Figure 4.

Induction of the CRTC1-SIK1 Pathway in the SCN in Response to Phase-Shifting Stimuli

(A) Expression data from exon arrays indicating relative levels of Crtc isoforms in the SCN, showing Crtc1 is the most abundant isoform.

(B) CRTC1 (green) translocates from the cytoplasm (upper left, 0 min) to the nucleus (upper right, 10 min) 10 min after the application of 50% horse serum to dissociated SCN cell cultures. Merged figures with DAPI staining (blue, nuclei) and phalloidin (white, cytoskeleton) are indicated in the respective lower panels.

(C) SIK1 protein is increased in the SCN 120 min after a CT16 light pulse, representative blots shown. β-actin levels shown for comparison.

(D) Sik1 was upregulated by light in the SCN of animals after a CT16 phase-delaying and CT22 phase-advancing light pulse, as measured by qPCR (CT16: p = 0.0002 ^∗∗∗, n = 5, CT22: p = 0.009 ^∗∗, n = 3). Egr1 and Nr4a1 levels are shown for comparison, where in contrast, their induction is lower at CT22 than at CT16. Sham = SCN from sham-pulsed mice; LP30, LP60, and LP120 = SCN from 30, 60, and 120 min after light pulse, respectively. Error bars = SEM.