Hofbauer-Buchner Eyelet Affects Circadian Photosensitivity and Coordinates TIM and PER Expression in Drosophila Clock Neurons

Jan 19, 2007Journal of biological rhythms

Eyelet cells influence daily light sensitivity and coordinate clock protein levels in fruit fly timing neurons

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Abstract

Blocking synaptic transmission from the Hofbauer-Buchner eyelet impaired Drosophila melanogaster's ability to resynchronize behavior under jet-lag conditions.

The Hofbauer-Buchner eyelet is implicated as a circadian photoreceptor in fruit flies.
Impairing synaptic communication between the H-B eyelet and ventral circadian pacemaker neurons disrupts molecular and behavioral rhythm synchronization.
This disruption occurs even in the context of nonfunctional retinal photoreception and a mutation in the CRY gene.
Increased numbers of flies failed to synchronize to extreme photoperiods when synaptic transmission from the H-B eyelet was blocked.
Synchronized expression of clock proteins TIM and PER in clock neurons was also affected by the manipulation.

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Extraretinal photoreception is a common input route for light resetting signals into the circadian clock of animals. In Drosophila melanogaster, substantial circadian light inputs are mediated via the blue light photoreceptor CRYPTOCHROME (CRY) expressed in clock neurons within the brain. The current model predicts that, upon light activation, CRY interacts with the clock proteins TIMELESS (TIM) and PERIOD (PER), thereby inducing their degradation, which in turn leads to a resetting of the molecular oscillations within the circadian clock. Here the authors investigate the function of another putative extraretinal circadian photoreceptor, the Hofbauer-Buchner eyelet (H-B eyelet), located between the retina and the medulla in the fly optic lobes. Blocking synaptic transmission between the H-B eyelet and its potential target cells, the ventral circadian pacemaker neurons, impaired the flies' ability to resynchronize their behavior under jet-lag conditions in the context of nonfunctional retinal photoreception and a mutation in the CRY-encoding gene. The same manipulation also affected synchronized expression of the clock proteins TIM and PER in different subsets of the clock neurons. This shows that synaptic communication between the H-B eyelet and clock neurons contributes to synchronization of molecular and behavioral rhythms and confirms that the H-B eyelet functions as a circadian photoreceptor. Blockage of synaptic transmission from the H-B eyelet in the presence of functional compound eyes and the absence of CRY also results in increased numbers of flies that are unable to synchronize to extreme photoperiods, supplying independent proof for the role of the H-B eyelet as a circadian photoreceptor.

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Hofbauer-Buchner Eyelet Affects Circadian Photosensitivity and Coordinates TIM and PER Expression in Drosophila Clock Neurons

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