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Chronobiologie (Subject) / Chronobiologie (Lesson)
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- 1) Which geophysical rhythms on earth do you know? Name one biological example for adaptation for each geophysical rhythm. - Circatidal rhythms - Fiddler crabs are active during low tide- Circadian rhythms - Melanopsin concentration in humans (high during night, low during day)- Circasemilunar rhythms - Clunio marinus has a semilunar rhythm in eclosion and in copulation- Circalunar rhythms - Povilla adusta flies eclose in high number from the pupal case 2 days after full moon- Circaannual rhythms - Reproduction, migration, hibernation; Mallards change their feather coat
- 2) Name several annual rhythms of plants and animals. Do annual rhythms indeed relay on an endogenous clock? Was this shown experimentally? Which parameters can be used by annunal clocks for synchronization to the annual seasons? Plants - Flowering, seed germination, growth, fall of leaves, frost resistance Animals - Reproduction, development (body weight, fur or feather change), over wintering or migration Yes, they rely on an endogenous clock and it was shown in an experiment where they monitored seed germination of the bean plant Phaseolus vulgaris in constant darkness, constant humidity and constant temperature and weighed them every month for three years; some were submersed in water for several hours and then weighed again - increase weight due to water uptake - water uptake was highest when beans were ready to germinate Parameters for annual clock synchronization - temperature and rainfall, food abundance, day length/photoperiod
- 4) List the most important properties of endogenous clocks. - Under constant conditions they free-run with a period (τ) of circa 24 hours (= circadian) - τ is species specific and genetically determined - τ is independent of the environmental temperature (= temperature compensated) - The endogenous clock can be synchronized by Zeitgebers („entrained“) (e.g. by light-dark cycles) - The endogenous clock can be resynchronized by shifted Zeitgebers, but it needs several days for doing so
- 6) What is the biological sense of daily rhythms? Give four reasons why internal clocks have advantages. - Organisms are prepared in advance for the cyclical changes in the environment - The endogenous clock enables time measurement - The endogenous clock provides a reference value for sun-compass orientation - The endogenous clock provides a reference value for measuring daylength - The different periods cause different phases of the rhythm in respect of the Zeitgeber (may have ecological advantages, or be advantageous for the group in social animals) - In multicellulars, the endogenous clock can synchronize (or adjust) all rhythms in the body
- 7) When did biological clocks evolve? Did they evolve only once? - They evolved early - They evolved several times independently, because the clock genes are conserved between cyanobacteria, plant, fungi and animals
- 8) What is the difference between parametric and non-parametric effects of light on endogenous clocks? - effects of constant light (daylight) on the endogenous clock = “tonic”, “parametric” o continuous (tonic) acceleration or deceleration of the clock - effects of short light (twilight) on the endogenous clock = “phasic”, “non-parametric” o Non-parametric effects of light: short-term acceleration (= advance) or deceleration (= delay) of the clock > Parametric: changing τ; Non-parametric: changing phase
- 9) Under which circumstances an arrhythmic life-style can be of advantage. When food, mating and things like that aren’t available around a certain time, but instead could be happening at any time of the day
- 10) Which are the main differences of the molecular clock components between flies and mice? Flies MiceCLK oscillates BMAL1 (CYC) oscillatesCLK activates per, tim transcription BMAL1 activates per, cry transcriptionTIM interacts with PER TIM is absentCRY acts as light receptor CRY interacts with PER and is unresponsive to lightTIM is degraded upon light Light leads to per transcription
- 11) What is the main function of the posttranscriptional feedback loops (PTFLs) in the molecular circadian clock? Can they alone be sufficient for rhythm generation? - The PTFLs modify the state of the clock proteins (e.g. their phosphorylation) and by this way influence their activity and induce a delay in the TTFLs (that is necessary for the circadian period) - The PTFLs alone may be sufficient to provoke circadian rhythms
- 12) Are circadian clocks essential for survival? Are they of selective evolutionary advantage? What is the evidence for the latter? - Endogenous clocks are not essential for survival, but they have a clear selective advantage - Reproductive fitness is reduced in arrhythmic flies à arrhythmic males produce less sperm - Clockless chipmunks leave the burrow more often at night and have a higher predation risk
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- 13) Please explain in detail two possibilities to determine the chronotype of a person. - Measure activity onset - Length of PER3 gene à long = early riser; short = late riser - Peripheral clock in fibroblasts can be used to determine the chronotype
- 15) Where in the brain of mammals and insects are the master circadian clocks located? How was this shown for hamsters and cockroaches? Do both clocks show similar characteristics? - Mammals - SCN; at the base of the third ventricle, just above the optic chiasm - Insects - optic lobes; accessory medulla - Cockroaches - transplantation and exchange of the optic lobes of two cockroaches with different LD cycles - Hamsters - transplantation and exchange of a fetal SCN of a Tau-mutant hamster and a wildtype hamster - Similarities o Close to the optic system o express homologous clock genes o utilize neuropeptides o close relation to the hormonal system
- 16) Describe the path of light from the eye to the mammalian SCN. Optic nerve > retinohypothalamic tract > SCN
- 18) How does the clock in the brain control the rhythms in the body of mammals? Describe briefly the different pathways. - It controls the body indirectly via the SCN - Photoperiod > Retina > SCN >via vasopressin> Paraventricular nuclei (PVN) >via CRH> Pituitary >ACTH> Adrenal glands > Plasma glucocorticoids (negative feedback on Pituitary and PVN) > regulates circadian clock - SCN >via dorsal and ventral subperiventricular zone (d-/vSPZ)> dorsomedial nucleus of the hypothalamus (DMH) > Orexin neurons (LH) - regulates waking, eating > PVN - regulates Melatonin - regulates prolactin with thyreotropin hormone (TH) and luteinizing hormone (LH) - regulates growth hormone - regulates stress (HPA) axis >via GABA> Ventrolateral preoptic area (VLPO) - regulates sleep - SCN > dorsal and ventral subperiventricular zone > Medial preoptic area - thermoregulation
- 19) What is temporal niche switching? What do you know about the underlying mechanisms? - In the context of chronobiology and endogenous clocks a temporal niche switch is organisms changing the time during which they’re active, like going from being nocturnal to being diurnal -
- 20) How autonomous are the peripheral clocks in the body of mammals? Can they entrain to Zeitgebers, independently of the SCN? - There can be central clock driven slave clocks, which are entirely driven by the central clock (Oenocytes), fully autonomous clocks, which are entirely driven by external Zeitgebers (Malphigian tubles) and slave autonomous clock, which are entrained by Zeitgebers and central clock (Prothoracic gland) - Liver of mice can be entrained by feeding; In “transparent” organisms like plants, zebrafishes and fruit flies the peripheral clocks can be entrained directly via light
- 21) Please explain the external and internal coincidence model of photoperiodic control. - Discovered by Pittendrigh and Minnis, 1964 - Two types of information need to be integrated by the plant for flowering to happen at a certain time o External information (light) o Internal information (provided by the circadian clock à molecular signal provided at a specific time of the day by the clock) - For flowering to happen, both signals need to happen at the same time (coincide)