Circadian rhythms in the morphology of neurons in Drosophila

Abstract

Neurons have an enormous capacity to adapt to changing conditions through the regulation of gene expression, morphology, and physiology. In the fruit fly Drosophila melanogaster, this plasticity includes recurrent changes taking place within intervals of a few hours during the day. The rhythmic alterations in the morphology of neurons described so far include changes in axonal diameter, branching complexity, synapse numbers, and the number of synaptic vesicles. The cycles of these changes have larger amplitude when the fly is exposed to light, but they persist in constant darkness and require the expression of the clock genes period and timeless, leading to the concept of circadian plasticity. The molecular mechanisms driving these cycles appear to require the expression of these genes either inside the neurons themselves or in other peripheral pacemaker cells. Loss-of-function mutations in period and timeless not only abolish the morphological rhythms, but also often cause abnormal axonal branching suggesting that circadian plasticity is relevant for the maintenance of normal morphology. Research into whether (1) circadian plasticity is a common feature of neurons in all animals and (2) our own neurons change shape between day and night will be of interest.

Glia-related circadian plasticity in the visual system of Diptera

“…To maintain synchrony with environmental cycles, this rhythmicity is entrained by an external cycle of day and night (LD), but it is generated predominantly by the endogenous pacemakers, the circadian clocks, that produce oscillations with a period of approximately 24 h. Due to timing signals from the clocks, the phenomenon of rhythmic changes persists also in the condition of constant darkness (DD), representing an example of a particular type of plasticity, the circadian plasticity (Frenkel and Ceriani, 2011; Mehnert and Cantera, 2011). …”

Circadian Rhythm Neuropeptides in Drosophila: Signals for Normal Circadian Function and Circadian Neurodegenerative Disease

“…While the activation was only detected in circadian mutants of young flies, caspase activation was also detected in older wild-type flies, suggesting that circadian dysfunction arises in older flies mimicking that produced by mutations in younger flies [109]. Moreover, there is an extensive literature showing daily PDF-dependent changes in neuronal cell size and synaptic architecture in the optic lobes (reviewed in [113]). Since caspases have been implicated in synaptic pruning processes [114], it is possible that circadian dysfunction contributes to hyperactivation of this synaptic pruning pathway in circadian mutants or older wild-type flies.…”

Synchrony and desynchrony in circadian clocks: impacts on learning and memory

“…Circadian changes in synapse number have been observed at Drosophila neuromuscular junctions along with circadian changes in motor neuron morphology (Mehnert and Cantera 2011;Ruiz et al 2013). Dendrite length also is circadianly regulated in the optic lobe with larger dendritic trees observed early in the (subjective) day (Weber et al 2009;Damulewicz and Pyza 2011).…”