Journal Article

Unbalanced X;autosome translocations provide evidence for sequence specificity in the association of XIST RNA with chromatin

Lisa L. Hall, Christine M. Clemson, Meg Byron, Karen Wydner and Jeanne B. Lawrence

in Human Molecular Genetics

Volume 11, issue 25, pages 3157-3165
Published in print December 2002 | ISSN: 0964-6906
Published online December 2002 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/11.25.3157
Unbalanced X;autosome translocations provide evidence for sequence specificity in the association of XIST RNA with chromatin

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Whether XIST RNA is indifferent to the sequence content of the chromosome is fundamental to understanding its mechanism of chromosomal inactivation. Transgenic Xist RNA appears to associate with and inactivate an entire autosome. However, the behavior of XIST RNA on naturally occurring human X;autosome translocations has not been thoroughly investigated. Here, the relationship of human XIST RNA to autosomal chromatin is investigated in cells from two patients carrying X;autosome translocations in the context of almost complete trisomy for the involved autosome. Since trisomies of either 14 or 9 are lethal in early development, the lack of serious phenotypic consequences of the trisomy demonstrates that the translocated autosomes had been inactivated. Surprisingly, our analyses show that in primary fibroblasts from adult patients, XIST RNA does not associate with most of the involved autosome even though the bulk of it exhibits other hallmarks of inactivation beyond the region associated with XIST RNA. While results show that XIST RNA can associate with human autosomal chromatin to some degree, several observations indicate that this interaction may be unstable, with progressive loss over time. Thus, even where autosomal inactivation is selected for rather than against, there is a fundamental difference in the affinity of XIST RNA for autosomal versus X chromatin. Based on these results we propose that even autosomal chromatin that had been inactivated earlier in development may undergo a stepwise loss of inactivation hallmarks, beginning with XIST RNA. Hence compromised interaction with XIST RNA may be a primary cause of incomplete or unstable autosomal inactivation.

Journal Article.  7042 words.  Illustrated.

Subjects: Genetics and Genomics

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