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Figure 4 | Neural Development

Figure 4

From: Polycomb group genes are required to maintain a binary fate choice in the Drosophila eye

Figure 4

N is not required to maintain repression of Sens in R7s. (A) Model of Sens repression in R7s [25]. N is activated in R7 precursors in row 6, repressing Svp and directing R7 precursors toward either of two inner photoreceptor fates, R7 or R8. N also represses Sens in R7 precursors, causing them to become R7s. (B) Wild-type ommatidial development. R neurons express Elav (blue); R1, R3, R4, and R6 express Svp (magenta); and R8 expresses Sens (green). (C–C'') A wild-type larval eye disc after upshift to 31°C for 3.5 h. The dashed line in C–C'' lies along row 6. The box in C corresponds to panel C'. (C) Svp is expressed in R3 and R4 from row 4 onward and in R1 and R6 beginning in row 6. (C') Ommatidia in rows 6-10 contain four Svp-positive cells. White dashed circles indicate ommatidia in rows 7-8, and yellow dashed circles ommatidia in rows 10-11. (C'') Sens is expressed in R8s only. (D–E'') A N ts1 mutant larval eye disc after upshift to the non-permissive temperature, 31°C, for 3.5 h. D–E'' are images of the same eye disc. (D,D') Sens is expressed in extra cells within rows 0–3, consistent with N's role in specifying R8s [46]. (E,E') Svp is expressed as in wild-type until row 7. In rows 7–8 Svp is misexpressed in R7s (white dashed circles; arrows indicate ommatidia with Svp-positive R7s), since these R7s were in rows 5–6 during the temperature shift and never experienced N activation. However, from row 9 onward, Svp is never derepressed in R7s (e.g. yellow dashed circles in rows 10–11). (E'') From row 4 onward, Sens is never expressed in R7s, despite inactivation of N and lack of Svp. Scale bars are 10 μm.

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