Comparison of Wildtype vs. FASPS Mammalian Molecular Clocks

1. Comparison of Wildtype vs. FASPS Mammalian Molecular Clocks By Erin Eppler May 2010 http://www.soundlighthealer.com/images/circadian_clock_1.jpg

2. A Typical Circadian Rhythm • A circadian rhythm has a period of 24-25 hours, approximately one day’s length • The master clock or suprachiasmatic nucleus (SCN) resides within the hypothalamus • When light strikes specialized ganglion cells of the eye, an electrical impulse is sent to the SCN, accelerating the transcription of Per and Cry genes by CLOCK-Baml1 dimers, whose concentrations increase during the subjective night • The cycle is a series of positive and negative feed back loops

3. Legend • Baml1 gene • Baml1 protein • CLOCK gene • CLOCK protein • Per gene • PER protein • Cry gene • CRY protein • Ribosome • Phosphorylating • Unstable PER protein • CylinKinaseε CKIε

4. Ribosomes CKIε During the subjective night concentrations of Baml1 and CLOCK proteins increase. Newly synthesized mRNA is transported from the nucleus to the cytoplasm where it is transcribed into Baml1 and CLOCK proteins. Baml1 CLOCK Per 1 Per 2 Per 3 Cry 1 Cry 2 CKIε Nucleus CKIε Cytoplasm

5. Ribosomes CKIε Baml1 and CLOCK protein dimerize and re-enter the nucleus where they bind to E-boxes on the promoter region of Per and Cry genes, accelerating transcription. Baml1 CLOCK Per 1 Per 2 Per 3 Cry 1 Cry 2 CKIε Nucleus CKIε Cytoplasm

6. Cytoplasm CKIε Movement of proteins out of the nucleus and into the cytoplasm Baml1 Ribosomes CLOCK CKIε Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

7. Cytoplasm CKIε PER proteins that do not form a dimer are susceptible to phosphorylation by CKIε (CyclinKinaseε) making them less stable, leading to their degradation. Baml1 Ribosomes CLOCK CKIε Phosphorylation Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

8. Unstablization of PER proteins Cytoplasm CKIε Baml1 Ribosomes CLOCK CKIε Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

9. Cytoplasm CKIε CRY-PER or PER-PER dimers form in the cytoplasm and transport back into the nucleus. A CRY-PER dimer binds Baml1 and Cry genes, blocking transcription which leads to a negative feedback loop. Baml1 Ribosomes CLOCK Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus CKIε

10. Cytoplasm CKIε Baml1 and CLOCK protein concentrations decrease over time. Baml1 Ribosomes CLOCK Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus CKIε

11. Cytoplasm CKIε Degradation of BAM and CLOCK proteins will eventually prevent transcription of Per and Cry genes Baml1 Ribosomes CLOCK CKIε Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

12. Cytoplasm CKIε Baml1 Ribosomes CLOCK CKIε Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

13. Cytoplasm CKIε PER and CRY concentrations decrease and unblock Baml1 and CLOCK genes, thus restarting the cycle. Baml1 Ribosomes CLOCK CKIε Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus

14. Familial Sleep Phase Syndrome (FASPS) Molecular Clock • Mutation occurs in the PER2 gene • Circadian rhythm is advanced by 4-5 hours

15. CKIε The FASPS mutation causes accelerated nuclear clearance of PER2, but complex formation with CRY1 prevents nuclear export thereby causing nuclear accumulation and protein stabilization Baml1 Ribosomes CLOCK Per 1 Per 2 Per 3 CKIε Cry 1 Cry 2 Nucleus CKIε Cytoplasm