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© The Rockefeller University Press, 0021-9525/1999//1399 $5.00
The Journal of Cell Biology, Volume 147, Number 7, , 1999 1399-1408

Original Article

Histone Macroh2a1.2 Relocates to the Inactive X Chromosome after Initiation and Propagation of X-Inactivation



Jacqueline E. Mermouda, Carl Costanzib, John R. Pehrsonb, and Neil Brockdorffa

a X-Inactivation Group, Medical Research Council Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, London W12 0NN, United Kingdom
b Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
MRC Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Rd., London W12 0NN, United Kingdom.44-181-383-830344-181-383-8278

jmermoud{at}hgmp.mrc.ac.uk

The histone macroH2A1.2 has been implicated in X chromosome inactivation on the basis of its accumulation on the inactive X chromosome (Xi) of adult female mammals. We have established the timing of macroH2A1.2 association with the Xi relative to the onset of X-inactivation in differentiating murine embryonic stem (ES) cells using immuno-RNA fluorescence in situ hybridization (FISH). Before X-inactivation we observe a single macroH2A1.2-dense region in both undifferentiated XX and XY ES cells that does not colocalize with X inactive specific transcript (Xist) RNA, and thus appears not to associate with the X chromosome(s). This pattern persists through early stages of differentiation, up to day 7. Then the frequency of XY cells containing a macroH2A1.2-rich domain declines. In contrast, in XX cells there is a striking relocalization of macroH2A1.2 to the Xi. Relocalization occurs in a highly synchronized wave over a 2-d period, indicating a precisely regulated association. The timing of macroH2A1.2 accumulation on the Xi suggests it is not necessary for the initiation or propagation of random X-inactivation.

Key Words: histones • X inactive specific transcript (Xist) RNA • X chromosome inactivation • differentiation • nuclear structure

© 1999 The Rockefeller University Press

Abbreviations used in this paper: DAPI, 4,6-diamidino-2-phenylindole dihydrochloride; EB, embryonic body; ES, embryonic stem; FISH, fluorescence in situ hybridization; LDH, lactate dehydrogenase; LIF, leukemia inhibitory factor; MCB, macrochromatin body; TR, Texas red; Xa, active X chromosome; Xi, inactive X chromosome; Xist, X inactive specific transcript.


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