Topic
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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TL;DR: It is found that expression of many genes from the X chromosome decreased, while expression from the autosomes was largely unchanged, indicating that the primary role of the MSL complex is to up-regulate the male X chromosome.
Abstract: A long-standing model postulates that X-chromosome dosage compensation in Drosophila occurs by twofold up-regulation of the single male X, but previous data cannot exclude an alternative model, in which male autosomes are down-regulated to balance gene expression. To distinguish between the two models, we used RNA interference to deplete Male-Specific Lethal (MSL) complexes from male-like tissue culture cells. We found that expression of many genes from the X chromosome decreased, while expression from the autosomes was largely unchanged. We conclude that the primary role of the MSL complex is to up-regulate the male X chromosome.
152 citations
TL;DR: FACL4 is the first gene shown to be involved in nonspecific mental retardation and fatty-acid metabolism, and Analysis of enzymatic activity in lymphoblastoid cell lines from affected individuals of both families revealed low levels compared with normal cells, indicating that both mutations are null mutations.
Abstract: X-linked mental retardation (XLMR) is an inherited condition that causes failure to develop cognitive abilities, owing to mutations in a gene on the X chromosome. The latest XLMR update lists up to 136 conditions leading to 'syndromic', or 'specific', mental retardation (MRXS) and 66 entries leading to 'nonspecific' mental retardation (MRX). For 9 of the 66 MRX entries, the causative gene has been identified. Our recent discovery of the contiguous gene deletion syndrome ATS-MR (previously known as Alport syndrome, mental retardation, midface hypoplasia, elliptocytosis, OMIM #300194), characterized by Alport syndrome (ATS) and mental retardation (MR), indicated Xq22.3 as a region containing one mental retardation gene. Comparing the extent of deletion between individuals with ATS-MR and individuals with ATS alone allowed us to define a critical region for mental retardation of approximately 380 kb, containing four genes. Here we report the identification of two point mutations, one missense and one splice-site change, in the gene FACL4 in two families with nonspecific mental retardation. Analysis of enzymatic activity in lymphoblastoid cell lines from affected individuals of both families revealed low levels compared with normal cells, indicating that both mutations are null mutations. All carrier females with either point mutations or genomic deletions in FACL4 showed a completely skewed X-inactivation, suggesting that the gene influences survival advantage. FACL4 is the first gene shown to be involved in nonspecific mental retardation and fatty-acid metabolism.
152 citations
Journal Article•
TL;DR: X chromosome- and Y chromosome-specific DNA probes were used to study different aspects of the genesis of sex-chromosome monosomy and demonstrated the presence of a Y chromosome or a second X chromosome in three of 33 spontaneous abortions, a level of mosaicism much lower than that reported for live-born Turner syndrome individuals.
Abstract: X chromosome- and Y chromosome-specific DNA probes were used to study different aspects of the genesis of sex-chromosome monosomy. Using X-linked RFLPs, we studied the parental origin of the single X chromosome in 35 spontaneously aborted and five live-born 45,X conceptions. We determined the origin in 35 cases; 28 had a maternal X (Xm) and seven had a paternal X (Xp). There was a correlation between parental origin and parental age, with the Xp category having a significantly reduced mean maternal age by comparison with the Xm group. Studies aimed at detecting mosaicism demonstrated the presence of a Y chromosome or a second X chromosome in three of 33 spontaneous abortions, a level of mosaicism much lower than that reported for live-born Turner syndrome individuals.
151 citations
TL;DR: The results validate the analysis of chorionic villi for direct prenatal diagnosis of the fragile X syndrome and indicate that somatic heterogeneity of the full mutation is established during the very early stages of embryogenesis.
Abstract: The fragile X syndrome, the most common cause of inherited mental retardation, is characterized by unique genetic mechanisms, which include amplification of a CGG repeat and abnormal DNA methylation. We have proposed that 2 main types of mutations exist. Premutations do not cause mental retardation, and are characterized by an elongation of 70 to 500 bp, with little or no somatic heterogeneity and without abnormal methylation. Full mutations are associated with high risk of mental retardation, and consist of an amplification of 600 bp or more, with often extensive somatic heterogeneity, and with abnormal DNA methylation. To analyze whether the latter pattern is already established during fetal life, we have studied chorionic villi from 10 fetuses with a full mutation. In some cases we have compared them to corresponding fetal tissues. Our results indicate that somatic heterogeneity of the full mutation is established during (and possibly limited to) the very early stages of embryogenesis. This is supported by the extraordinary concordance in mutation patterns found in 2 sets of monozygotic twins (9 and 30 years old). While the methylation pattern specific of the inactive X chromosome appears rarely present on chorionic villi of normal females, the abnormal methylation characteristic of the full mutation was present in 8 of 9 male or female chorionic villi analyzed. This suggests that the methylation mechanisms responsible for establishing the inactive X chromosome pattern and the full mutation pattern are, at least in part, distinct. Our results validate the analysis of chorionic villi for direct prenatal diagnosis of the fragile X syndrome.
151 citations
TL;DR: Nondisjunction due to an error at the second meiotic division was associated with a slight reduction in the total number of recombinant events and an abnormal distribution of exchanges and there was no evidence of an increased paternal age in the aneuploids of paternal origin.
Abstract: We investigated the parent and cell division of origin of the additional sex chromosome in 142 males with a 47,XXY constitution and 50 females with a 47,XXX constitution. In 66 of the 47,XXY males the additional chromosome was paternal in origin and in 76 it was maternal in origin, while among the 47,XXX females only 5 had an additional paternal X chromosome, the remaining 45 having an additional maternal chromosome. Among the 107 maternally derived aneuploids for whom it was possible to determine the cell division of origin, 73 were the result of a mat MI error, 24 the result of a mat MII error and 10 the result of a post zygotic mitotic (PZM) error involving the maternal X chromosome. Among those in which the non-disjunction was attributable to an error at the first meiotic division (MI) we observed three different mechanisms of origin. Approximately 30% were associated with complete absence of recombination (nullichiasmate); approximately 24% were associated with a normal number of recombinant events but an abnormal distribution of exchanges (perturbed recombination), while approximately 45% were associated with a normal number and distribution of recombinant events (normochiasmate). Nondisjunction due to an error at the second meiotic division (MII) was associated with a slight reduction in the total number of recombinant events and an abnormal distribution of exchanges. Thus of the four different meiotic mechanisms of origin, three were associated with an abnormal number and/or distribution of exchange events. There was no evidence of an increased paternal age in the aneuploids of paternal origin.(ABSTRACT TRUNCATED AT 250 WORDS)
150 citations