X chromosome

About: X chromosome is a research topic. Over the lifetime, 9862 publications have been published within this topic receiving 407354 citations. The topic is also known as: GO:0000805 & chrX.

Organization and mapping of a sequence on the Drosophila melanogaster X and Y chromosomes that is transcribed during spermatogenesis.

Abstract: The D. melanogaster DNA segment in the recombinant phage λDm2L1 contains at least eight copies of a tandemly repeated 1250-base pair (bp) sequence (henceforth called the 2L1 sequence). Testes from XO D. melanogaster males contain an abundant 800-base RNA species that is homologous to a 520-bp region of the 2L1 sequence. Blotting experiments show that the 2L1 sequence is repeated in the D. melanogaster genome and is present on both the X and Y chromosomes. With the use of X-Y translocations, the 2L1 sequence has been mapped to a region between kl-1 and kl-2 on the long arm of the Y chromosome. In Oregon-R wild type there are an estimated 200 copies of the 2L1 sequence on the X chromosome and probably at least 80 copies on the Y chromosome. In some other strains the repetition frequency on the Y chromosome is about the same, but the copy number on the X chromosome is much reduced. On the basis of the five strains investigated, there is a correlation between copy number of the 2L1 sequence on the X chromosome and the presence of a particular allele of the Stellate locus (Ste; 1-45.7). It seems that low copy number corresponds to Ste + and high copy number corresponds to Ste. The Ste locus determines whether single or star-shaped crystals are observed in the spermatocytes of XO males. Studies using D. simulans and D. mauritiana DNA show that the 2L1 sequence is homologous to restriction fragments in male DNA but not female DNA, indicating that this sequence is present only on the Y chromosome in these two species. In DNA derived from D. erecta, D. teissieri and D. yakuba, there is very little, if any, hybridization with the 2L1 sequence probe.

The distribution of chromosomal genotypes associated with Turner's syndrome: livebirth prevalence rates and evidence for diminished fetal mortality and severity in genotypes associated with structural X abnormalities or mosaicism

Abstract: The proportions of chromosomal genotypes associated with the Turner syndrome genotype (excluding those with a Y chromosome) in embryonic and fetal deaths, in fetuses diagnosed prenatally, and in living individuals were reviewed. The ratio of apparent non-mosaic 45,X to 45,X/46,XX mosaics was notably higher in a New York City series of embryonic and fetal deaths, 13.5 to 1, than in living individuals reported to the New York State Chromosome Registry, 3.6 to 1. The ratios of 45,X cases to those with 46,Xi(Xq) was 5.7 to 1 in living individuals, but was 112 to 0 in embryonic and fetal deaths, an even greater disparity, indicating the marked fetoprotective effect of more than one dose of some locus or loci on the long arm of the X chromosome. The results of review of data pertinent to the livebirth prevalence of the (apparent non-mosaic) 45,X geno-type suggest a rate of about 5.7 per 100,000 livebirths (11.8 per 100,000 females) with 95% confidence limits of 2.6 per 100,000 to 10.8 per 100,000. The rate in fetuses diagnosed prenatally is 8/27,202, about 30 per 100,000. As a large proportion of these, perhaps 75%, would undergo spontaneous fetal death if not terminated electively, these figures are consistent with the direct estimate of livebirth rates. The rate of all those with X chromosome abnormalities (without a Y chromosome) associated with signs or symptoms that eventually lead to referral for cytogenetic study was estimated at a minimum of 10.7 per 100,000 livebirths, (22.2 per 100,000 females).

Localization of the X inactivation centre on the human X chromosome in Xq13

Abstract: X-CHROMOSOME inactivation results in the strictly cis-limited inactivation of many but not all genes on one of the two X chromosomes during early development in somatic cells of mammalian females1. One feature of virtually all models of X inactivation is the existence of an X-inactivation centre (XIC) required in cis for inactivation to occur2–5. This concept predicts that all structurally abnormal X chromosomes capable of being inactivated have in common a defineable region of the X chromosome6–8. Here we report an analysis of several such rearranged human X chromosomes and define a minimal region of overlap. The results are consistent with models invoking a single XIC and provide a molecular foothold for cloning and analysing theXIC region. One of the markers that defines this region is theXIST gene9, which is expressed specifically from inactive, but not active, X chromosomes. The localization of the XIST gene to theXIC region on the human X chromosome implicates XIST in some aspect of X inactivation.

Detection of deletions spanning the Duchenne muscular dystrophy locus using a tightly linked DNA segment

Abstract: The Duchenne muscular dystrophy (DMD) locus has been localized to the short arm of the human X chromosome (Xp21) by detection of structural abnormalities and by genetic linkage studies A library highly enriched for human DNA from Xp21 was constructed using DNA isolated from a male patient who had a visible deletion and three X-linked disorders (DMD, retinitis pigmentosa and chronic granulomatous disease) Seven cloned DNA probes from this library and the probe 754 (refs 5, 8) are used in the present study to screen for deletions in the DNA isolated from 57 unrelated males with DMD Five of these DMD males are shown to exhibit deletions for one of the cloned DNA segments and at least 38 kb of surrounding DNA In addition, two subclones from the same region detect four restriction fragment length polymorphisms which exhibit no obligate recombination with DMD in 34 meiotic events These new DNA segments will complement the existing Xp21 probes for use in carrier detection and prenatal diagnosis of DMD Elucidation of the end points of the five deletions will help delineate the extent of the DMD locus and ultimately lead to an understanding of the specific sequences involved in DMD

Chromodomains are protein–RNA interaction modules

Abstract: In Drosophila, compensation for the reduced dosage of genes located on the single male X chromosome involves doubling their expression in relation to their counterparts on female X chromosomes1. Dosage compensation is an epigenetic process involving the specific acetylation of histone H4 at lysine 16 by the histone acetyltransferase MOF2,3,4,5. Although MOF is expressed in both sexes, it only associates with the X chromosome in males. Its absence causes male-specific lethality6. MOF is part of a chromosome-associated complex comprising male-specific lethal (MSL) proteins and at least one non-coding roX RNA7. How MOF is integrated into the dosage compensation complex is unknown. Here we show that association of MOF with the male X chromosome depends on its interaction with RNA. MOF specifically binds through its chromodomain to roX2 RNA in vivo. In vitro analyses of the MOF and MSL-3 chromodomains indicate that these chromodomains may function as RNA interaction modules. Their interaction with non-coding RNA may target regulators to specific chromosomal sites.