Affymetrix probesets in the different k-means clusters shown in Additional data file 2 were compared with Affymetrix MG-430 2.0 probe sets for over-representation of gene categories, using the DAVID (Database for Annotation, Visualization, and Integrated Discovery) functional annotation tool. The Category column shows the original database/resource from which the terms originate. The Term column indicates enriched terms associated with the gene list. The n column indicates the number of genes involved in the term. The expression analysis systematic explorer (EASE) score is a modified Fisher exact P value . BP, biological process; GO, Gene Ontology.