1 Sex Chromosome Biology Laboratory, The Francis Crick Institute, London NW1 1AT, UK james.turner@crick.ac.uk.
2 Sex Chromosome Biology Laboratory, The Francis Crick Institute, London NW1 1AT, UK.
3 Department of Integrative Biology and Physiology, Laboratory of Neuroendocrinology of the Brain Research Institute, University of California, Los Angeles, CA 90095-7246, USA.
4 Stem Cell Biology and Developmental Genetics Laboratory, The Francis Crick Institute, London NW1 1AT, UK.