In nature, both the daily changes of light and dark and the concomitant changes in ambient temperature serve as signals to synchronize circadian clocks. In order to understand how these two pathways are integrated on a neuronal and molecular level we initiated studies using only temperature cycles as synchronizing factor (Glaser & Stanewsky, 2005).
We found that both behavioural and molecular rhythms in Drosophila can be synchronized by temperature cycles within the physiological range of the fly (16°C to 29°C). Moreover, we were able to isolate several mutations that specifically interfere with synchronization to temperature cycles and not to light/dark cycles (Figure), demonstrating that the two input-pathways are distinct (Glaser & Stanewsky, 2005). The nocte mutant (for no circadian temperature entrainment) maps to a gene encoding a novel protein of unknown function. Further analysis indicates that nocte function within certain peripheral sensory structures is required for synchronization of the clock neurons within the brain and the behavioural rhythms controlled by these neurons (Sehadova et al., 2009). In contrast to light signals, which can be received by the clock neurons directly (via Cry, see above), temperature input to the brain therefore seems to require a novel periphery-to-brain neuronal pathway. Current research in our lab is aimed to further characterize this pathway by identifying other factors involved. This is done by a combination of candidate approaches, nocte interactions studies, and characterization of newly isolated temperature synchronization mutants.