| Circadian rhythms are daily biological rhythms that persist in constant conditions. They are regulated by an internal rhythm generator called the circadian clock. Studies in the filamentous fungus Neurospora crassa pioneered the use of molecular genetics to study the circadian clock. The clock is composed of input pathways that signal environmental information to a central oscillator(s) that, in turn, regulates output pathways. The control of output pathways by the circadian clock is one of the least understood areas in chronobiology. N. crassa provides the necessary tools to study output regulation; an oscillator involving that central clock component FRQ, and an output pathway (asexual spore formation, conidiation) have been well described. Once a day in the late night, the N. crassa clock signals the initiation of a developmental switch that results in the production of air dispersible conidiospores. How the N. crassa clock regulates the conidiation pathway, as well as other outputs, is the focus of this research.; The clock impinges early upon the conidiation pathway. Key players of development are regulated in a temporal sequence (aconidiate-2 and fluffy), whereas the clock uniquely regulates other genes associated with the developmental process (ccg-1 and eas(ccg-2)). We show that, rather than the clock simply triggering a rhythmic developmental cascade of gene expression, the clock independently regulates genes involved in the developmental process. To identify candidate genes required for signaling rhythmic development, we used microarrays to identify clock- and developmentally-regulated genes. One of these, a serine-threonine kinase (NRC-2) was found to either directly or indirectly relay temporal information from the FRQ-based oscillator to specific genes involved in the conidiation pathway. Some clock-controlled genes were found to be NRC-2-independent. We hypothesize that an uncharacterized oscillator present within the cell participates in the regulation of the NRC-2-independent clock-controlled genes. |
