Figure 2.
fra Is Required in R Cells to Regulate R8 Axon Targeting to the M3 Layer
(A and A′) In controls, Rh6-lacZ-positive R8 axons (blue) target to the M3 layer in the medulla (Me) (double arrowhead in A′). La, lamina.
(B and B′) In ey3.5-FLP mosaic animals lacking fra in R cells, many R8 axons stall at the medulla neuropil border (arrows) or terminate incorrectly in the M1/M2 layers (arrowheads).
(C) Quantification of phenotypes is shown.
(D–E″′) A fra mutant, GFP-positive R8 axon generated by MARCM terminates incorrectly in M1/M2 (arrowheads). The area outlined in (D) is shown at higher magnification in (E)–(E″′).
(F–G′) At 24 and 42 hr APF, all R8 axons expressing ato-τ-myc (blue) terminate in their temporary layer at the medulla neuropil border in controls (double arrowheads in F′ and G′).
(H and H′) At 55 hr, all R8 axons proceed to the M3 layer in the medulla neuropil in controls (double arrowheads).
(I–J′) In animals lacking fra in R cells, the majority of R8 axons pause at the medulla neuropil border, whereas a small percentage prematurely projects deeper (arrowheads).
(K and K′) In fra ey3.5-FLP mosaics, many R8 axons fail to enter the medulla neuropil (arrow) or terminate prematurely in the M1/M2 layers (arrowhead).
(L–N) Quantification of phenotypes is presented.
(O–P′) Overexpression of fra in R cells causes stalling of Rh6-eGFP-positive R8 axons (green) at the medulla neuropil border (arrows in P and P′), when compared to controls (double arrowheads in O and O′). R7 axons (red) are not retargeted to the M3 layer but occasionally show small extensions into deeper layers (arrowheads in P and P′).
(Q) Quantification of phenotypes is shown. R cells are labeled with mAb24B10 (red).
Scale bars, 20 μm.
See also Figures S2 and S3.