CRY-dependent plasticity of tetrad presynaptic sites in the visual system of Drosophila at the morning peak of activity and sleep

Abstract

Tetrad synapses are formed between the retina photoreceptor terminals and postsynaptic cells in the first optic neuropil (lamina) of Drosophila. They are remodelled in the course of the day and show distinct functional changes during activity and sleep. These changes result from fast degradation of the presynaptic scaffolding protein Bruchpilot (BRP) by Cryptochrome (CRY) in the morning and depend on BRP-170, one of two BRP isoforms. This process also affects the number of synaptic vesicles, both clear and dense-core, delivered to the presynaptic elements. In cry01 mutants lacking CRY and in brpΔ170, the number of synaptic vesicles is lower in the morning peak of activity than during night-sleep while in wild-type flies the number of synaptic vesicles is similar at these two time points. CRY may also set phase of the circadian rhythm in plasticity of synapses. The process of synapse remodelling stimulates the formation of clear synaptic vesicles in the morning. They carry histamine, a neurotransmitter in tetrad synapses and seem to be formed from glial capitate projections inside the photoreceptor terminals. In turn dense-core vesicles probably carry synaptic proteins building the tetrad presynaptic element.

The neuropeptide pigment‐dispersing factor signals independently of Bruchpilot‐labelled active zones in daily remodelled terminals of Drosophila clock neurons

“…In addition, the cell bodies were strongly labelled by BRP GFP . Larger dense vesicles close to BRP‐containing tetrad presynaptic sites in the visual system are reported for Drosophila and have been suggested to carry presynaptic proteins to the active zone (Damulewicz et al, 2020). Similarly, the luminal BRP GFP in our preparations may label transport vesicles that deliver BRP to active zones.…”

Integration of Circadian Clock Information in the Drosophila Circadian Neuronal Network

“…The l-LNvs are the target neuronal clusters within the CNN for many arousal promoting neurotransmitters ( Mazzotta et al, 2020 ). The HB-eyelet, a light-sensing body in the retina, and photoreceptors from the eye form synaptic connections with the LNvs, which contributes to morning arousal ( Damulewicz et al, 2020 ; Helfrich-Förster et al, 2002 ; Hofbauer and Buchner, 1989 ; Veleri et al, 2007 ). Light information is communicated to the LNvs through excitatory cholinergic and inhibitory histaminergic signals, though how these two neurotransmitters are coordinated is unclear ( Schlichting et al, 2016 ).…”

“…Here, the authors ablate dorsal medial termini of the s-LNvs and find no effect on behavioral rhythms in DD. Underscoring the link between light and synaptic plasticity, CRY has recently been implicated in circadian rhythmicity in synaptic plasticity ( Damulewicz et al, 2020 ). Another recent report using CRISPR ablation of circadian clocks also undermines a central role for s-LNvs ( Delventhal et al, 2019 ).…”

Roles of peripheral clocks: lessons from the fly

“…In the absence of CRY, BRP levels remain constantly high in the distal lamina during the light phase, whereas overexpression of a constitutively active form of CRY decreases laminal BRP levels throughout the whole day [268]. By regulating the stability of BRP, CRY might set the phase of circadian plasticity in the tetrad synapses of lamina [269].…”