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The EGF receptor and notch signaling pathways control the initiation of the morphogenetic furrow during Drosophila eye development

Department of Cell Biology, Emory University School of Medicine, 1648 Pierce Drive, Atlanta, GA 30322-3030, USA

View larger version (52K): [in a new window]   Fig. 1. Egfr in furrow birth and reincarnation. (A) Time line describing critical periods. Initiation of the furrow estimated to occur at 184-186 hours after egg deposition (AED; red line). Two temperature-sensitive points (TSPs) for Egfr: TSP1 is 168-180 hours AED; TSP2 is 192-204 hours AED. (B-D) SEMs: (B) wild type; (C) TSP1 (note only non-ommatidial bristles are present); (D) TSP2 (note normal facets at posterior margin; white arrow). (E-J) Discs labeled with phalloidin, which shows F-actin (red), and -Elav, which shows photoreceptors (green). (E-G) Wild type. (H-J) Upshifted Egfrtsla/EgfrtopCO. (E) 180 hour AED; before furrow initiation. (F) 192 hours AED; newly initiated furrow and single column of ommatidia. (G) 204 hours AED; further progression of furrow. (H) TSP1 dissected at 192 hours AED; compare with wild type in F. (I) TSP1 dissected at 204 hours AED; furrow still not initiated, compare with wild type in G. (J) TSP2 dissected at 204 hours; birth normal but reincarnation inhibited. Anterior is towards the right. White arrows in F,G,J indicate furrow.

View larger version (122K): [in a new window]   Fig. 2. Egfr signaling is sufficient to induce furrow initiation. (A) Diagram of dppblk-GAL4 expression. (B-P) Expressed proteins as shown in each panel. Arrows show ectopic furrows, arrowheads indicate furrow inhibition. Anterior is towards the right; F-actin is in red; Elav in green. (F,N) Dorsal and ventral furrows nearly fill the entire eye.

View larger version (29K): [in a new window]   Fig. 3. dppblk-GAL4 controls expression along the posterior-lateral margins of the developing eye imaginal disc. (A,B) dppblk-GAL4/UAS-lacZ. (C) dppblk-GAL4/UAS-Egfr[act]/UAS-lacZ. (A) L2 eye-antennal imaginal disc. (B,C) L3 eye-antennal imaginal disc. Anterior is towards the right; F-actin is in red; lacZ in green. lacZ levels are elevated along the dorsal and ventral margins are sites of ectopic furrow initiation.

View larger version (79K): [in a new window]   Fig. 4. Receptor tyrosine kinase specificity. Expression of proteins named in each panel controlled by dppblk-GAL4. Driven proteins are indicated in each panel. Anterior is towards the right; F-actin is in red; Elav in green.

View larger version (56K): [in a new window]   Fig. 5. Notch is essential for furrow initiation. Arrows show ectopic furrows, arrowheads indicate furrow inhibition. Anterior is towards the right; F-actin is in red; Elav in green. (A) Wild type, asterisk shows furrow. (B-H) Expression of proteins named in each panel controlled by dppblk-GAL4. (B-D,G-H) Only reincarnation affected. (E) Ectopic furrow; this is the only E(spl)C protein that affects furrow initiation.

View larger version (73K): [in a new window]   Fig. 6. Notch, Egfr and Wg signaling pathways intersect to regulate furrow initiation. Expression of proteins named in each panel controlled by dppblk-GAL4. Arrows show ectopic furrows, arrowheads indicate furrow inhibition. Anterior is towards the right; F-actin is in red; Elav in green. (A) Both birth and reincarnation affected. (B-D) Ectopic furrows. (E,F) Only reincarnation affected.

View larger version (94K): [in a new window]   Fig. 7. Ectopic furrows behave like the endogenous furrow. (A,A',D,D') wild type. (B,B',E,E') Egfr[act] expression is controlled by dppblk-GAL4. (C,C',F,F') Egfrtsla. Genotypes listed above each column and protein visualized is noted to the left of each row. (A'-F') Single channels showing localization of Dpp and Wg antigen. (A-F) F-actin (red), detected proteins (green). Arrows in A-C,A'-C' indicate Dpp expression in the furrow. Note that Dpp expression is within cells of the ectopic furrows in B,B'. Arrows in D-F,D'-F' indicate Wg expression. Note that in (E,E') the ectopic furrow has initiated despite the presence of Wg at the margin and in (F,F') Wg expression is seen in the furrow if Egfr signaling is removed.

View larger version (26K): [in a new window]   Fig. 8. Models for furrow birth and reincarnation. Green arrows show inductive interactions, red symbols show inhibitory influences. Purple arrows and Hh in birth model indicates first ommatidial induction and purple ommatidia are the first ones produced. Blue furrows and arrows indicate Hh progression signal from the newly established ommatidia, and blue ommatidia are those produced by this mode of Hh induction. Orange arrows show progressive furrow re-initiation along the lateral margins and orange ommatidia are those induced by Dpp.