Figure 1: Dendrite thinning correlates with Ca²⁺ transients initiation.

(a) Live confocal image and corresponding schematic trace of a C4da neuron labelled with mCD8-RFP before the initiation of Ca²⁺ transients (0.5 h a.p.f.). Dendritic branches corresponding future branch units are shown with colours. Three coloured rectangles in the left are the regions from which fluorescent traces of GCaMP6s in b were obtained. The coloured areas in the right trace (c1 to c3) correspond to the regions shown in c. Scale bar, 20 μm. (b) Time traces of GCaMP6s fluorescence in three different regions, the locations of which are indicated in a. Coloured arrows indicate the first Ca²⁺ transients in each branch unit. The coloured horizontal lines define the time window for c. (c) Time-lapse series of live confocal images of mCD8-RFP fluorescence. Magenta arrowheads indicate the proximal edges of branch units. Time stamps are minutes after the initiation of Ca²⁺ transients. The branch units are visualized with ratiometric images of GCaMP6s. Rectangles correspond to the regions for analyses in d. (d) Time traces of relative branch width in two regions. The corresponding regions are indicated in c with the same colours. (e) Time traces of relative branch width at the boundary of branch units and non-branch units. All the traces are time-aligned to the onset of Ca²⁺ transients. Six regions from four animals are analysed. (f) Quantification of branch width at the proximal dendrites of branch units and non-branch units. *P<0.05; Student’s t-test. Error bars, s.e. (g) Schematic diagram showing the temporal and spatial relationship between the proximal thinning and Ca²⁺ transients initiation.