Abstract
A major challenge for all organisms that live in temperate and subpolar regions is to adapt physiology and activity to different photoperiods. A long-standing model assumes that there are morning (M) and evening (E) oscillators with different photoreceptive properties that couple to dawn and dusk, respectively, and by this way adjust activity to the different photoperiods. In the fruit fly Drosophila melanogaster, M and E oscillators have been localized to specific circadian clock neurons in the brain. Here, we investigate under different photoperiods the activity pattern of flies expressing the clock protein PERIOD (PER) only in subsets of M and E oscillators. We found that all fly lines that expressed PER only in subsets of the clock neurons had difficulties to track the morning and evening in a wild-type manner. The lack of the E oscillators advanced M activity under short days, whereas the lack of the M oscillators delayed E activity under the same conditions. In addition, we found that flies expressing PER only in subsets of clock neurons showed higher activity levels at certain times of day or night, suggesting that M and E clock neurons might inhibit activity at specific moments throughout the 24 h. Altogether, we show that the proper interaction between all clock cells is important for adapting the flies’ activity to different photoperiods and discuss our findings in the light of the current literature.
Highlights
Endogenous clocks that tick with an ∼24 h period control circadian rhythms
In flies expressing PER only in M-LN, E-LN, and M-DN (Figure 5B, 2nd column), the nocturnal activity is strongly suppressed, suggesting an inhibitory effect of the E-LN. These findings indicate that some clock neurons inhibit nocturnal activity at certain times during the night while others promote it at other times of the night
Since the discovery that specific clock neurons control M and E activity of D. melanogaster, many studies tested the properties of M and E oscillators in detail
Summary
Endogenous clocks that tick with an ∼24 h period control circadian rhythms. They entrain to the 24 h cycles of the earth via external Zeitgebers, the strongest of which is light. Morning and Evening Neurons in Entrainment by being active mainly in the morning and evening Such an adaptation is especially important for small insects such as fruit flies that are in danger of desiccation (Hamblen-Coyle et al, 1992; Majercak et al, 1999; Bywalez et al, 2012). This behavior occurs in the laboratory under light–dark (LD) cycles but constant temperatures showing that light is the major cue that drives these changes (Rieger et al, 2003, 2007, 2012; Shafer et al, 2004; Menegazzi et al, 2017; Schlichting et al, 2019b)
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