Brain connectivity inversely scales with developmental temperature in Drosophila

Abstract

Highlights d Developmental temperature affects synapse numbers and partner availability in flies d Development at 18 C results in synaptic partnerships absent at 25 C d The same non-canonical synapses form at 18 C and in the absence of a main partner at 25 C d Adult behavioral activity is adapted for the temperature at which the fly developed

A critical developmental interval of coupling axon branching to synaptic degradation during neural circuit formation

“…In contrast, loss of EGFR activity resulted in a significant decrease of BrpD3-GFP puncta – which colocalize with endogenous Brp (Fig.S3E,E’-F,F’) – in terminal branches from 0.22 puncta per µm to 0.1per µm. This corresponds to a 2.5-fold decrease in the total number of BrpD3 puncta from ∼15 per axon to ∼6.5 per axon and was accompanied by a redistribution from numerous small puncta at presynaptic sites into a few large BrpD3 aggregates (arrow) (Fig.3C,C’-D,D’,F,G), an indicator of loss of endogenous active zones in DCNs (Kiral et al ., 2021).…”

“…We have previously shown that the M-DCNs regulates behavioral responses in the multiparametric single fly visual response assay called Buridan’s paradigm (Linneweber et al ., 2020). In this assay, single flies walk freely between two identical visual cues (Fig.7A) and reduction of synapses causes increased fly activity when flies were tested at the same temperature at which they developed (Kiral et al ., 2021). Consistent with this, we find that inactivation of EGFR specifically in DCNs results in flies walking longer distances, staying active for a longer time, and increasing the number of walks between the two cues (Fig.7B-H; Table S1).…”

“…This corresponds to a 2.5-fold decrease in the total number of BrpD3 puncta from ~15 per axon to ~6.5 per axon and was accompanied by a redistribution from numerous small puncta at presynaptic sites into a few large BrpD3 aggregates (arrow) (Fig. 3C,C'-D,D',F,G), an indicator of loss of endogenous active zones in DCNs (Kiral et al, 2021).…”

“…Tissues were mounted on taped cover slides using vector shield. Images were obtained with a Leica TCS SP8-X white laser confocal microscope with a 63x glycerol objective (NA=1.3)(Jin et al ., 2018; Kiral et al ., 2021).…”

“…For activity-dependent GRASP experiments, to activate DCNs, freshly eclosed flies were transferred to 25°C incubator with 12-12hours light-dark cycle for 5 days. Brains were dissected and stained with a polyclonal anti-GFP antibody to label DCN pre-synaptic sites, monoclonal anti-GFP antibody to label GRASP signal, and polyclonal anti-CD4 antibody to label postsynaptic neurons(Kiral et al ., 2021).…”