X-chromosome inactivation: counting, choice and initiation

Nat Rev Genet. 2001 Jan;2(1):59-67. doi: 10.1038/35047580.


In many sexually dimorphic species, a mechanism is required to ensure equivalent levels of gene expression from the sex chromosomes. In mammals, such dosage compensation is achieved by X-chromosome inactivation, a process that presents a unique medley of biological puzzles: how to silence one but not the other X chromosome in the same nucleus; how to count the number of X's and keep only one active; how to choose which X chromosome is inactivated; and how to establish this silent state rapidly and efficiently during early development. The key to most of these puzzles lies in a unique locus, the X-inactivation centre and a remarkable RNA--Xist--that it encodes.

Publication types

  • Review

MeSH terms

  • Animals
  • Chromosome Mapping
  • Dosage Compensation, Genetic*
  • Drosophila melanogaster / genetics
  • Female
  • Male
  • RNA / genetics
  • RNA, Long Noncoding
  • RNA, Untranslated / genetics*
  • RNA, Untranslated / metabolism*
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism*
  • X Chromosome*


  • RNA, Long Noncoding
  • RNA, Untranslated
  • Transcription Factors
  • XIST non-coding RNA
  • RNA