Regulated genes can be grouped into six clusters based on developmental regulation patterns. The number of genes in each cluster is indicated in the schematic diagram. (a, b) Clusters 1 and 2 represent genes that are predominantly regulated at metamorphic climax, with the former following the endogenous T3 concentration. (c, d) Clusters 3 and 4 include genes with higher levels of expression in tadpoles and frogs (larval- and adult-enriched genes), respectively. (e, f) Clusters 5 and 6 are genes up- or down-regulated mainly at stage 58. All clusters were evaluated by GO analysis and two or more examples of the significantly regulated GO categories that had >60 genes (clusters 1 and 2) and >5 genes (clusters 3 to 6) regulated during metamorphosis are listed. A complete list of GO categories associated with each cluster is listed in Table S6 in Additional file 1. PCA: principal component analysis.