Emerging Roles of Translational Control in Circadian Timekeeping.

A large part of mammalian physiology and behaviour shows regular daily variations. This temporal organisation is driven by the activity of an endogenous circadian clock, whose molecular basis consists of diurnal waves in gene expression. Circadian transcription is the major driver of these rhythms, yet post-transcriptional mechanisms, some of which occur in response to systemic cues and in a tissue-specific fashion, have central roles in ultimately establishing the oscillatory gene expression programme as well. Regulatory control that occurs at the level of translation is emerging as an important player in the generation and modulation of protein accumulation rhythms. As a mechanism, translation lies at a privileged position to integrate genetically encoded rhythmic signals with other, external and internal stimuli, including nutrient-derived cues. In this review, we summarise our current knowledge of how diurnal control of translation affects both bulk protein levels and gene-specific protein biosynthesis. We discuss mechanisms of regulation, in particular with regard to the complex interplay between circadian cycles and feeding/fasting cycles, as well as emerging roles for upstream open reading frames in clock control.