DIAP1 dynamics in the SOP lineage. (A) External sensory organ. Sensory organs are formed by two external cells, the shaft (sf) and the socket (so) cells, and two inner cells, the internal neuron (n) and the sheath (sh) cell. (B) The SOP lineage. The progenitor cells, pI, pIIa, pIIb, and pIIIb (white) divide to form the five cells of the external sensory organ shown in A. The socket and shaft cells arise from the pIIa cell. The neuron, sheath, and glial (g) cells arise from the pIIb lineage. The glial cell soon dies by apoptosis. (C–L) PRAP protein dynamics in the SOP lineage at progressive stages of development. In vivo live-imaging analysis of PRAP (green) was begun at ∼16 h APF. The time course of the imaging analysis is shown at the bottom right of the merged panel. Glial cell death is indicated by white arrowheads. Note that in the shaft cell (yellow arrowheads) PRAP vanishes acutely before bristle elongation. Each nucleus is marked by Histone2B-ECFP (magenta) and is outlined by a dashed line. (M–Q) Panels are Y-Z sections of the cells shown in C, D, K, and L. pI cell shown in C corresponds to the cell in M. pIIa and pIIb cells in D correspond to N. The socket cell in K was shown in O, and the shaft cell in K was in P. Both socket and shaft cell in L was indicated in Q. Bar, 5 µm. (R) Schematic representation of PRAP dynamics from a pI cell (i.e., SOP cell) to bristle formation. (S) Sequential variation of Venus intensity in each cell type (so, orange; sf, green; n, blue; sh, red; g, purple). Three representative lineages are shown. (T) Endogenous DIAP1 protein is regulated post-translationally. The endogenous DIAP1 protein was detected in the socket and shaft cells, after the final precursor cell division. Bar, 5 µm. The genotype was neu-GAL4 UAS-Histone2B-ECFP/UAS-PRAP39.