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. 2018 Mar 26;9(4):180. doi: 10.3390/genes9040180

Figure 1.

Figure 1

Simplified pathway of the core Lepidopteran circadian clock. Arrows represent activation. Vertical lines represent inhibition. Gray lines indicate dimer formation. During the day, light activates the blue light photoreceptor CRYPTOCHROME1 (CRY1). CRY1 activation leads to SHAGGY (SGG) tagging TIMELESS (TIM) for degradation by JETLAG (JET). The PERIOD (PER) monomer is tagged for degradation by SLIMB when not bound to TIM. DOUBLETIME (DBT) regulates PER activity through phosphorylation. The PER/TIM heterodimer forms a complex with CRYPTOCHROME2 (CRY2) and enters the nucleus, where PER and CRY2 inhibit the activity of the CLOCK/CYCLE heterodimer. CLK/CYC binds to E-box enhancers to activate transcription. A second feedback loop is comprised of VRILLE (VRI) and PDP1, which bind to the V/P box of the clk promoter cyclically. VRI acts as repressor of clk transcription but PDP1 activates clk transcription. Modified from [29].