Co-localization of centromere activity, proteins and topoisomerase II within a subdomain of the major human X alpha-satellite array.
(17/1094)
Dissection of human centromeres is difficult because of the lack of landmarks within highly repeated DNA. We have systematically manipulated a single human X centromere generating a large series of deletion derivatives, which have been examined at four levels: linear DNA structure; the distribution of constitutive centromere proteins; topoisomerase IIalpha cleavage activity; and mitotic stability. We have determined that the human X major alpha-satellite locus, DXZ1, is asymmetrically organized with an active subdomain anchored approximately 150 kb in from the Xp-edge. We demonstrate a major site of topoisomerase II cleavage within this domain that can shift if juxtaposed with a telomere, suggesting that this enzyme recognizes an epigenetic determinant within the DXZ1 chromatin. The observation that the only part of the DXZ1 locus shared by all deletion derivatives is a highly restricted region of <50 kb, which coincides with the topo isomerase II cleavage site, together with the high levels of cleavage detected, identify topoisomerase II as a major player in centromere biology. (+info)
Haplotype inference in random population samples.
(18/1094)
Contemporary genotyping and sequencing methods do not provide information on linkage phase in diploid organisms. The application of statistical methods to infer and reconstruct linkage phase in samples of diploid sequences is a potentially time- and labor-saving method. The Stephens-Smith-Donnelly (SSD) algorithm is one such method, which incorporates concepts from population genetics theory in a Markov chain-Monte Carlo technique. We applied a modified SSD method, as well as the expectation-maximization and partition-ligation algorithms, to sequence data from eight loci spanning >1 Mb on the human X chromosome. We demonstrate that the accuracy of the modified SSD method is better than that of the other algorithms and is superior in terms of the number of sites that may be processed. Also, we find phase reconstructions by the modified SSD method to be highly accurate over regions with high linkage disequilibrium (LD). If only polymorphisms with a minor allele frequency >0.2 are analyzed and scored according to the fraction of neighbor relations correctly called, reconstructions are 95.2% accurate over entire 100-kb stretches and are 98.6% accurate within blocks of high LD. (+info)
Megakaryocyte polyploidization is associated with a functional gene amplification.
(19/1094)
It is believed that polyploidy induces an orchestrated increase in gene expression. To know whether all alleles remain functional during megakaryocyte polyploidization, we used a well-established fluorescence in situ hybridization technique which allows one to simultaneously detect pre-mRNAs and assess ploidy level in a single cell. All alleles of GPIIb, GPIIIa, VWF, beta-actin, hsp70, c-mpl, Fli-1, and FOG-1 genes are transcriptionally active in megakaryocytes from 4N to 32N. All X chromosomes in male cells are transcriptionally active but only half of them are transcriptionally active in female megakaryocytes, as revealed by the transcriptional activity of the GATA-1 gene. Nuclear untranslated XIST RNA accumulates on the inactivated X chromosomes, indicating that they are subjected to a normal inactivation process. Altogether, our results demonstrate that megakaryocyte polyploidization results in a functional gene amplification whose likely function is an increase in protein synthesis parallel with cell enlargement. (+info)
X chromosome dosage by quantitative fluorescent PCR and rapid prenatal diagnosis of sex chromosome aneuploidies.
(20/1094)
During the past few years, rapid prenatal diagnosis of chromosome aneuploidies has been successfully achieved by quantitative fluorescent PCR (QF-PCR) amplification of chromosome-specific small tandem repeats (STR). This approach has proven to be very useful in clinical settings, since it allows the detection of major numerical disorders in a few hours after sampling. For the detection of Turner's syndrome (45,X), several highly polymorphic STR on the X chromosome are needed in order to reduce the likelihood that a normal female might be homozygous for all sequences and, consequently, that the test could fail to discriminate between samples retrieved from a Turner's and a normal female fetus. Here we report a new method for rapid and accurate detection of X chromosome copy number in prenatal samples that does not depend on STR heterozygosity. The test is based on QF-PCR amplification of the X-linked HPRT together with the autosomal D21S1411 used as internal control for quantification. In the course of this study, this assay allowed the prenatal diagnosis of a rare case of a normal female homozygous for four selected highly polymorphic X chromosome STR, as well as the assessment of the normal chromosome complement of a fetus homozygous for five chromosome 21 markers. (+info)
Genetic disorders in premature ovarian failure.
(21/1094)
This review presents the genetic disorders associated with premature ovarian failure (POF), obtained by Medline, the Cochrane Library and hand searches of pertinent references of English literature on POF and genetic determinants cited between the year 1966 and February 2002. X monosomy or X deletions and translocations are known to be responsible for POF. Turner's syndrome, as a phenotype associated with complete or partial monosomy X, is linked to ovarian failure. Among heterozygous carriers of the fragile X mutation, POF was noted as an unexpected phenotype in the early 1990s. Autosomal disorders such as mutations of the phosphomannomutase 2 (PMM2) gene, the galactose-1-phosphate uridyltransferase (GALT) gene, the FSH receptor (FSHR) gene, chromosome 3q containing the Blepharophimosis gene and the autoimmune regulator (AIRE) gene, responsible for polyendocrinopathy-candidiasis-ectodermal dystrophy, have been identified in patients with POF. In conclusion, the relationship between genetic disorders and POF is clearly demonstrated in this review. Therefore, in the case of families affected by POF a thorough screening, including cytogenetic analysis, should be performed. (+info)
A novel gene, FAM11A, associated with the FRAXF CpG island is transcriptionally silent in FRAXF full mutation.
(22/1094)
The cytogenetic expression of the FRAXF fragile site is due to an expanded, hypermethylated and unstable CGG repeat in Xq28. Normal individuals have 6-38 triplet repeats while individuals expressing the fragile site have expansions of greater than 300 triplets. Through analysis of the region adjacent to the fragile site, we have identified a approximately 2.6 kb cDNA originating from the FRAXF fragile site associated CpG island, and containing the unstable FRAXF CGG repeat in its 5' UTR region. This gene, FAM11A, comprises at least seven exons, shows alternative splicing, and extends over 35 kb of genomic DNA distal to the FRAXF fragile site. Analysis of the FAM11A cDNA sequence has identified a 1050 bp open reading frame encoding a 350 amino acid protein. We have also identified FAM11B a highly conserved (88% at the protein level) transcribed chromosome 2 retropseudogene. We show that the novel FRAXF fragile site associated gene FAM11A is transcriptionally silenced in a normal individual with a cytogenetically and molecularly detectable FRAXF CGG full mutation (fragile site). Finally, we were able to reactivate FAM11A transcription by treatment of a FRAXF lymphoblastoid cell line with the demethylating agent 5-azadeoxycytidine, thus demonstrating the critical role of FRAXF methylation in FAM11A silencing. (+info)
Analysis of sex chromosomes in preimplantation genetic diagnosis for X-chromosome-linked disorders.
(23/1094)
Preimplantation genetic diagnosis (PGD) is diagnostic tool to avoid inheritance of genetic disease by transferring unaffected embryos. Recently, PCR and FISH have been mainly applied to the diagnosis of single gene disorders and chromosomal abnormalities, respectively. Since with PGD, only a few cells are available for genetic tests, both gene and chromosomes analysis have to be obtained from the same, limited material. Cell recycling makes it possible to obtain the information on genes as well as chromosomes from the same cells. Therefore cell recycling is an acceptable strategy where in PGD targets large proportions of embryos severe chromosomal abnormalities. The responsible genes of the X-linked disorder and numerical abnormalities of sex chromosomes should be analyzed simultaneously. Gender information is definitely useful because only male affected embryos should be avoided for transfer. (+info)
Diabetes mellitus associated with Klinefelter's syndrome: a case report and review in Japan.
(24/1094)
We report a case of Klinefelter's syndrome in a 48-year-old man who had diabetes mellitus associated with severe insulin resistance. We diagnosed him with Klinefelter's syndrome from his atrophic testicles, primary hypogonadism in hormonal examination, and a chromosomal aberration of 47,XXY. He showed severe decreased insulin sensitivity in a hyper-insulinemic euglycemic clamp test. He had injected over 100 units of insulin per day, however, testosterone replacement and administration of pioglitazone improved his glycemic control, which resulted in a decrease of insulin dose to less than 50 units per day. Here, we discuss the characteristics of diabetes mellitus associated with Klinefelter's syndrome in Japanese patients including this case. (+info)