Is DNA methylation responsible for mammalian X chromosome inactivation?

Miller, Duncan A.; Okamoto, Eri; Erlanger, B.F.; Miller, Orlando J.

doi:10.1159/000131782

Cited by 27 publications

(15 citation statements)

References 4 publications

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“…Wolf and Migeon felt that ubiquitous methylation was not involved in X inactivation and that there is variation in methylation at a given site even in clonally derived cell lines. Our results are in agreement with both of these conclusions and with cytologic observations using anti-5-methylcytosine antibodies that fail to discriminate between active and inactive X chromosomes (26).…”

Section: Discussionsupporting

confidence: 92%

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes.

Yen¹,

Patel²,

Chinault³

et al. 1984

Proc. Natl. Acad. Sci. U.S.A.

195

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Previous theoretical considerations and some experimental data have suggested a role for DNA methylation in the maintenance of mammalian X chromosome inactivation.The isolation of specific X-encoded sequences makes it possible to investigate this hypothesis directly. We have used cloned fragments of the human hypoxanthine phosphoribosyltransferase (HPRT) gene and methylation-sensitive restriction enzymes to study methylation patterns in genomic DNA of individuals with different numbers of X chromosomes and in somatic cell hybrid lines containing human X chromosomes that are either active or inactive or have been reactivated by treatment with 5-azacytidine. The results of these analyses show that there is hypomethylation of active X chromosomes relative to inactive X chromosomes in the 5' region of this gene. In the middle region of the gene, however, a site that is consistently undermethylated on inactive X chromosomes was identified. Taken together, the data suggest that the overall pattern of methylation, rather than methylation of specific sites, plays a role in the maintenance of X chromosome inactivation.

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Section: Discussionsupporting

confidence: 92%

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes.

Yen¹,

Patel²,

Chinault³

et al. 1984

Proc. Natl. Acad. Sci. U.S.A.

195

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Section: Methodsmentioning

confidence: 99%

“…If the increment is similar for inactive X chromosomes, it could not have been detected in the cytological analysis of stained preparations with antibodies specific for m5C (15). By this method, one can apparently detect only a twofold increase (15); in humans, this would correspond to an increase of 4 to 5% m5C (based on the m5C contents observed in human DNA [91). The studies in which HpaII and MspI were used to detect methylation at specific (but undefined) regions of the X chromosome (24) could probably have detected such an increase, but only if most of the methylated sites were CCGG and these were distributed fairly evenly along the X chromosome.…”

Section: Methodsmentioning

confidence: 99%

Relationship of DNA methylation level to the presence of heterochromatin in mealybugs.

Scarbrough¹,

Hattman²,

Nur³

1984

Mol. Cell. Biol.

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Purified nuclear DNA from two mealybug species was analyzed for its 5-methylcytosine (m5C) content by reversed-phase high-pressure liquid chromatography. We observed that the percent m5C (percentage of cytosines which are methylated) varied between the two species, between males and females of the same species, and between lines with and without supernumerary B chromosomes. This is the first case of a sexspecific difference in overall DNA methylation level. In contrast to a recent report (Deobagkar et al., J. Biosci. [India] 4:513-526, 1982), we found no other modified bases in the DNA. Overall, the percent m5C in Pseudococcus obscurius was two to three times higher than in Pseuidococcuis calceolariae. In both species, the percent m5C in males was higher than in females, although only in P. calceolariae was the difference statistically significant (0.68 + 0.02 versus 0.44 ± 0.04). The high m5C content in males was correlated with the presence of a paternally derived, genetically inactive set of chromosomes which is facultatively heterochromatic. The presence of constitutive heterochromatin, however, was associated with a lower m5C content. Thus, for example, the percent m5C in females of a P. obsciurius line with heterochromatic B chromosomes (1.09 ± 0.04) was significantly lower than that of a related line lacking such chromosomes (1.26 ± 0.06). Our findings are discussed with respect to the possible relationship between DNA methylation and heterochromatization.Heterochromatin is characterized by well-known cytological alterations in the appearance and behavior of chromosomes; e.g., heterochromatin appears to be more highly condensed during most of the cell cycle and to replicate later than euchromatin. Also, heterochromatin is generally genetically nonfunctional. Certain chromosome regions (or even whole chromosomes) are constitutively heterochromatic, e.g., centromeric heterochromatin. In contrast, certain chromosomes (regions) may be either euchromatic or heterochromatic, depending upon their origin, number of homologs present, growth stage, and cell type. This facultative heterochromatization is developmentally regulated and may be reversible (17).In mammals, facultative heterochromatization is exemplified by the well-known case of X chromosome inactivation (14). Among the insects, one of the best-known examples is the mealybug, or lecanoid, chromosome system (3). In this system, both males and females start development as diploids with euchromatic chromosome complements. In males, however, the paternally derived set of chromosomes becomes heterochromatic during early embryogeny; it remains heterochromatic in most tissues and appears to be transcriptionally inactive. During spermatogenesis, the heterochromatic set is eliminated and only the maternally derived (euchromatic) chromosome set is included in the sperm. In contrast, both chromosome sets remain euchromatic and genetically functional in females, and both are transmissible during sexual reproduction. Gender is apparently determined by whether the e...

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“…For example. 5-AC induces the activation of the X-linked hypoxanthine phosphoribosyltransferase gene (13), but no differences could be detected in the extent of DNA methylation between active and inactive Xlinked sequences by as sensitive a method as fixation of 5-methylcytosine (5-meCy)-directed antibodies (16). The possibility thus remains that 5-AC may additionally act through another, as yet unknown, mechanism which is distinct from DNA hypomethylation and is equally able to account for the striking properties of this drug.…”

mentioning

confidence: 99%

High-frequency conversion to a "fluffy" developmental phenotype in Aspergillus spp. by 5-azacytidine treatment: evidence for involvement of a single nuclear gene.

Tamame¹,

Antequera²,

Villanueva³

et al. 1983

Mol. Cell. Biol.

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Transient exposure of mycelia from Aspergillus niger and Aspergillus nidulans to the cytidine analog 5-azacytidine, leading to no more than 0.3 to 0.5% substitution for cytosine by 5-azacytosine in A. nidulans DNA, resulted in the conversion of a high fraction of the cell population (more than 20%) to a mitotically and meiotically stable "fluffy" developmental phenotype. The phenotypic variants are characterized by the developmentally timed production of a profuse fluffy network of undifferentiated aerial hyphae that seem to escape signals governing vegetative growth. Genetic analysis with six different fluffy clones reveals that this trait is not cytoplasmically coded, is recessive in heterozygous diploids but codominant in heterokaryons, and exhibits a 1:1 Mendelian segregation pattern upon sexual sporulation of heterozygous diploids. Complementation and mitotic haploidization studies indicated that all variants are affected in the same gene, which can be tentatively located on chromosome VIII of A. nidulans. Molecular analysis to search for modified bases showed that DNA methylation is negligible in in both A. niger and A. nidulans and that no differences could be detected among DNAs from wild-type cells, fluffy clones, or mycelia exposed to 5-azacytidine. It thus appears that high-frequency conversion of fungal mycelia to a stable, variant developmental phenotype by 5-azacytidine is the result of some kind of target action on a single nuclear gene and that this conversion can occur in organisms virtually devoid of DNA methylation.

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Is DNA methylation responsible for mammalian X chromosome inactivation?

Cited by 27 publications

References 4 publications

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes.

Differential methylation of hypoxanthine phosphoribosyltransferase genes on active and inactive human X chromosomes.

Relationship of DNA methylation level to the presence of heterochromatin in mealybugs.

High-frequency conversion to a "fluffy" developmental phenotype in Aspergillus spp. by 5-azacytidine treatment: evidence for involvement of a single nuclear gene.

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