The clock in the cell: Entrainment of the circadian clock in Neurospora crassa

Since reports of daily leaf movements 2000 years ago, a so-called circadian clock (‘circa diem’ meaning ‘about a day’) has been described in organisms from almost all phyla. The work presented in this thesis gives special emphasis on the circadian clock in the fungus Neurospora crassa, a rather simple cellular system. Neurospora was used to elucidate basic clock mechanisms are that are comparable to those in more complex organisms. To that end, we investigated chronoecological questions as well as questions concerning cellular mechanisms. A worldwide collection of Neurospora crassa strains from the wild was chronotyped and researched on how the circadian clock is related to the latitude of origin. We found correlations in some but not all cases dependent on the zeitgeber (light or temperature) applied. Furthermore, we found –here and also in several other experiments- that phase of entrainment and period are not always correlated. This speaks for encoding of these clock characteristics at different locations in the circadian system: different chronotypes can be the result of different period lengths but also of alterations in inputs or the coupling of outputs to the oscillator. Only few components of circadian clocks are known to date. To find novel clock genes, we applied two methods, one where in a QTL-analysis clock gene candidates can be found with help of the cosegregating circadian phenotypes and another, where a candidate clock gene is mutated. Here, a lack of cryptochrome leads almost exclusively to a delayed chronotype, suggesting it being a clock gene.