Rhythms of differentiation and diacylglycerol in Neurospora

Although the fungus Neurospora crassa is a relatively simple lower eukaryot e, its circadian system may be more complex than previously thought. In thi s paper we review evidence suggesting that there may be several output path ways coupled in complex ways to a single oscillator, or that there may be m ore than one oscillator driving independent output pathways. We have descri bed two new rhythms in Neurospora that are not tightly coupled to the rhyth m of conidiation bands that is the standard assay for the state of the Neur ospora circadian clock. The first is a rhythm in the timing of differentiat ion, i.e. the production of aerial hyphae and spores, Large regions of the mycelium differentiate synchronously, as if responding to a spatially wides pread signal. This rhythm may be distinct from the timer that sets the dete rmination switch controlling the spatial pattern of conidiation bands. The second new rhythm is an oscillation in the levels of the neutral lipid diac ylglycerol (DAG). This rhythm is found in all regions of a colony and is no t always in phase with the rhythm of conidiation bands. The DAG rhythm shar es some characteristics with the differentiation rhythm and has the potenti al to act as the signal that induces rhythmic differentiation.