1. Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom;
2. Image Informatics and Computational Biology Unit, Laboratory of Genetics, National Institute on Aging, IRP, NIH Biomedical Research Center, Baltimore MD 21224;
3. Laboratory for Optical and Computational Instrumentation, University of Wisconsin at Madison, Madison, Wisconsin 53706;