through a mechanism known as X inactivation, which likely evolved to equalize the impact of X-linked genes in males and females. Both the large number of genes that escape inactivation and their non-random distribution have implications for counseling individuals who have structurally abnormal X chromosomes. www.cwru.edu /pubs/cnews/1999/12-9/x-gene.htm   (333 words)

X Inactive-Specific Transcript (Xist) Expression and X Chromosome Inactivation in the Preattachment Bovine Embryo -- De La Fuente et al. 60 (3): 769 -- Biology of Reproduction and the onset of X chromosome inactivation in bovine preattachment X inactivation has been considered to be essential for germ X Inactive-Specific Transcript (Xist) Expression and X Chromosome Inactivation in the Preattachment Bovine Embryo www.biolreprod.org /cgi/content/full/60/3/769   (5419 words)

Variation in Women's X Chromosomes May Explain Differences Among Individuals, Between Sexes The incomplete nature of X inactivation, demonstrated in the new study, means that at least 15 percent of the X-linked genes, and their protein products, are present at characteristically higher, and often variable, levels in females compared to males. However, the large number of genes that escape inactivation and their concentration in certain portions of the X chromosome has immediate implications for counseling the one in every 650 individuals born with X chromosome abnormalities, Willard said. Originally, scientists had assumed that the inactivation process resulted in complete silencing of the genes on the second X chromosome, Willard said, in order to leave both sexes with the same activity level, or dosage, of the genes encoded by the X chromosome. www.medicalnewstoday.com /medicalnews.php?newsid=21395   (970 words)

Chromosomal basis of X chromosome inactivation: Identification of a multigene domain in Xp11.21-p11.22 that escapes X inactivation -- Miller and Willard 95 (15): 8709 -- Proceedings of the National Academy of Sciences Six genes that escape inactivation map exclusively within a domain (denoted by the shaded oval) that is transcriptionally active on the inactive X chromosome. X chromosome inactivation is the process whereby one of the two X chromosomes in normal diploid female cells is inactivated X inactivation in humans is that certain genes have been found www.pnas.org /cgi/content/full/95/15/8709   (5238 words)

Whitehead Institute - X-inactivation Since Dolly was first cloned, researchers have debated whether she has random X-inactivation as normal females do or the same X chromosome inactivated in all her cells (the X that was inactive in the mammary cell nucleus from which she had been cloned). When researchers analyzed the results they found that X-inactivation is random in the embryonic lineage of cloned mice. The X-inactivation is random in the embryonic tissue, but in the tissue that ultimately becomes the placenta, the inactivation is thought to happen by a process called imprinting in which the paternal X is marked for inactivation. www.wi.mit.edu /news/archives/2000/dp_1123.html   (980 words)

Control of Xist expression for imprinted and random X chromosome inactivation in mice -- Matsui et al. 10 (13): 1393 -- Human Molecular Genetics 21 Takagi, N. and Sasaki, M. (1975) Preferential inactivation of the paternally derived X chromosome in the extraembryonic membranes of the mouse. X chromosome, but detailed mechanisms remain to be defined (25–27). 37 Goto, Y. and Takagi, N. (2000) Maternally inherited X chromosome is not inactivated in mouse blastocysts due to parental imprinting. hmg.oxfordjournals.org /cgi/content/full/10/13/1393   (4888 words)

FOCUS March 24, 2006 GENETICS: X Inactivation Seen As Contact Sport The X inactivation center on both chromosomes is in the open state before X inactivation, and the future active X remains that way. This timing coincided with X inactivation, and the X inactivation center was the portion of the chromosome where the contact occurred. When the X inactivation center was removed from chromosomes, they failed to pair up. focus.hms.harvard.edu /2006/032406/genetics.shtml   (1058 words)

Transient colocalization of X-inactivation centres accompanies the initiation of X inactivation - Nature Cell Biology The initial differential treatment of the two X chromosomes during X-chromosome inactivation is controlled by the X-inactivation centre (Xic). However, little is known about the process that ensures that X inactivation is triggered appropriately when more than one Xic is present in a cell. This locus determines how many X chromosomes are present in a cell ('counting') and which X chromosome will be inactivated in female cells ('choice'). www.nature.com /ncb/journal/v8/n3/abs/ncb1365.html   (361 words)

DEVELOPMENTAL BIOLOGY: ON INACTIVATION OF THE X CHROMOSOME Later on, in the embryonic tissues, X inactivation is random with respect to the parental origin of the X chromosomes[4]. This meiotic inactivation uniquely affects the sex chromosomes and may be associated with the inability of the X and Y chromosomes to pair during male meiosis[5]. DEVELOPMENTAL BIOLOGY: ON INACTIVATION OF THE X CHROMOSOME scienceweek.com /2005/sw051230-4.htm   (2233 words)

Science Notes -- Summer 1998 The homologs on the Y--and this has been proven in the case of one gene--appear functionally interchangeable with their cousins on the X. Genes that escape X inactivation and have Y homologs are caught in intermediate stages of evolution. on the inactivated X chromosome of a human female are known to escape inactivation. But no cases are known in which a gene is subject to X inactivation yet has a Y homolog that remains conserved in structure and widely expressed. scicom.ucsc.edu /scinotes/9801/chromes/3.html   (711 words)

Jeannie T. Lee She is also interested in the mechanistic and evolutionary relationship between X inactivation and imprinting. Her recent work suggests that imprinted X-chromosome inactivation is directly connected to meiotic sex chromosome inactivation in the male germline. In contrast, during imprinted XCI, the father's X chromosome is inactivated in all cells. www.hhmi.org /research/investigators/lee.html   (1860 words)

Goldman CV A chicken transferrin gene on the X chromosome of transgenic mice escapes X-chromosome inactivation. X-chromosome inactivation and DNA methylation in transgenic mice. Senior fellow in medical genetics, University of Washington, Seattle, studying chromatin structure and its relationship to X-chromosome inactivation, and X-chromosome inactivation in transgenic mice. online.sfsu.edu /~mgoldman/cv.html   (4438 words)

Protocols Used at NCI.,DNA, Clonality-X Chromosome Inactivation Assay Investigators can utilize X chromosome inactivation (methylation) to determine the clonality status of a tumor or premalignant lesion in females. Protocols Used at NCI.,DNA, Clonality-X Chromosome Inactivation Assay Methylation of HpaII and HhaI sites near the polymorphic CAG repeat in the human androgen-receptor gene correlates with X chromosome inactivation. cgap-mf.nih.gov /Protocols/DNARNAProteomicAnalysis/DNA/DNAProtocols/Clonality.html   (751 words)

Current Research Focusing on Euchromatin Within the Cell Nucleus. Wutz A, and Jaenisch R, "A Shift from Reversible to Irreversible X Inactivation is Triggered during ES Cell Differentiation". Yu X, Zhu X, Pi W, Ling J, Ko L, Takeda Y, and Tuan D, "The LTR of ERV-9 human endogenous retrovirus binds to NF-Y in the assembly of an active LTR enhancer complex NF-Y/MZF1/GATA-2". Liao X, Li Y, Bonini C, Nair S, Gilboa E, Greenberg PD, and Yee C, "Transfection of RNA Encoding Tumor Antigens Following Maturation of Dendritic Cells Leads to Prolonged Presentation of Antigen and the Generation of High-Affinity Tumor-Reactive Cytotoxic T Lymphocytes". www.euchromatin.net /current1.html   (10498 words)

Publications Lyon, M.F. (2001): The discovery of X-Chromosome inactivation Liu, X. Oliver, F. Brown, S.D.M. Denny, P. Keightley, P.D. (2001): High-resolution quantitative trait locus mapping for body weight in mice by recombinant progeny testing www.mgu.har.mrc.ac.uk /publications/index.html?date=2001   (778 words)

Medical Dictionary definitions of popular medical terms A B C D E F G H I J K L M N O P Q R S T U V W X Y Z MedicineNet Home > MedTerms medical dictionary A-Z List > X Please consult your healthcare provider before beginning any course of supplementation or treatment. www.medterms.com /script/main/alphaidx.asp?p=x_dict   (175 words)

RexAB proteins of bacteriophage lambda enhance the effect of photolyase-dimer complexes on lacZ gene expression in Escherichia coli. Inactivation is exceptionally effective when cells contain amplified levels of DNA photolyase (which forms complexes with pyrimidine dimers in the absence of light for actual photoreversal) and a lambda prophage. UV-inactivation of lacZ gene expression in the presence of both amplified photolyase and lambda is even more effective if lambda cI857 is used in place of the wildtype prophage but is wholly unexceptional if the prophage carries defects in the lambda genes rexA or rexB. When Rex AB proteins are provided by expression from a plasmid and the cell also contains amplified photolyase, exceptional inactivation rates again obtain; in fact inactivation is most effective under these conditions. www.aegis.com /aidsline/1992/jun/M9260195.html   (481 words)

Okadaic acid-sensitive activation of Maxi Cl- channels by triphenylethylene antioestrogens in C1300 mouse neuroblastoma cells -- Diaz et al. 536 (1): 79 -- The Journal of Physiology Online The current was characterised by inactivation at negative potentials and, unlike the Maxi Cl currents that have been activated by antioestrogens in fibroblasts (Hardy and Valverde, 1994), presented little inactivation at positive potentials. Valverde: Unitat de Senyalització Cellular, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, C/ Dr. Aiguader 80, 08003 Barcelona, Spain. While the channel in the fibroblasts shows marked inactivation at positive and negative potentials (Hardy and Valverde, 1994), the channel in the neuroblastoma cell line (this study) only presented inactivation at negative potentials, although the inactivation constant varied greatly from cell to cell. jp.physoc.org /cgi/content/full/536/1/79   (5586 words)

Proc. of Students' Research Vol.9 Photoreactivation of Escherichia coli subsequent to inactivation by a low-pressure or a medium-pressure UV lamp A medium-pressure UV lamp (MP; 220nm-580nm) was compared with a conventional low-pressure UV lamp (LP; 254nm) from the viewpoint of inactivation and the subsequent photoreactivation of Escherichia coli. In case the inactivation level was 99.9%, LP inactivation led to photoreactivation while almost no photoreactivation was observed subsequent to MP inactivation. www.env.t.u-tokyo.ac.jp /e/research/st_proc/Proc02/ohgakilab.html   (1586 words)

Selective potentiation of N-type calcium channels by angiotensin II in rat subfornical organ neurones -- Washburn and Ferguson 536 (3): 667 -- The Journal of Physiology Online Steady-state voltage-dependent inactivation was found to be more extensive with Ca as the charge carrier, as shown by the greater sensitivity to voltage prepulses (Fig 2 Ab, open circles). We next studied the time course of inactivation of HVA currents and the effect of charge carrier. More inactivation was observed using Ca as the charge carrier, indicating that Ca -dependent inactivation plays a role in regulating Ca channel function in subfornical organ (SFO) neurones. jp.physoc.org /cgi/content/full/536/3/667   (1586 words)

Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations Very skewed or non-random X-inactivation patterns were observed in both twins in six of the monozygotic twin pairs and in one of the dizygotic twin pairs. X-inactivation patterns were studied in umbilical cord tissue in 43 monozygotic twin pairs and 24 dizygotic twin pairs. We have tested the hypothesis that contrasting X-inactivation patterns could be a trigger for monozygotic twinning in females. www.osti.gov /energycitations/product.biblio.jsp?osti_id=426131   (1586 words)

Negative charges in the DIII-DIV linker of human skeletal muscle Na+ channels regulate deactivation gating -- Groome et al. 548 (1): 85 -- The Journal of Physiology Online Closed-state fast inactivation was accelerated by D1309R from -100 to -70 mV and by D1309Q from -100 to -90 mV. 7 were used to calculate the delay in the onset to recovery from fast inactivation, as a measure of the rate of the I to C transition. Thus, the effects of mutations at D1309 on steady-state fast inactivation were allosteric whereas the effects of mutations at EE1314,15 were a consequence of alterations in charge content. jp.physoc.org /cgi/content/full/548/1/85   (1586 words)

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