1 Deanery of Biomedical Sciences, Edinburgh Medical School, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9AG, UK.
2 Department of Biology, Section for Cell and Neurobiology, University of Copenhagen, Copenhagen DK-2100, Denmark.
3 Deanery of Biomedical Sciences, Edinburgh Medical School, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9AG, UK. Electronic address: Barry.Denholm@ed.ac.uk.