Functional approaches to the dissection of a circadian system
Roenneberg, T., Eisensamer, B., Merrow, M.
Inst. f. Med. Psychol., Goethestr. 31, D-80336 München, Germany
The marine algae Gonyaulax polyedra is a traditional model organism for research of circadian rhythms. It has many circadian phenotypes which can be monitored automatically (or even simultaneously) for many weeks. The unicell Gonyaulax shows - like higher organisms - complex behaviour. Recently, our research has focused on biochemical pathways closely related to the circadian system. The best characterized of these is the
nitrogen assimilation pathway. Nitrate uptake, NR-activity, and other components of the pathway are under circadian control, as well as influenced by light. However, nitrate can also affect the Gonyaulax-clock as a non-photic zeitgeber. Thus, this pathway clearly represents both circadian input and circadian output. We have identified the nitrogen pathway up to the peroxisomes also involved in photorespiration. Inhibition of
one of the key peroxisomal enzymes (glycolate oxidase, GOX) has strong effects on the circadian system. All circadian nitrogen effects appear to focus on glycine which is an important precursor for both purine and porphyrin synthesis. Photosynthesis can be measured indirectly by monitoring the pH of the culture medium which oscillates in a circadian fashion under constant conditions. Like in the case of nitrate, pH changes themselves can also reset the clock and form yet another metabolic feed-back within the circadian system. This functional approach provides a basis for molecular studies. We are currently isolating enzymes within the identified pathway with the aim of cloning their genes. These enzymes are part of the clock's input as well as being under circadian control, and their regulation is thus, important both for circadian in- and output.
| LOCATION |
DATE |
TIME |
| Lecture Hall II |
Thursday, April 9 |
02:40 pm |