The neurospora circadian system.

Area of Science:

• Chronobiology
• Molecular Biology
• Mycology

Background:

• Neurospora crassa is a model organism for studying circadian rhythms.
• Pioneering genetic studies identified key clock genes, including frequency (frq).
• Decades of research have elucidated a core molecular feedback loop governing circadian oscillations.

Purpose of the Study:

• To detail the molecular mechanisms of the core circadian clock feedback loop in Neurospora crassa.
• To explain the roles of White Collar (WC)-1, WC-2, and FRQ proteins in circadian regulation.
• To describe how light and temperature influence circadian resetting.

Main Methods:

• Genetic analysis of clock genes.
• Molecular cloning of the frequency (frq) gene.
• Biochemical studies on protein interactions and post-translational modifications (phosphorylation, ubiquitination).

Main Results:

• The White Collar-1 (WC-1)/WC-2 heterodimer functions as both a photoreceptor and a transcription factor, promoting frq gene expression.
• FRQ protein dimerizes, negatively feeds back to inhibit WC-1/WC-2 activity, and positively feeds forward to enhance WC-1 synthesis.
• Phosphorylation and ubiquitination of FRQ lead to its degradation, enabling the restart of the circadian cycle.
• Light rapidly induces frq expression, while elevated temperatures increase FRQ levels, contributing to clock resetting.
• FRQ- and WC-independent oscillators (FLOs) regulate growth and development, coordinated by the core clock.

Conclusions:

• The FRQ/WC complex forms a robust transcription/translation-based negative feedback loop essential for circadian rhythmicity in Neurospora.
• This core loop integrates light and temperature signals to ensure accurate temporal regulation.
• The core clock coordinates downstream clock-controlled genes and FRQ-less oscillators, maintaining overall circadian system function.