Lecture 4

Question 1

Who discovered the first circadian clock gene, and in what year?

Answer 1

Konopka & Benzer discovered the Period mutant in Drosophila flies in 1971.

Question 2

What methodology was used by Konopka & Benzer in 1971 to identify the Period mutant?

Answer 2

Mutagenesis and behavioral tests in Drosophila flies to identify circadian rhythm disruptions.

Question 3

When was the Period gene cloned, and by whom?

Answer 3

The Period gene was cloned in 1984 by Hall, Rosbash, and Young.

Question 4

What was the first mammalian circadian mutant discovered, and who identified it?

Answer 4

The “Tau” hamster, a mammalian circadian mutant, was discovered by Ralph & Menaker in 1988.

Question 5

When and how was the SCN established as the central pacemaker for circadian rhythms?

Answer 5

In 1990, Ralph & Menaker conducted transplant studies, showing that the SCN is the central pacemaker.

Question 6

What circadian clock gene did Takahashi discover in 1997, and why is it significant?

Answer 6

Takahashi discovered the Clock gene, the first circadian clock gene identified in mammals, using mice.

Question 7

What year were the Cry1 and Cry2 genes discovered, and by whom?

Answer 7

Cry1 and Cry2 were discovered in 1999 by Takahashi, Sancar, and van der Horst.

Question 8

What did the discovery of the “Timeless” gene in 1994 reveal about circadian mechanisms?

Answer 8

Discovered by Sehgal & Young, “Timeless” showed that PER and TIM proteins form a complex to regulate transcription in a feedback loop.

Question 9

What experimental approach revealed that clock genes are conserved across all animals?

Answer 9

Genome analysis demonstrated that the basic building blocks of the molecular clock are conserved in all animals.

Question 10

What is the significance of CK1ɛ (Casein Kinase 1 epsilon) in the circadian clock?

Answer 10

CK1ɛ (discovered by Menaker & Takahashi in 2000) targets PER proteins for degradation, influencing the clock’s speed.

Question 11

What is the Transcriptional Translational Feedback Loop (TTFL)?

Answer 11

The TTFL is the core molecular mechanism of the circadian clock, where PER and CRY proteins inhibit their own transcription by forming a complex with CLOCK and BMAL1, creating a feedback loop.

Question 12

How does phosphorylation regulate the molecular clock?

Answer 12

Phosphorylation (e.g., by CK1ɛ) targets PER proteins for degradation, ensuring the feedback loop resets to start a new cycle.

Question 13

What experimental approach helped identify interacting partners in the circadian clock mechanism?

Answer 13

Studies focusing on protein-protein interactions revealed complexes like PER-TIM and CLOCK-BMAL1, which are essential for regulating circadian rhythms.

Question 14

What experimental evidence established the SCN as the central pacemaker?

Answer 14

Lesion studies removing the SCN abolished circadian rhythms, while SCN transplants restored rhythmicity in arrhythmic animals (Ralph & Menaker, 1990).

Question 15

What did the Stephan and Becker (1989) study reveal about food entrainment?

Answer 15

It showed that food entrainment is limited to a circadian range (near 24 hours), providing evidence that food-anticipatory activity is driven by a circadian clock.

Question 16

How were homologous clock genes discovered in mammals?

Answer 16

By cloning genes homologous to the Period gene in flies, researchers identified mammalian counterparts like mPer1/2 and mCry1/2.

Question 17

What did the discovery of Rev-erbs and RORs reveal about circadian regulation?

Answer 17

Rev-erbs act as transcriptional repressors, while RORs act as activators. Together, they regulate Bmal1 expression, fine-tuning the clock.

Question 18

What role does FBXL3 play in the circadian clock?

Answer 18

FBXL3 targets CRY proteins for degradation, helping regulate the stability and period of the circadian feedback loop.

Question 19

How has machine learning contributed to circadian gene discovery?

Answer 19

Machine learning identified rhythmic gene expression patterns, helping uncover new clock modulators and pathways.

Question 20

What are some human health disorders associated with circadian clock gene mutations?

Answer 20

Disorders include Delayed Sleep Phase Syndrome, metabolic syndromes, bipolar disorder, and seasonal affective disorder.

Question 21

What is the significance of the “ClockΔ19” mutation?

Answer 21

The ClockΔ19 mutation disrupts circadian rhythms, leading to arrhythmic behavior in constant conditions and metabolic imbalances.

Question 22

What is the role of Casein Kinase 1 epsilon (CK1ɛ) in the circadian clock?

Answer 22

CK1ɛ phosphorylates PER proteins, targeting them for degradation and controlling the clock’s pace.

Question 23

What is unique about the Tau hamster mutant?

Answer 23

The Tau mutant has a shortened circadian period (20 hours) due to a mutation in CK1ɛ, which accelerates PER protein degradation.

Question 24

What role do Rev-erbs play in metabolism?

Answer 24

Rev-erbs recruit HDAC3 to repress genes involved in lipid and glucose metabolism, linking circadian rhythms to energy homeostasis.