Circadian expression of the presynaptic active zone protein bruchpilot in the lamina of Drosophila melanogaster

Abstract

In the fly's visual system, the morphology of cells and the number of synapses change during the day. In the present study we show that in the first optic neuropil (lamina) of Drosophila melanogaster, a presynaptic active zone protein Bruchpilot (BRP) exhibits a circadian rhythm in abundance. In day/night (or light/dark, LD) conditions the level of BRP increases two times, in the morning and in the evening. The same pattern of changes in the BRP level was detected in whole brain homogenates, thus indicating that the majority of synapses in the brain peaks twice during the day. However, these two peaks in BRP abundance, measured as the fluorescence intensity of immunolabeling, seem to be regulated differently. The peak in the morning is predominantly regulated by light and involves the transduction pathway in the retina photoreceptors. This peak is present neither in wild-type Canton-S flies in constant darkness (DD), nor in norpA(7) phototransduction mutant in LD. However, it also depends on the clock gene per, because it is abolished in the per(0) arrhythmic mutant. In turn, the peak of BRP in the evening is endogenously regulated by an input from the pacemaker located in the brain. This peak is present in Canton-S flies in DD, as well as in the norpA(7) mutant in LD, but is absent in per(01), tim,(01) and cry(01) mutants in LD. In addition both peaks seem to depend on clock gene-expressing photoreceptors and glial cells of the visual system.

Cryptochrome Is a Regulator of Synaptic Plasticity in the Visual System of Drosophila melanogaster

“…Some of those were around 65 kDa in size, which is the molecular weight predicted for CRY. Prompted by this observation and by previous work showing a genetic interaction between cry and brp (Górska-Andrzejak et al, 2013) we explored whether a physical interaction occurs between the two proteins. We precipitated BRP with the nc82 antibody, which targets the C-terminus of the protein hence both the 170 kDa and the 190 kDa isoforms (Matkovic et al, 2013).…”

“…Within cartridges many synaptic contacts are formed between cells, including tetrad synapses between the photoreceptor terminals R1–R6 and four postsynaptic partners among the following cell types: L1, L2, β-processes of amacrine cells, glial cells or L3 (Prokop and Meinertzhagen, 2006). In the distal lamina BRP expression is rhythmic, showing a light-dependent peak at the beginning of the day (ZT1) and a clock dependent peak at the beginning of the night (ZT13, Górska-Andrzejak et al, 2013 and Figures 3A,D,G,H). The cry 01 mutation changes this pattern as BRP levels are high across the whole day and only decrease in the middle of the night (ZT16, Górska-Andrzejak et al, 2013 and Figures 3B,E).…”

“…In line with this findings, CRY accumulates in the projections of neurons where it is expressed (Klarsfeld et al, 2004), it binds to components of the phototransduction pathway in the retinal photoreceptors (Mazzotta et al, 2013) and is involved in magnetoreception (Gegear et al, 2008; Ritz et al, 2010; Fedele et al, 2014a,b; Bazalova et al, 2016). Moreover, CRY has an essential role in circadian plasticity in the lamina: in fact, in cry -null ( cry 0 ) mutants the cyclic expression of genes regulating circadian changes in morphology of neurons and synapses is altered (Górska-Andrzejak et al, 2013; Damulewicz et al, 2015). …”

“…In our previous work we looked at the rhythmic plasticity of the synapses in the visual system by examining the expression of BRUCHPILOT (BRP) under light/dark (LD 12:12) and constant dark (DD) conditions (Górska-Andrzejak et al, 2013). Using mutants we revealed that the expression of BRP in the distal lamina is under control of both the circadian clock and the light-dark cycle, and that CRY possibly exerts an additional control.…”

Circadian Pacemaker Neurons Change Synaptic Contacts across the Day

“…Circadian changes in the abundance of the presynaptic active zone BRP have also been shown in the first optic neuropil of the fly brain, although BRP abundance in the lamina increases in the early night under DD conditions [20], in contrast to the oscillations in BRP levels observed at the dorsal protocerebrum that peak in the early subjective day just described. In addition, rhythmic changes in the number of synapses have also been described in the terminals of adult motor neurons in Drosophila [21] examined through transmission electron microscopy as well as BRP + light confocal microscopy, underscoring the validity of the approach employed herein.…”