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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.


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Journal ArticleDOI
TL;DR: It is suggested that these differential effects of the X and Y chromosomes on growth explain the expression of sexual dimorphism in various somatic features, such as the size, shape and number of teeth, and, under the assumption of genetic pleiotropy, torus mandibularis, statural growth, and sex ratio.
Abstract: Studies on tooth crown size and structure of individuals with various sex chromosome anomalies and their normal male and female relatives have demonstrated differential direct effects on growth of genes on the human X and Y chromosomes. The Y chromosome promotes growth of both tooth enamel and dentin, whereas the effect of the X chromosome on tooth growth seems to be restricted to enamel formation. Enamel growth is decisively influenced by cell secretory function and dentin growth by cell proliferation. It is suggested that these differential effects of the X and Y chromosomes on growth explain the expression of sexual dimorphism in various somatic features, such as the size, shape and number of teeth, and, under the assumption of genetic pleiotropy, torus mandibularis, statural growth, and sex ratio. Future questions concern, among other topics, the Y chromosome and the mineralization process, concentric control of enamel and dentin growth, and gene expression.

101 citations

Journal Article
TL;DR: It is concluded that X inactivation allows the excessive gain of X chromosomes found in germ-cell-derived tumors of the adult testis and offers an interesting model to study the fundamental mechanisms of these processes.
Abstract: In female mammalian cells, inactivation of one of the X chromosomes compensates the increased dosage of X-linked genes as compared with their male counterparts This process is initiated by the X-inactive specific transcripts of the xist/XIST gene in cis, resulting in methylation of specific sites of genes to be silenced However, in male germ cells, X inactivation is established by xist/XIST expression only We investigated the X inactivation pattern in human testicular tumors of different histogenesis by analysis of XIST expression and methylation of the androgen receptor gene XIST was expressed only in tumors derived from the germ cell lineage with supernumerical X chromosomes: seminomas, nonseminomas, and spermatocytic seminomas Although low expression was present in testicular parenchyma with spermatogenesis, XIST was expressed at a higher level in parenchyma with carcinoma in situ, the precursor lesion of seminomas and nonseminomas Despite the consistent expression of XIST in germ-cell-derived tumors with gain of X chromosomes, methylation of the androgen receptor gene was present in all differentiated but only in a proportion of the undifferentiated nonseminomas This differential pattern of methylation was also found in a number of representative cell lines Our data indicate that the counting mechanism resulting in X inactivation is functional in testicular cancers of different histogenesis Moreover, the differentiation-dependent pattern of X inactivation as reported during normal development in the case of multiple X chromosomes by methylation is retained in these tumors We conclude therefore that X inactivation allows the excessive gain of X chromosomes found in germ-cell-derived tumors of the adult testis In addition, this offers an interesting model to study the fundamental mechanisms of these processes

101 citations

Book ChapterDOI
01 Jan 1998
TL;DR: DNA methylation of the X chromosome is reviewed and discussed, with emphasis on the partial methylation seen in the mouse X-linked Pgk1 promoter region, and chromatin accessibility differences between the active X chromosome (Xa) and the inactive X chromosomes (Xi).
Abstract: DNA methylation of the X chromosome is reviewed and discussed, with emphasis on the partial methylation seen in the mouse X-linked Pgk1 promoter region. A new study of partial methylation is presented in which the methylation of CpG site H3 in the mouse Igf2 upstream region was quantitatively measured during growth of subcloned cells in tissue culture. Before subcloning the average methylation level was 50%. After subcloning, methylation was highly variable in early stage clones. With continued passage, clones initially having high methylation lost methylation, whereas clones initially having low methylation gained methylation. By about the 25th generation, all clones had returned to a steady-state methylation level of 50%. These findings are discussed in the context of epigenetic mechanisms and epigenetic fidelity. Interpretation of the results is made according to a model that assumes stochastic methylation and demethylation, with rate parameters influenced by local chromatin structure. A second type of study is reported in which we have measured chromatin accessibility differences between the active X chromosome (Xa) and the inactive X chromosome (Xi). We found that Xa/Xi differences in accessibility to DNase I are surprisingly labile. Relatively infrequent DNA nicks rapidly eliminate differential accessibility.

101 citations

Journal ArticleDOI
TL;DR: There was good correlation between the pattern of gene silencing and the attenuation of clinical phenotype associated with each partial autosomal trisomy, and the distribution of histone modifications which distinguish the inactive X are more accurate cytogenetic measures of the spread of X inactivation than late-replication.
Abstract: We have performed detailed studies of the spreading of X inactivation in five unbalanced human X;autosome translocations. Using allele-specific RT–PCR we observed long-range silencing of autosomal genes located up to 45 Mb from the translocation breakpoint, directly demonstrating the ability of X inactivation to spread in cis through autosomal DNA. Spreading of gene silencing occurred in either a continuous or discontinuous fashion in different cases, suggesting that some autosomal DNA is resistant to the X inactivation signal. This spread of inactivation was accompanied by, but not dependent upon, CpG island methylation. Observations of late-replication, histone acetylation and histone methylation show that X inactivation can spread in the absence of cytogenetic features normally associated with the inactive X. However, the distribution of histone modifications which distinguish the inactive X are more accurate cytogenetic measures of the spread of X inactivation than late-replication. Overall, despite remarkable variation in the spread of X inactivation among the five cases there was good correlation between the pattern of gene silencing and the attenuation of clinical phenotype associated with each partial autosomal trisomy. We discuss our observations in the context of hypotheses which address the spread of X inactivation.

101 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202372
2022124
2021192
2020179
2019190
2018186