In recent work we were able to show that the splicing factor U2AF26 is highly expressed in activated T cells and mouse brain and is itself alternatively spliced. Based on this initial observation we found that U2AF26 isoform expression in the brain is strongly regulated with the circadian rhythm, with a particular splice variant being only present at certain Zeitgeber times. We could then show that this U2AF26 variant regulates turnover of another core clock component, Period1, thus establishing the first functionally important circadian splicing switch in a mammalian system. Furthermore, recently generated U2AF26 deficient mice show altered adaptation of the clockwork in response to jetlag, confirming the relevance of U2AF26 for the circadian clock in vivo (Preussner et al., 2014, Mol Cell).
Based on this work, we have addressed the mechanistic basis for circadian alternative splicing. Using cell culture as well as in vivo models we have identified a large group of exons whose splicing pattern responds fast and extremely sensitive to temperature changes in the physiological temperature range. As many of these exons show rhythmic splicing in vivo, we suggest that this ‘splicing based thermometer’ uses circadian changes in body temperature as input to control a concerted splicing change in a group of exons in functionally related genes. We are now addressing the functionality of some of these temperature-sensitive splicing events and are investigating the molecular events that directly act as temperature sensor.
In addition, we are using a primary cell culture system to address the role of other (pre-)mRNA processing events in controlling rhythmic accumulation of circadian output genes.