Endogenous Rhythms + Nonphotic Rhythms

Question 1

Non photic phase shifting and entrainment:
- Rusak - Dark pulses in LL
- Ralph/Menaker - GABA agonists
- Turek - Triazolam
- Mrosovsky - Behavioural activation or arousal

Answer 1

Dark pulses in LL cause phase shifts in subjective day

GABA agonists block light induced phase delays
GABA antagonists block light induced phase advances

Dark pulse shifts are mimicked by triazolam (GABA agonist)

Triazolam induced and dark pulse shifts require behavioural activation or arousal
- Changing cage of hamster was an arousing stimulus; causes them to move around more and mark scent

Question 2

If an animal has entrained to a shift from a nonphotic stimulus (dark pulse, new running wheel, etc), how do you reset its effect?

Answer 2

Turn on light in the dark
(Light tells hamster that they need to go home bcuz they are nocturnal)

Question 3

Trypanomosa cruci (kissing bug)
- Nonphotic stimulus -> Subjective day chicken pulse
- Nonphotic stimulus -> Subjective day mechanical disturbance
- Photic entrainment w/ chicken pulse

Answer 3

Caused activity to freerun
Shortened periods and arrhythmic

Induces bug to eat but presence of light prevents entrainment
- No behavioural arousal
- But alters phase angle of entrainment and shortens freerunning period

Question 4

We assume that light/dark cycles provide the primary circadian Zeitbeger, so why is the circadian system resettable by other stimuli?

Answer 4

Direct access to light may be limited

Exposure to light may be too dangerous

Question 5

Social zeitgeber
Problem with this?

Answer 5

Pressure from the population to adapt the individual temporal program to a common program for the population
- Matching of CT to social schedules (like work, school, etc)

Problem: Some people may have adaptive advantageous bio clocks but advantage isn’t shown because of social pressure

Question 6

Circadian clock mechanism has been reinvented how many times?

Answer 6

4-5
Bacteria, fungi, plants, animals, (archaea)

Question 7

Early findings of clock genetics:
Bunning - Innateness
Pittendrigh - Freerunning periods
Konopka/Benzer - Clock mutants

Answer 7

Fruit flies raised in LL causing arrhythmic rhythms, but were re-synced after return to DD

Different species have different freerunning periods

First bonafide clock mutants induced by xray mutagenesis in fruit flies

Question 8

Konopka
Fruit flies and Period (PER)

Answer 8

Selected for fruit flies that came out at wrong time (mutants)
Genetic screen showed mutations were only found on Period gene

Question 9

Dunlap and Loros
Neurospora (fungi) and Frequency (FRQ)

Answer 9

Yellow rings show where fungi stops growing every 12 hours to let out fruit bodies
Mutations in speed of were all found on Frequency gene

Question 10

Young
Timeless gene (TIM)
Double-time

Answer 10

TIM and PER proteins produce a protein dimer, which is a transcription factor
- This causes changes in genes when it re-enters nucleus (mutations)
- Dimer is negative transcription factor that shuts down production of TIM and PER mRNA

Ex: Double-time mutation regulating PER causes lengthening of period in fruit flies
- mRNA oscillations precede protein oscillations

Question 11

Fruit fly molecular clock (transcription translation feedback loop)
TIM/PER
CLK/CLY
Where does light hit?

Answer 11

TIM/PER is negative transcription factor

CLK/CLY is positive transcription factor
- Sends out clock-controlled genes to send info to system

Light impacts TIM and causes it to degrade
- Delays negative transcription feedback

Question 12

Neurospara molecular clock (transcription translation feedback loop)
FRQ/FRQ
WC-1/WC-2
Where does light hit?
What happens if WCC is high in evening and morning?

Answer 12

FRQ/FRQ is negative transcription factor

WC-1/WC-2 is positive transcription factor
- Uses clock-controlled genes to send out info to system

Light impacts WC-1 and increases transcription activity

WCC high in evening - Evening phase genes activated
High in morning - Morning phase genes activated

Question 13

Casein kinases
Ck1,2
Ck1ε

Answer 13

Involved in control of cell morphology

Responsible for short period tau mutation in hamsters and double-time in fruit flies
- Loss of phosphorylation site on mPer2 and mutation responsible for advanced sleep phase syndrome (ASPS) in humans and mice (mutation only tho)

Question 14

Human molecular clock (transcription translation feedback loop)
BMAL1/CLOCK
PER/CRY

Answer 14

PER/CRY is negative transcription factor
BMAL1/CLOCK is positive transcription factor

Light received thru retina, cells send signal to hypothalamus, drives production of 4 genes

Question 15

Kai Clock in cyanobacteria
KaiC
KaiA
KaiB

Answer 15

KaiC - Autophosphorylates and dephosphorylates
KaiA - Promotes phosphorylation during day by binding to A-loop on C2 ring of KaiC
KaiB - Inhibits Kai A during night by binding to B-loop on C1 ring of KaiC

Example of post-transcriptional oscillator

Question 16

Plant molecular clock (transcription translation feedback loop)
TOC1 and CCA1

Answer 16

TOC1 is negative transcription factor
CCA1 is positive transcription factor

Question 17

Cyanobacteria circadian clock output mechanism
SasA
RpaA, class 1 and 2 gene cycle
CikA

Answer 17

SasA binds to KaiC throughout day and gets autophosphorylated
- Transfers phosphate group to RpaA
CikA binds to KaiB throughout night and dephosphorylates RpaA

Phosphorylated RpaA binds to activate class 1 gene transcription factors. Nonphosphorylated version can’t bind.
- Transcription in day, no transcription at night

Phosphorylated RpaA binds to inhibit class 2 gene transcription factors. Nonphosphorylated version can’t bind.
- No transcription in day, transcription at night