The Neurospora circadian clock: simple or complex?

The fungus Neurospora crassa is being used by a number of research groups a s a model organism to investigate circadian (daily) rhythmicity. In this re view we concentrate oil recent work relating to the complexity of the circa dian system in this organism. We discuss: the advantages of Neurospora as a model system for clock studies; the frequency (frq), white collar-1 and wh ite collar-2 genes and their roles in rhythmicity the phenomenon of rhythmi city in null frq mutants and its implications for clock mechanisms; the stu dy Of output pathways using clock-controlled genes; other rhythms in fungi; mathematical modelling of the Neurospora circadian system; and the applica tion of new technologies to the study of Neurospora rhythmicity. We conclud e that there may be many gene products involved in the clock mechanism. the re may be multiple interacting oscillators comprising the clock mechanism, there may be feedback from output pathways onto the oscillator(s) and from the oscillator(s) onto input pathways, and there may be several independent clocks coexisting in one organism. Thus even a relatively simple lower euk aryote call be used to address questions about a complex, networked circadi an system.