6 research outputs found
BRP-170 and BRP190 isoforms of Bruchpilot protein differentially contribute to the frequency of synapses and synaptic circadian plasticity in the visual system of Drosophila
In the first optic neuropil (lamina) of the optic lobe of Drosophila
melanogaster, two classes of synapses, tetrad and feedback, show daily rhythms
in the number and size of presynaptic profiles examined at the level of
transmission electron microscopy (TEM). Number of tetrad presynaptic profiles
increases twice a day, once in the morning and again in the evening, and their
presynaptic ribbons are largest in the evening. In contrast, feedback synapses
peak at night. The frequency of synapses is correlated with size of the
presynaptic element measured as the platform size of so-called T-bars, with
T-bar platforms being largest with increasing synapse frequency. The large
scaffold protein Bruchpilot (BRP) is a major essential constituent of T-bars,
with two major isoforms of 190 and 170 kD forming T-bars of the peripheral
neuromuscular junctions (NMJ) synapses and in the brain. In addition to the
analysis of cyclic plasticity of tetrad and feedback synapses in wild-type
flies, we used TEM to examine daily changes in the size and distribution of
synapses within isoform-specific BRP mutants, expressing BRP-190 (BRPΔ170) or
BRP-170 (BRPΔ190) only. We found that the number and circadian plasticity of
synapses depends on both isoforms. In the BRPΔ190 lacking BRP-190 there was
almost 50% less tetrad synapses demonstrable than when both isoforms were
present. The lack of BRP-170 and BRP-190 increased and decreased, respectively
the number of feedback synapses, indicating that BRP-190 forms most of the
feedback synapses. In both mutants, the daily plasticity of tetrad and
feedback presynaptic profiles was abolished, except for feedback synapses in
BRPΔ190. The oscillations in the number and size of presynaptic elements seem
to depend on a different contribution of BRP isoforms in a presynaptic element
at different time during the day and night and at various synapse types. The
participation of both BRP isoforms may vary in different classes of synapses
External and circadian inputs modulate synaptic protein expression in the visual system of Drosophila melanogaster
In the visual system of Drosophila melanogaster the retina photoreceptors form tetrad synapses with the first order interneurons, amacrine cells and glial cells in the first optic neuropil (lamina), in order to transmit photic and visual information to the brain. Using the specific antibodies against synaptic proteins; Bruchpilot (BRP), Synapsin (SYN), and Disc Large (DLG), the synapses in the distal lamina were specifically labeled. Then their abundance was measured as immunofluorescence intensity in flies held in light/dark (LD 12:12), constant darkness (DD), and after locomotor and light stimulation. Moreover, the levels of proteins (SYN and DLG), and mRNAs of the brp, syn, and dlg genes, were measured in the fly's head and brain, respectively. In the head we did not detect SYN and DLG oscillations. We found, however, that in the lamina, DLG oscillates in LD 12:12 and DD but SYN cycles only in DD. The abundance of all synaptic proteins was also changed in the lamina after locomotor and light stimulation. One hour locomotor stimulations at different time points in LD 12:12 affected the pattern of the daily rhythm of synaptic proteins. In turn, light stimulations in DD increased the level of all proteins studied. In the case of SYN, however, this effect was observed only after a short light pulse (15 min). In contrast to proteins studied in the lamina, the mRNA of brp, syn, and dlg genes in the brain was not cycling in LD 12:12 and DD, except the mRNA of dlg in LD 12:12. Our earlier results and obtained in the present study showed that the abundance of BRP, SYN and DLG in the distal lamina, at the tetrad synapses, is regulated by light and a circadian clock while locomotor stimulation affects their daily pattern of expression. The observed changes in the level of synaptic markers reflect the circadian plasticity of tetrad synapses regulated by the circadian clock and external inputs, both specific and unspecific for the visual system