Figure 9. Pnt-GFP and Yan expression in the larval eye imaginal disc.

(A–A″) Confocal projection of Pnt-GFP (green) and Yan (purple) in the developing eye disc. Position of the morphogenetic furrow (MF) is indicated, as are the ocelli (arrows). Insets show a magnified view of Yan and Pnt-GFP near the MF. (B) Diagram of an eye imaginal disc with the MF bisecting the undifferentiated anterior region (dark blue) and differentiating posterior region (light blue). Boxes outline the approximate locations of regions magnified in the subsequent panels of this figure. Letters inside boxes correspond to specific panels. (C–C‴) Expression of Pnt-GFP (C), Yan (C′), and Ato (C″) in a zone that spans the MF and includes cells at different stages of Ato expression, arrayed from anterior to posterior. The first stage has a broad band of anterior cells co-expressing low levels of Pnt-GFP and Ato (green arrow). At the onset of the second stage, Ato and Pnt-GFP expression increases, and some cells also begin to express Yan (cyan arrow). This stage has intermediate groups (IGs) expressing high levels of Ato and Pnt-GFP but not expressing Yan (white arrowhead). The cells between each IG express no Ato, but do express high levels of Pnt-GFP and increased levels of Yan (orange arrow). Two or three posterior cells in each IG express the highest level of Ato, and these cells are the R8 equivalence group (yellow arrowhead). The third stage has a single Ato-positive cell, which is fated to become the R8 cell (white arrow). Pnt-GFP levels remain high or even increase in this cell, while Yan is not detected above background. The merge (C‴) shows Pnt-GFP (green), Yan (red) and Ato (blue) in the same image. (D–D″) Expression of Pnt-GFP (green) and Yan (purple) in uncommitted precursor cells posterior to the MF. Highlighted 1 and 2 are two successive regions of induction of Pnt-GFP (these do not correspond to the stages of Ato expression described in C). Note that Yan is broadly expressed in precursors and is upregulated in the zone spanning the two regions of Pnt-GFP induction. More posterior, the precursor cells lose Pnt-GFP. (E–E″) Expression of Pnt-GFP (green) in cells within the second wave of induction (left) and in differentiating photoreceptors (right). The protein is primarily nuclear (purple). All images are oriented anterior-left and dorsal-up.