(A–J) Characterization of the cell cycle phasing of cells in Tr2 DT at different larval stages. (A,C,E,G,I) Phospho-Histone H3 immunostaining at different larval stages indicated (pH3, red, arrowheads; DAPI, blue). (B,D,F,H,J) BrdU immunostaining at different larval stages indicated (BrdU, white arrowheads; DAPI, blue). Scale bar = 50 µm. (K–L) Expression of FUCCI reporters E2F1-GFP (green, arrowheads) and CyclinB-RFP (red) in Tr2 DT in early L1. (M) Mitotic indices of Tr2 DT in wild type larvae at different larval stages. Graph shows the frequency of pH3+ nuclei in Tr2 DT at indicated stages (mean ± standard deviation, n = 6 tracheae per timepoint). Scale bar = 10 µm.