Circadian Rhythms Flashcards
What experiment figured out that we must have a central circadian clock?
- Had people sleep with and without cues a
- found that in the absence of cues humans still showed a sleep wake cycle, but the cycle was more than 24 hours (about 25 hrs)
What other daily cycles do we have besides sleep/wake? (3)
- Melatonin levels
- Body temp
- Serum control
Where is the central clock?
-In the SCN (suprachiasmatic nucleus)
How do we know where central clock is?
- neurons in the SCN fire action potentials in a 24 hour rhythm
- isolated SCN neurons continue to keep this rhythm
What happens during ablation of SCN?
disrupts wake/sleep cycle in mice
What happens if SCN is transplanted?
transplanted SCN confers time keeping of host to recipient
What is per?
-central component of the clock, which when mutated leads to altered circadian rhythms
Where were mutations in the central clock studied?
in flies
Where is per expressed?
in the SCN
How do per mRNA and protein cycle?
with a 24 hour rhythm (found in various levels throughout the day)
_____ peaks during the day, ____ peaks during the night
mRNA peaks during day, protein peaks during night
per is a ______ factor which means that it controls _______
- transcription
- expression of other genes
What do per and cry form? What is the function?
- heterodimer
- together they inhibit their own expression
What are per and cry turned on by?
- Bmal
- Clk
How is the central clock maintained?
a ~24 hr of cycle of per transcription, translation, degradation
-controlled by negative feedback of per on its own expression
What is the molecular clock composed of?
4 transcription factors in 2 transcriptional networks
What turn Per back on?
Clock + cycle
What does per do at night?
- enters nucleus
- blocks its own expression
What is the non-visual input to the SCN?
-retinal ganglion cells that express the visual pigment melanopsin can detect light (even in the absence of photoreceptor input)
What are the cells of the non-visual input to the SCN?
- intrinsically photosensitive RGCs
- (ipRGCs)
Where do Melanopsin cells/ipRGCs project? How is this determined?
- SCN
- by expressing lacZ gene
What does the lacZ gene generate?
-blue color under melanopsin promoter
What happens when you genetically kill melanopsin cells?
-animals lose entrainment to light
Does melanopsin KO produce the same results as genetically killing melanopsin cells?
- no
- ipRGC can also receive input from photoreceptors in abscence of melanopsin
