Comparison of Wildtype vs. FASPS Mammalian Molecular Clocks

By Erin EpplerMay 2010

http://www.soundlighthealer.com/images/circadian_clock_1.jpg

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

•

Legend• Baml1 gene

• Baml1 protein

• CLOCK gene

• CLOCK protein

• Per gene

• PER protein

• Cry gene

• CRY protein

• Ribosome

• Phosphorylating

• Unstable PER protein

• Cylin Kinase ε 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.

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Baml1 and CLOCK protein dimerize and re-enter the nucleus where they bind to E-boxes on the promoterregion of Per and Cry genes, accelerating transcription.

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIεMovement of proteins out of the nucleus and

into the cytoplasm

PER proteins that do not form a dimer are susceptible to phosphorylation by CKIε (Cyclin Kinase ε) making them less stable, leading to their degradation. Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Phosphorylation

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Unstablization of PER proteins

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.

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Baml1 and CLOCK protein concentrations decrease over time.

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Degradation of BAM and CLOCK proteins will eventually prevent transcription of Per and Cry genes

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

PER and CRY concentrations decrease and unblock Baml1 and CLOCK genes, thus restarting the cycle.

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε

Familial Sleep Phase Syndrome (FASPS) Molecular Clock

• Mutation occurs in the PER2 gene

• Circadian rhythm is advanced by 4-5 hours

The FASPS mutation causes accelerated nuclear clearance of PER2, but complex formation with CRY1 prevents nuclear export thereby causing nuclear accumulation and protein stabilization

Cytoplasm

Nucleus

Baml1

Per 1

Ribosomes

CLOCK

Cry 1Cry 2

Per 2Per 3

CKIε

CKIε

CKIε