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. Author manuscript; available in PMC: 2014 Jul 1.
Published in final edited form as: Wiley Interdiscip Rev Dev Biol. 2012 Nov 16;2(4):545–557. doi: 10.1002/wdev.100

Figure 4. Progression of the morphogenetic furrow.

Figure 4

(A) is a diagram showing that Hh expressed in developing photoreceptors activates a stripe of dpp expression in the morphogenetic furrow. Dpp then acts at a long range to repress hth, limiting it to the anterior of the eye disc and establishing a preproneural zone (PPN) in which cells can respond to Hh. (B) shows regions of third instar eye discs stained for the indicated markers. Elav is a neuronal-specific protein used to mark differentiating photoreceptors. (C) is a diagram of the five signaling steps involved in recruitment of each photoreceptor or photoreceptor pair to the forming ommatidium. Rho proteins expressed in R8, R2 and R5 allow these cells to produce Spi, which is instrumental in recruiting all photoreceptors other than R8. Dl produced by R1 and R6 and Boss produced by R8 are also necessary to recruit R7.