Role of Glycogen Synthase Kinase (GSK) in temperature compensation of the Neurospora circadian clock [Elektronische Ressource] / presented by Ozgur Tataroglu

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• Biologie

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2011
• Nombre de lectures: 23
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

DISSERTATION

submitted to the
combined faculties for the Natural Sciences and Mathematics
of the Ruperto-Carola University of Heidelberg, Germany
for the degree of
Doctor of Natural Sciences

Role of Glycogen Synthase Kinase (GSK) in
temperature compensation of the Neurospora
circadian clock
presented by



Master of Science: Ozgur Tataroglu
born in: Izmir/Turkei
Referees: Prof. Dr. M. Brunner
Prof. Dr. W. Nickel

Date of oral examination: 8 Feb 2011
1 DISSERTATION

zur
Erlangung der Doktorwürde
der
Naturwissenschaftlich-Mathematischen Gesamtfakultät der
Ruprecht-Karls-Universität Heidelberg


Rolle der Glykogen Synthase Kinase (GSK) in
der Temperaturkompensation der circadianen
Uhr von Neurospora crassa
vorgelegt von



Master of Science: Ozgur Tataroglu
Geburtsort: Izmir/Turkei
Gutachter: Prof. Dr. M. Brunner
Prof. Dr. W. Nickel

Tag der mündlichen Prüfung: 8 Feb 2011
2 ACKNOWLEDGEMENTS

ACKNOWLEDGEMENTS





I would like to thank Basak for everything and dedicate this work to her..


I also thank the members of the Brunner lab, in particular to Linda and Erik who
helped me so much. Without their help, I couldn’t have finished this work.

I also thank Michael, Axel and Tobias for their supervision and support.









3 TABLE OF CONTENTS

TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................................ 3  
TABLE OF CONTENTS .. 4  
SUMMARY ....................................................................................................................... 6  
ZUSAMMENFASSUNG ................................... 7  
1.   INTRODUCTION ...................................................................... 8  
1.1   Circadian clocks .......................................... 8  
1.1.1   Clocks in nature ................................................................... 8  
1.1.2   Organization of circadian hierarchy ..................................... 9  
1.2   Molecular mechanism of circadian clocks ................................ 10  
1.2.1   The transcription-translation feedback loop (TTFL) ......................................... 10  
1.2.2   Mammalian TTFL .............................................................................................. 12  
1.2.3   Drosophila TTFL ............................... 13  
1.2.4   A model organism for over half a century: Neurospora crassa .......................... 15  
1.2.5   Neurospora TTFL .............................................................................................. 16  
1.3   Temperature compensation of circadian clocks ........................ 19  
1.3.1   Fundamental, but poorly understood ................................................................. 19  
1.3.2   Mechanism of temperature compensation: Post-translational? .......................... 20  
1.3.3   Glycogen synthase kinase (GSK) and temperature compensation .................... 22  
2.   MATERIALS AND METHODS ............................................................................... 27  
2.1   Neurospora strains ..................................... 27  
2.2   Neurospora growth conditions .................. 27  
2.3   Preparation of total cell lysates from Neurospora ..................................................... 27  
2.4   Sub-cellular fractionation of frozen mycelia ............................. 29  
2.5   Protein determination and analysis ............................................................................ 29  
2.6   Generation of HIS-tagged CKI and GSK plasmids ................... 29  
4 TABLE OF CONTENTS

2.7   Expression and purification of active kinases from E.coli ........................................ 32  
2.8   In vitro phosphorylation in Neurospora total cell extracts ........ 33  
2.9   Co-immunoprecipitation in Neurospora total cell lysates ........................................ 33  
2.10   Quantitative real-time PCR .................................................... 34  
2.11   Generation of pWC1-WC1 plasmids and strains ................................................... 35  
3.   RESULTS ............................................................................... 40  
3.1   Down-regulation of GSK results in loss of temperature compensation .................... 40  
3.2   Down-regulation of GSK increases WC-1 levels ...................................................... 43  
3.3   GSK binds to WCC in vivo ....................................................... 47  
3.4   GSK phosphorylates WCC, but not FRQ .................................................................. 51  
3.5   GSK phosphorylates a specific region on WC-1 ....................... 54  
3.6   Mutations of WC1 result in loss of temperature compensation ................................ 57  
3.7   Mutations of WC1 lead to higher levels of WC-1 ..................................................... 60  
4.   DISCUSSION .......................................................................... 65  
4.1   GSK affects temperature compensation through stabilizing the WCC ..................... 65  
4.2   Recruitment of GSK to WCC modulates a phospho-degron on WC-1 69  
4.3   Mutation of the phosphodegron shortens the period by stabilizing WC-1 ................ 72  
4.4   Opposing functions of GSK and CK2 regulate temperature compensation in
Neurospora crassa ............................................................................................................... 75  
5.   REFERENCES ....... 78  
6.   NOTES FOR THE READER ................................................................................... 86  

5 SUMMARY


SUMMARY

Circadian clocks are biological oscillators that allow organisms to accurately
predict and adjust to the rhythmic changes in the environment which increases
their fitness. These oscillators are found in every cell and have three fundamental
properties: they are endogenous, entrainable and temperature compensated. The
former two properties of the clock are well studied. However, it is currently
unknown how clocks accurately keep the time independent of the ambient
temperature, a phenomenon known as “temperature compensation”. This is
particularly important for poikilothermic organisms that cannot control their body
temperature and yet still have accurate circadian clocks.
We used Neurospora crassa as a eukaryotic circadian clock model organism and
showed that Glycogen synthase kinase (GSK) binds and specifically
phosphorylates White Collar 1 (WC-1), which is the critical and rate-limiting
positive element of the Neurospora clock. We found that these phosphorylations
decrease the WC-1 stability in a temperature dependent manner. Our data
completes the picture in our current understanding of temperature compensation
of circadian clocks and shows that temperature compensation in Neurospora
crassa is achieved by opposing functions of two kinases (GSK and CK2) on the
positive (WCC) and negative (FRQ) elements of the clock, respectively. Since
both kinases are well conserved among eukaryotes, it is also possible that this
mechanism of temperature compensation is conserved among other eukaryotic
circadian clocks.
6 SUMMARY



ZUSAMMENFASSUNG
Circadiane Uhren sind biologische Oszillatoren, die es Organismen ermöglichen,
rhythmische Änderungen in der Umwelt vorherzusagen und sich auf diese
einzustellen. Diese Oszillatoren haben drei fundamentale Eigenschaften: sie sind
endogen, trainierbar und temperaturkompensiert. Die ersten beiden
Eigenschaften der Uhr wurden bereits eingehend studiert. Bis heute ist jedoch
nicht bekannt, wie die zellulären Uhren unabhängig von der
Umgebungstemperatur akkurat Zeit messen können, ein Phänomen, das als
Temperaturkompensation bezeichnet wird. Vor allem für poikilotherme
Lebewesen, die ihre Körpertemperatur nicht selbst regulieren können, ist diese
Eigenschaft sehr wichtig.

Im eukaryontischen Modellorganismus, Neurospora crassa, haben wir gezeigt,
dass Glykogen Synthase Kinase (GSK) den Transkriptionsfaktor White Collar 1
(WC-1) bindet, spezifisch phosphoryliert und damit temperaturabhängig dessen
Stabilität reguliert. WC-1 ist das limitierende, positive Element in der Neurospora
Uhr und bildet mit WC-2 den White Collar Complex (WCC). Bei erhöhten
Temperaturen wird WC-1 durch GSK-vermittelte Phosphorylierung destabilisiert.
Die vorliegenden Daten vervollständigen das Bild dessen, wie wir uns
gegenwärtig das Prinzip der Temperaturkompensation circadianer U