Global changes in gene expression following exposure of murine myoblasts to IGF-1. The number of genes that are either up- or down-regulated following acute exposure of C2C12 myoblasts to IGF-1 is shown (Fig. 1A). More genes are up- than down-regulated by IGF-1 at all the time points studied. Several, early induced genes are transcription factors and few of these are consistently expressed at all times. More genes are induced or repressed at the later times indicating secondary affects on the expression of a larger number of target genes, following the early surge in transcription factor expression. Figures 1 B-C show the temporal pattern of up- and down-regulated genes following exposure of murine myoblasts to IGF-1. Data from Venn diagrams show that several early expressed genes are transcription factors. Only 12 and 2 genes are up- (Fig. 1B) or down-(Fig. 1C) regulated, respectively, at all time points of acute IGF-1 treatment. At least 37 genes are induced at 2 hrs and remain so at 4 hrs. In contrast the expression of only 16 genes is repressed at 2 hrs and this remains so at 4 hrs. A tabulated list of genes for each of these groups is given elsewhere (see Tables 1 and 2 and also Additional files 1 and 2). Genes considered here and in other sections represent a 2-fold or greater change with respect to the zero time point.