CIRCADIAN RHYTHMS Understanding how biological clocks control
daily rhythms Dr. Brigitte Dauwalder Associate Professor Department
of Biology and Biochemistry University of Houston
[email protected]
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Rhythm (Circa Diem = Approximately a Day)
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Geophysical cycles are the basis of daily biological rhythms
The earth rotates on its axis once every 24 hours Daily cycles of
-Light -Temperature -Humidity Very predictable changes Organisms
have evolved to coordinate their activities with the day-night
cycle
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Jean Jacques de Mairan (1729)
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Circadian clocks anticipate environmental changes
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Circadian clocks controlling social behaviour Guy Bloch, Dan P.
Toma and Gene E. Robinson
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Annual geophysical cycles are the basis of seasonal rhythms The
earth is tilted on its axis and revolves around the sun Seasonal
changes correlate with changes in the ratio of light and dark each
day Changes are very predictable
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The monarch long-distance migration From Reppert et al, TINS
2010 Fall Oriented flight south Increased life span Reproductive
diapause Roosts College station
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Circadian rhythms continue in a constant environmentbiological
clocks! Circadian clocks synchronize physiology, metabolism and
behavior to the external environment, thereby enabling anticipation
of daily environmental changes
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Circadian rhythms are relatively insensitive to changes in
temperature: They are temperature compensated In biochemical
reactions, Q 10 = 2-3 For circadian rhythms, Q 10 = 0.8-1.3 Q 10 =
frequency at Temp 1 frequency at Temp 1 - 10 o C
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Circadian Clock Properties Entrained by environmental cues
Light Temperature Food Social cues Rhythms persist in constant
conditions periods close to 24 h. (circa-dian) Temperature
compensated Can be used to tell time Sun compass orientation
Seasonal breeding
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Individual tissues have clocks too
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How do circadian clocks keep time and control rhythms? Model
Systems!
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Measuring Locomotor Activity in Drosophila Days 1 10 5 Time of
Day (h) 0 24 48 LD DD LD = Light/Dark Cycle DD = Constant
Darkness
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per 01 Konopka and Benzer, PNAS, 1971 The period mutants of
Drosophila PAS 1 1218 A B per L per S TG
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per mRNA and protein abundance cycle in a circadian manner
Relative abundance Zeitgeber Time PER protein per mRNA
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Per and tim genes Tim protein NUCLEUSCYTOPLASM Per protein Per
mRNATim mRNA
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Per and tim genes Tim protein Tim Protein active
NUCLEUSCYTOPLASM Per mRNATim mRNA
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Clock and cyc genes Clock protein Cyc protein Per and tim genes
Tim protein Tim Protein active NUCLEUSCYTOPLASM Per mRNATim
mRNA
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Clock and cyc genes Clock protein Cyc protein Per and tim genes
Tim protein Tim Protein active NUCLEUSCYTOPLASM Per mRNATim
mRNA
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Clock and cyc genes Clock protein Cyc protein Per and tim genes
Tim protein Tim Protein active NUCLEUSCYTOPLASM Per mRNATim mRNA
FEEDBACK LOOP
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How do circadian clocks impact human health?
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Smolensky and Lamberg, The Body Clock Guide to Better Health.,
2000 Circadian rhythms in humans
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Hatori et al. (2012) Cell Metab. Circadian clocks, feeding and
obesity
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Sleep time and social jetlag
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Mammalian SCN
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Maywood et al., Current Biology 2006 mPer1::Luc Oscillations in
the SCN
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Circadian rhythms also regulate our sleep patterns
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The New York Times Goodnight. Sleep Clean.
http://www.nytimes.com/2014/01/12/opinion/sunday/goodnight-sleep-clean.html?emc=eta1&_r=0
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THE CIRCADIAN CIRCUITRY Clock mechanisms are highly conserved
between flies and mammals. In both mammals and flies, defined
groups of genes and neurons controls circadian behavior. These
neurons communicate to remain synchronized. Work in flies has
influenced mammalian studies, and vice versa, with regard to
thinking about circuit interactions in the circadian system (e.g.,
roles for neuropeptides). Much more needs to be discovered to
really understand the circadian clock and how it influences our
health !