Circadian Rhythms Flashcards
How did we first tell that organisms were able to perceive time?
They saw that Drosophila had a varying locomoter activity alternating periods, that locomotory activity in mice was happening at specific periods, that production of specific hormones in humans were periodic, etc.
What are the 4 possible types of clocks you can have?
Slave model : no intrinsic clock
Entrained autonomous clock
Entrained non-autonomous clock
Autonomous clock
In molluscs, what experiment helped us to prove that some parts of the body were acting like clocks?
They did experiments with eyes of molluscs. When put in the dark, the cycle was still going on, but when they removed literally the eyes from the body, you lost the cycles. However, the eyes, out of the body, were still showing timed activity. They then decided to isolate basal retinal neurons and understood that they were the ones cycling in isolation in the eye, generating the circadian rhythms. Those cycles are mediated by the permeability of the membrane to K+: it is more permeable to K+ before dawn, leading to hyperpolarization.
In Drosophila, what gene seems to be regulating the circadian rhythms and what are the 4 types?
The per gene. It is a diffusible substance.
- WT
- Arrythmic
- short-period of activity
- long period of activity
What is the mammal clock?
It is located in the suprachiasmatic nucleus (SCN): when you cause a lesion there, you get a messed up clock. You can have short period or long periods like in Drosophila.
What is the gene involved in clock in mammals?
The per gene!! It is a transcription factor.
How is the per gene regulated?
It is involved in a feedback loop regulating its own transcription by inhibiting it.
What are the genes involved in the mammal circadian rhythms and their roles (5)?
Period (per) = TF
timeless + Doubletime + per = stable, degraded in nucleus,
clock and cycle = transcriptors = activation of transcription
SHARED IN ALL ORGANISMS (have molecular equivalents)
Are cells of SCN autonomous? Are they synchronized?
They can sense time alone, but they will be unsynchronized if they do so. The cells are synchronous when all interacting together (used luciferase = luminescent). This interaction depends on the synapses of neurons.
In mammals, what structure is driving activity in SCN?
It is the retinal ganglion neurons bearing the melanopsin gene. They respond to light (it is not because of the presence of other cells because they still respond to light without the synaptic input).
What happens if you remove RGCs in mammals?
You get a disrupted circadian rhythm while when you remove cones, it does not disrupt it.
Why are the circadian clock genes expressed in the whole body?
Because those genes are diffusible and their transcription is mediated by the info brought back to SCN by RCGs.
In drosophila, what is the special case of circadian rhythm that is observed?
They have a circadian sensitivity to odors independent of the brain in their antenna regulated by per and timeless genes.
