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Fig. 1
Epidermal PIP2 accumulation marks sites of dendrite ensheathment.
( A) Schematic depicting epidermal neurite ensheathment in the Drosophila larval body wall. ( B, C) SBF-SEM analysis of epidermal dendrite ensheathment. ( B’ and B”) Traces of da neuron dendrites and epidermal sheaths in cross-section. ( C) Serial sections showing epidermal ensheathment (arrowheads mark sheaths) of da neuron dendrites (shaded green). The dendrite present in sections z1-z38 branches inside an epidermal sheath. See also Figure 1—video 1. ( D, E) Assay for markers of dendrite ensheathment. GFP-tagged markers were specifically expressed in the epidermis ( A58-Gal4, Cha-Gal80) in larvae expressing the c4da-specific marker ppk-CD4-tdTomato. Maximum intensity projections of membrane-targeted CD4-tdGFP ( D) and c4da dendrites ( E) are shown. Insets show magnified views of c4da dendrites (top) and c4da soma (bottom). ( F–K) Epidermal PLCδ-PH-GFP labels sites of dendrite ensheathment. Maximum intensity projections of epidermal PLCδ-PH-GFP ( F, H, J) and overlay showing PLCδ-PH-GFP signal in green and ppk-CD4-tdTomato in magenta to label c4da dendrites ( G, I, K). Hatched lines mark sheaths. ( F–I) XY projections of live confocal images. ( J, K) Representative image showing epithelial PIP2 distribution at sites of c4da dendrite contact visualized using expansion microscopy. Image shows a side view of a single epithelial cell and ensheathed c4da dendrites oriented along the apical-basal axis (apical, top). Note the discontinuities in the epithelial sheath at the dendrite branch point and at epithelial intracellular junctions (arrowheads). Sheaths from six independent neurons analyzed with expansion microscopy showed similar structures. Scale bars have been divided by the measured expansion factor of ~4 × and therefore refers to pre-expansion dimensions. ( L–U) Epidermal sheath markers. Maximum intensity projections show the distribution of the indicated GFP reporters in the epidermis of 120 h after egg laying (AEL) larvae and composites show portions of c4da dendrite arbors (shaded purple) wrapped by sheaths labeled by the GFP reporters.