Nature 351, 406 - 408 (30 May 1991); doi:10.1038/351406a0

X-chromosome inactivation may explain the difference in viability of XO humans and mice

Alan Ashworth, Sohaila Rastan^*, Robin Lovell-Badge^† & Graham Kay^*

Chester Beatty Laboratories, The Institute of Cancer Research,Fulham Road, London SW3 6JB, UK
^* Section of Comparative Biology, MRC Clinical Research Centre, Harrow,Middlesex HA1 3UJ, UK
^† Laboratory of Eukaryotic Molecular Genetics, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK

ONLY about 1% of human XO conceptuses survive to birth and these usually have the characteristics of Turner's syndrome, with a complex and variable phenotype including short stature, gonadal dysgenesis and anatomical defects¹. Both the embryonic lethality and Turner's syndrome are thought to be due to monosomy for a gene or genes common to the X and Y chromosomes². These genes would be expected to be expressed in females from both active and inactive X chromosomes to ensure correct dosage of gene product. Two genes with these properties are ZFX and RPS4X, both of which have been proposed to play a role in Turner's syndrome^3,4. In contrast to humans, mice that are XO are viable with no prenatal lethality (P. Burgoyne, personal communication) and are anatomically normal and fertile. We have devised a system to analyse whether specific genes on the mouse X chromosome are inactivated, and demonstrate that both Zfx and Rps4X undergo normal X-inactivation in mice. Thus the relative viability of XO mice compared to XO humans may be explained by differences between the two species in the way that dosage compensation of specific genes is achieved.

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