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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Human genetics 〈Berlin〉 85 (1990), S. 659-665 
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The inactive fragile×chromosomes of a 47,fra(X),fra(X),Y male with a typical fragile×phenotype were successfully separated from the active homologues by means of somatic cell hybridization. It was shown by FUdR-induction and caffein-posttreatment that the separated inactive×chromosomes expressed their fragile sites and that the presence of an active mutated \sxchromosome was not a prerequisite for fragile X expression. The fragility seems to be an intrinsic property of the individual fragile site. This result is in favour of the classical concept that the fragile site at Xq27.3 has a primary pathogenetic function in this syndrome, although the fragility itself could represent a secondary phenomenon related to an unknown alteration of the DNA in this chromosome region. It is also concluded that inactivation of the fragile\sxchromosome in females is not responsible for either false negative fragile\sxfindings or the observation of fragile\sxnegative colonies isolated from fragile\sxpositive fibroblasts in heterozygotes.
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  • 2
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fragile X syndrome is one of the most common familial causes of mental retardation. It is associated with the expression of a fragile site at Xq27.3, although not all individuals carrying the mutation are fragile-X-positive. Recently, the mutation causing this disease has been identified as the amplification of, or insertion into, a CGG repeat sequence at the fragile site. The mutated chromosome can be recognised by the decrease in mobility of the EcoRI fragment that covers the mutated region. Analysis of lymphocytes of affected males often gives a number of different sized fragments indicating somatic heterogeneity. We have investigated this mosaicism in various tissues of an affected fetus in order to determine the extent of the variation between tissues, and to ascertain how to interpret the results in lymphocytes. Our results suggest that the heterogeneity occurs in all fetal tissues, but that the pattern of fragments observed varies between tissues. Methylation across the region also varies. These differences may be reflected in the cellular phenotypes and may influence the ultimate expression of the clinical phenotype.
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  • 3
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Two females showing partial expression of X-linked chondrodysplasia punctata were identified in a family. Bone dysplasia was caused by an aberrant X chromosome that had an inverse duplication of the segment Xp21.2–Xp22.2 and a deletion of Xp22.3-Xpter. To characterise the aberrant X chromosome, dosage blots were performed on genomic DNA from a carrier using a number of X-linked probes. Anonymous sequences from Xp21.2–Xp22.2 to which probes D2, 99.61, C7, pERT87-15, and 754 bind were duplicated on the aberrant X chromosome. The proposita was heterozygous for all these markers. Dosage blots also showed that the loci for steroid sulfatase and the cell surface antigen 12E7 (MIC2) were deleted as expected from the cytogenetic results. Mouse human cell hybrids were constructed that retained the normal X in the active state. Analysis of these hybrid clones for the markers from Xp21.2–Xp22.2 revealed that all the alleles of the informative markers, present in a single dosage in the genomic DNA, were carried on the normal X chromosome of the proposita. The duplicated X chromosome therefore had two identical alleles, indicating that the aberration resulted from an intrachromosomal rearrangement.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Human genetics 〈Berlin〉 87 (1991), S. 421-424 
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The major concept of fragile X pathogenesis postulates that the fragile site at band Xq27.3 [fra(X)] represents the primary defect. The expression of fra(X) is predicted to be an intrinsic property of the mutated chromosome and, hence, should not be suppressed by X inactivation in females or induced by X-linked trans-acting factors. We made fibroblast clones of a fra(X)-positive female. Monoclonality was demonstrated using the DNA methylation assay at DXS255. The mutated X chromosomes and their states of genetic activity in the different clones were also defined by molecular methods. Five clones were selected to induce expression of fra(X) by 10-7 M FUdR; two carried an active mutated X chromosome, in the other three the mutated X chromosome was inactivated. Fra(X) was found expressed in both types of clones. The percentages of positive cells were as high as 7–10%, regardless of the genetic activity of the mutated X chromosomes. DNA replicating patterns, obtained by BUdR labelling, demonstrated that expression occurred only on the mutated X chromosomes previously identified by molecular methods. The concept that the fragile site represents the primary mutation is now strongly supported by experimental evidence. The expression of fra (X) in females is independent of X inactivation and other trans-acting factors.
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  • 5
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We report the mRNA and protein expression levels of human biglycan (BGN) in patients with different numbers of sex chromosomes. BGN maps to the distal long arm of the X chromosome, band Xq28, near the second pseudoautosomal region. BGN expression levels are reduced in 45,X Turner patients and increased in patients with additional sex chromosomes. This is suggestive of a pseudoautosomal gene or a gene that escapes X inactivation and that has an active Y chromosomal copy. However, we also provide evidence from hybrid cell lines that BGN is subject to X inactivation and that there is no homolog on the Y chromosome. This evidence excludes an escape from X inactivation. Moreover, additional Y chromosomes increase BGN expression levels, despite the absence of a Y chromosomal BGN gene. Therefore, another explanation has to be invoked. The “pseudoautosomal expression” of BGN may be attributed to a gene or genes that escape X inactivation and that regulate the transcriptional activity of BGN. This is the first report concerning an X chromosomal gene that does not show the conventional correlation between gene dosage and expression rate known from other X chromosomal genes.
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  • 6
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] We demonstrate hre that somatic variation of CGG repeat length is based on a mosaic of cells with different but stable FMR–1 alleles and does not reflect permanent mitotic instability. The length of a particular allele in an individual cell was maintained in progeny cells establishing a ...
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  • 7
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Sir — Fragile X syndrome is one of the most frequent forms of congenital mental retardation. Specific molecular abnormalities in affected males were first discovered in 1991 and a gene, FMR1, was cloned subsequently from the fragile site (reviewed in ref. 1). The gene is characterized by ...
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  • 8
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] We report the cloning of a highly conserved pseudoautosomal gene on the human sex chromosomes. A cDNA clone was selected by crosshybridization with a microdissected clone from the chromosomal subregion Xp22.3. It encodes a previously characterized member of the ADP/ATP translocase family and plays ...
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