Chromosome Research

, 15:147 | Cite as

The region homologous to the X-chromosome inactivation centre has been disrupted in marsupial and monotreme mammals

  • Timothy A. Hore
  • Edda Koina
  • Matthew J. Wakefield
  • Jennifer A. Marshall Graves


Marsupial, as well as eutherian, mammals are subject to X chromosome inactivation in the somatic cells of females, although the phenotype and the molecular mechanism differ in important respects. Monotreme mammals appear to subscribe at least to a form of dosage compensation of X-borne genes. An important question is whether inactivation in these non-eutherian mammals involves co-ordination by a control locus homologous to the XIST gene and neighbouring genes, which play a key regulatory role in human and mouse X inactivation. We mapped BACs containing several orthologues of protein-coding genes that flank human and mouse XIST and genes that lie in the homologous region in chicken and frog. We found that these genes map to two distant locations on the opossum X, and also to different locations on a platypus autosome. We failed to find any trace of an XIST orthologue in any marsupial or monotreme or on any flanking BAC, confirming the conclusion from recent work that non-eutherian mammals lack XIST. We propose the region homologous to the human and mouse X-inactivation centre expanded in early mammals, and this unstable region was disrupted independently in marsupial and monotreme lineages. In the eutherian lineage, inserted and existing sequences provided the starting material for the non-translated RNAs of the X-inactivation centre, including XIST.

Key words

epigenetics marsupials monotremes X-inactivation XIST 

Supplementary material

DO00001119_Fig1_ESM.doc (43 kb)
Fig. 1Human
DO00001119_Fig2a_ESM.pdf (257 kb)
Fig. 2aBase genome: Human
DO00001119_Fig2b_ESM.pdf (243 kb)
Fig. 2bBase genome: Human
DO00001119_Fig3a_ESM.pdf (249 kb)
Fig. 3aBase genome: Mouse
DO00001119_Fig3b_ESM.pdf (242 kb)
Fig. 3bBase genome: Mouse
DO00001119_Fig4_ESM.pdf (4 kb)
Fig. 4Human


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Copyright information

© Springer 2007

Authors and Affiliations

  • Timothy A. Hore
    • 1
  • Edda Koina
    • 1
  • Matthew J. Wakefield
    • 1
    • 2
  • Jennifer A. Marshall Graves
    • 1
  1. 1.ARC Centre for Kangaroo Genomics, Research School of Biological SciencesThe Australian National UniversityCanberraAustralia
  2. 2.Walter and Eliza Hall Institute of Medical ResearchParkville VictoriaAustralia

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