The binding of activated STAT3 to a STAT3 recognition element (21518 to 21510 bp in relation to the transcription start site) in the mouse GFAP promoter plays a major role in the transcriptional activation of GFAP [53] . Activation of STAT3 was also identified in astrocyte-like cells (Fig. 2B) , which suggested that STAT3 may be responsible for GFAP activation. To test this, the occupancy of activated STAT3 was examined by a ChIP assay, using similar primer sets a-g as shown in Fig. 4A . As anticipated, the occupancy of activated STAT3 was more abundant around the STAT3-binding site at the GFAP promoter (primer sets b and c, especially primer set b at the STAT3 binding site) in differentiated cells compared to undifferentiated cells (Fig. 5A) .