A robust and self-sustained peripheral circadian oscillator reveals differences in temperature compensation properties with central brain clocks

Abstract

Circadian clocks temporally organize physiology and behavior of organisms exposed to the daily changes of light and temperature on our planet, thereby contributing to fitness and health. Circadian clocks and the biological rhythms they control are characterized by three properties. (1) The rhythms are self-sustained in constant conditions with a period of ~ 24 hr,(2), they can be synchronized to the environmental cycles of light and temperature, and (3), they are temperature compensated, meaning they run with the same speed at different temperatures within the physiological range of the organism. Apart from the central clocks located in or near the brain, which regulate the daily activity rhythms of animals, the so-called peripheral clocks are dispersed throughout the body of insects and vertebrates. Based on the three defining properties, it has been difficult to determine if these peripheral clocks are true circadian clocks. We used a set of clock gene -luciferase reporter genes to address this question in Drosophila circadian clocks. We show that self-sustained fly peripheral oscillators over compensate temperature changes, i.e., they slow down with increasing temperature.This over-compensation is not observed in central clock neurons in the fly brain, both in intact flies and in cultured brains, suggesting that neural network properties contribute to temperature compensation. However, an important neuropeptide for synchronizing the circadian neuronal network, the Pigment Dispersing Factor (PDF), is not required for selfsustained and temperature-compensated oscillations in subsets of the central clock neurons.Our findings reveal a fundamental difference between central and peripheral clocks, which likely also applies for vertebrate clocks.

Nuclear Export of Drosophila PERIOD contributes to temperature compensation of the circadian clock

“…Next we analyzed the expression of a tim-luciferase (ptim-TIM-LUC) reporter gene that accurately reflects temporal TIM expression in peripheral clock cells (29,36). In a wild type background, ptim-TIM-LUC oscillations were indistinguishable at 18°C and 25°C, while oscillations were reduced in amplitude at 29°C (Figure S4A), similar to what we observed for BG-luc (Figure 4A).…”

“…Although it can be argued that signals were recorded from specific neuronal subsets, these subsets within the context of the entire network, which could of course influence the oscillations within one group. Nevertheless, even in the background of a Pdf 01 mutation, which largely prevents network coupling due to the lack of the PDF neuropeptide (17), temperature compensated clock gene expression was observed in dorsal subsets of the clock neurons (29). However, the same study revealed that circadian clocks in isolated fly tissues (in halteres and antennae) are over compensated, pointing to differences between neuronal and non-neuronal circadian clocks (29).…”

“…Nevertheless, even in the background of a Pdf 01 mutation, which largely prevents network coupling due to the lack of the PDF neuropeptide (17), temperature compensated clock gene expression was observed in dorsal subsets of the clock neurons (29). However, the same study revealed that circadian clocks in isolated fly tissues (in halteres and antennae) are over compensated, pointing to differences between neuronal and non-neuronal circadian clocks (29). Taken together, the currently available data support a model of cell autonomous temperature compensation, at least in central circadian clock neurons.…”

“…mean difference) and its precision (57). Data were analyzed using DABEST (57), using the website available under https://www.estimationstats.com/#/ as described (29).…”

The opposing Chloride Cotransporters KCC and NKCC control locomotor activity in constant light and during long days

“…The experiments were repeated three times and the total average is shown in Figure 4. For the statistical analysis of the data, estimation statistics was used 47 . Data were analyzed using DABEST 48 , using the website available under https://www.estimationstats.com/#/.…”