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Fig. 6. Histoblast proliferation and LEC death are triggered by Ecdysone
signaling. (A) Blocking Ecdysone signaling autonomously in
histoblasts abolished their proliferation. The overexpression of an Ecdysone
receptor EcR-RNAi construct (Esg-Gal4) results in a prolonged delay in cell
division. The left image shows a dorsal anterior nest at the prepupal stage
expressing EcR-RNAi. The number of histoblasts in this nest is similar to
equivalent nests in wild-type pupae (see
Fig. 1B). The middle image
shows the same nest 300 minutes later; histoblasts have not divided. In this
period, wild-type animals undergo three rounds of division (right image).
(B) Clonal autonomous inhibition of Ecdysone signalling in LECs
(dominant-negative form of the Ecdysone receptor EcR-DN) blocks their death
(see Materials and methods). The left image shows a control animal in which
the abdominal epithelial fusion proceeds normally. As a result of the
overexpression of EcR-DN (middle image) the expansion of histoblast nests does
not succeed, resulting in a dorsal scar phenotype (arrowheads). Simultaneous
expression of a GFP marker reveals that LECs (asterisk) have not been
eliminated from the abdomen of pharate adult mutant flies (green: right
image).