Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): In situ hybridizations showing the severe hypomyelination in spinal cords of 2-week-old transgenic mice that ectopically express Sox4 in oligodendrocytes compared to the wild type. Blue and orange colors were assigned to the originally black-and-white pictures, with the hybridization signal shown as orange on a blue background for the wild type and as blue on an orange background for the transgenic spinal cord. Each in situ hybridization is shown three times, Pop Art style. (See related article on p. 5316.)