A region of euchromatin coincides with an extensive tandem repeat on the mouse (Mus musculus) inactive X chromosome
Euchromatic features are largely absent from the human inactive X chromosome (Xi), with the exception of several large tandem repeats that can be detected as euchromatin bands at metaphase. Despite residing megabases apart, these tandem repeats make frequent inactive X-specific interactions. The mouse homologue has been reported for at least one of the tandem repeats, but whether the mouse Xi is also characterized by distinct bands of euchromatin remains unknown. We examined the mouse Xi for the presence of euchromatin bands by examining the pattern of histone H3 dimethylated at lysine 4 and detected two major signals. The first band resides in the subtelomeric region of band XF5 and may correspond to the pseudoautosomal region. The second band localizes to XE3 and coincides with an extensive complex repeat composed of a large tandem and inverted repeat segment as well as several large short interspersed nuclear element (SINE)-rich tandem repeats. Fluorescence in situ hybridization reveals that sequences with homology to the repeat region are scattered along the length of the Y chromosome. Immunofluorescence analysis of histone H3 trimethylated at lysine 9 on metaphase chromosomes indicates that the repeat region corresponds to a band of constitutive heterochromatin on the male X and female active X chromosomes, whereas the euchromatin signal appears to be female specific. These data suggest that the band of euchromatin observed at XE3 is unique to the mouse Xi, comparable to the chromatin arrangement of several large tandem repeats located on the human X chromosome.
KeywordsInactive X chromosome H3K4me2 Tandem repeat Mouse X chromosome Euchromatin and heterochromatin
Amplified spermatogenic transcripts X encoded
Bacterial artificial chromosome
Bovine serum albumin
Fluorescence in situ hybridization
Histone H3 dimethylated at lysine 4
Histone H3 trimethylated at lysine 9
Histone H3 trimethylated at lysine 27
Long noncoding RNA
Long interspersed nuclear element
Long terminal repeat
Ribosomal protein S12
Short interspersed nuclear element
Serine-rich secreted X-linked
Vomeronasal 2 receptor 121
Active X chromosome
X chromosome inactivation
Inactive X chromosome
X inactivation center
X inactive-specific transcript
This work was supported by the National Institutes of Health [GM073120 to B.P.C.].
Experiments performed in this manuscript comply with the current laws of the USA.
Conflict of interest
The authors declare they have no conflict of interest.
This article does not contain any studies with human or animal subjects performed by any of the authors.
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