Figure 5. Photoentrainment of clock gene and Aanat transcript rhythms

Cell cultures were prepared as described in Methods culture dishes from the same batch of cells were divided into two groups: one kept in incubators without illumination and the other in incubators with a daily light-dark (LD) cycle. Other than exposure to LD, the culture conditions and schedule of medium changes were identical for all cultures. Cultures were sampled on day in vitro (DIV) 8 at ZT 12 and ZT 20 for LD cultures and on DIV 8 at the same times of day for cultures kept in the incubators without illumination. Relative levels of Bmal1, Npas2, and Aanat transcripts were measured. A: Cells cultured under a daily cycle of light and darkness from DIV 0-8 displayed significant differences between zeitgeber times (ZT) 12 and ZT 20 for all three transcripts, with Bmal1 and Npas2 higher at ZT 12 and Aanat higher at ZT 20 (asterisk indicates p<0.01; n=6). B: Cells incubated without a daily cycle of illumination, but treated identically otherwise, displayed no significant difference between the two times of day for any of the transcripts measured; n=5-6.