The mammalian molecular clockwork controls rhythmic expression of its own input pathway components

Area of Science:

• Chronobiology
• Molecular Biology
• Neuroscience

Background:

• The suprachiasmatic nucleus (SCN) molecular clock synchronizes to light via distinct pathways for dusk and dawn.
• Light during early night causes phase delays via intracellular calcium (Ca2+) release through ryanodine receptors (RyRs).
• Light during late night causes phase advances via guanylyl cyclase activation.

Purpose of the Study:

• To investigate how the core molecular clockwork regulates the availability of photic input pathway components.
• To examine the role of BMAL1 in light resetting mechanisms of the SCN.

Main Methods:

• In situ hybridization, real-time PCR, and immunohistochemistry in wild-type and BMAL1(-/-) mice.
• Luciferase reporter system and transcription assays.
• Two-photon microscopy to measure intracellular calcium concentrations (Ca2+i) in SCN slices.

Main Results:

• BMAL1(-/-) mice showed reduced RyR mRNA and protein levels in the SCN.
• Light-induced mPer expression was impaired during early night in BMAL1(-/-) mice.
• CLOCK::BMAL1 activated RyR expression, while mCRY1 inhibited it; Ca2+i response to caffeine was reduced in BMAL1(-/-) mice.

Conclusions:

• The mammalian molecular clockwork directly influences RyR expression.
• This regulation is crucial for controlling the SCN's photic input pathway.
• Provides the first evidence linking the core clock to its own light-sensing mechanisms.