Transcriptional initiation of each gene is assumed to be independently 
controlled in mammals. On the other hand, recent large-scale transcriptome 
analyses have shown that the genome is pervasively transcribed, such that the 
most of its DNA gives rise to RNAs. This raises the question of whether it is 
possible to pinpoint and activate a particular locus without perturbing numerous 
neighbouring transcripts. Here we show that intensive transcription at one locus 
frequently spills over into its physical neighbouring loci. Rapid induction of 
immediate-early genes (IEGs) in response to growth factor stimulations is 
accompanied by co-upregulation of their neighbouring genes. Profiling the 
primary transcripts in the nucleus with whole-genome tiling arrays delineated 
simultaneous activation of transcription centred on IEGs. Even in surrounding 
intergenic regions, transcriptional activation took place at the same time. 
Acetylation levels of histone H3 and H4 are elevated along with the IEG 
induction and neighbouring co-upregulation. Inhibition of the mitogen-activated 
protein kinase (MAPK) pathway or the transcription factor SRF suppresses all 
transcriptional upregulation. These results suggest that transcriptional 
activation has a ripple effect, which may be advantageous for coordinated 
expression.