Profile of microRNA expression in the developing mouse brain. (a) Relative expression levels for the 66 microRNAs that changed significantly (ANOVA, p < 0.001) and more than twofold are shown in five columns corresponding to the five time points. Colors indicate relative signal intensities. The microRNA expression profile was sorted using a hierarchical clustering method, and major clusters are shown ordered according to the time that expression peaks. Gene names and a quantitative description of microRNA expression levels are presented in Additional data file 6. (b) Developmental time points were grouped using the same hierarchical clustering method and gene set as in (a).