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.

Aberrant patterns of X chromosome inactivation in bovine clones.

Abstract: In mammals, epigenetic marks on the X chromosomes are involved in dosage compensation. Specifically, they are required for X chromosome inactivation (XCI), the random transcriptional silencing of one of the two X chromosomes in female cells during late blastocyst development. During natural reproduction, both X chromosomes are active in the female zygote. In somatic-cell cloning, however, the cloned embryos receive one active (Xa) and one inactive (Xi) X chromosome from the donor cells. Patterns of XCIhave been reported normal in cloned mice, but have yet to be investigated in other species. We examined allele-specific expression of the X-linked monoamine oxidase type A (MAOA) gene and the expression of nine additional X-linked genes in nine cloned XX calves. We found aberrant expression patterns in nine of ten X-linked genes and hypomethylation of Xist in organs of deceased clones. Analysis of MAOA expression in bovine placentae from natural reproduction revealed imprinted XCI with preferential inactivation of the paternal X chromosome. In contrast, we found random XCI in placentae of the deceased clones but completely skewed XCI in that of live clones. Thus, incomplete nuclear reprogramming may generate abnormal epigenetic marks on the X chromosomes of cloned cattle, affecting both random and imprinted XCI.

Genome-wide analysis of cancer/testis gene expression

Abstract: Cancer/Testis (CT) genes, normally expressed in germ line cells but also activated in a wide range of cancer types, often encode antigens that are immunogenic in cancer patients, and present potential for use as biomarkers and targets for immunotherapy. Using multiple in silico gene expression analysis technologies, including twice the number of expressed sequence tags used in previous studies, we have performed a comprehensive genome-wide survey of expression for a set of 153 previously described CT genes in normal and cancer expression libraries. We find that although they are generally highly expressed in testis, these genes exhibit heterogeneous gene expression profiles, allowing their classification into testis-restricted (39), testis/brain-restricted (14), and a testis-selective (85) group of genes that show additional expression in somatic tissues. The chromosomal distribution of these genes confirmed the previously observed dominance of X chromosome location, with CT-X genes being significantly more testis-restricted than non-X CT. Applying this core classification in a genome-wide survey we identified >30 CT candidate genes; 3 of them, PEPP-2, OTOA, and AKAP4, were confirmed as testis-restricted or testis-selective using RT-PCR, with variable expression frequencies observed in a panel of cancer cell lines. Our classification provides an objective ranking for potential CT genes, which is useful in guiding further identification and characterization of these potentially important diagnostic and therapeutic targets.

Lissencephaly and other malformations of cortical development: 1995 update.

Abstract: Neuronal migration disorders are a group of malformations of the brain which primarily affect development of the cerebral cortex. The best known of these is lissencephaly (smooth brain). Most types result from incomplete neuronal migration to the cortex during the third and fourth months of gestation. In this review, we describe and illustrate the different types of neuronal migration disorders. We also review the many different genetic syndromes associated with neuronal migration disorders. Over 25 syndromes with lissencephaly or other neuronal migration disorders have been described. Among them are syndromes with several different patterns of inheritance including chromosomal or new mutation autosomal dominant, autosomal recessive, X-linked and unknown. Genetic counseling thus differs greatly between syndromes. The genes responsible for several of the lissencephaly syndromes have been mapped. X-linked lissencephaly has tentatively been mapped to chromosome Xq22 based on observation of a single X-autosomal translocation in a girl. Both Miller-Dieker syndrome and isolated lissencephaly sequence (in many patients) were mapped to chromosome 17p13.3 by detection of deletions and other structural chromosome rearrangements. Fukuyama congenital muscular dystrophy was mapped to chromosome 9q31-33 by homozygosity mapping.