Fig. 4. Expression of the early eye genes dac, ey and toy at embryonic stages 9, 10 and 11. Semi-schematic presentation of Dachshund (dac), Eyeless (ey), and Twin of eyeless (toy) expression in brain NBs [A-C; low () and high (+) expression levels; red lines indicate neuromeric boundaries], and within the outer procephalic ectoderm (D-F; thick hatching indicates strong expression, thin hatching indicates weak expression) as indicated at stage 9 (st9, A,D), stage 10 (st10, B,E), and stage 11 (st11, C,F). Engrailed (en) expression domains in the peripheral ectoderm are indicated for comparison. (G-L) Double staining for expression of svp-lacZ (G-J) or en-lacZ (K,L), and Dachshund (dac; G,H), Eyeless (ey; I,J) and Twin of eyeless (toy; K,L). (G,I,K) Outer procephalic ectoderm of flat preparations (dashed line indicates ventral midline); insets show lateral views of stage 11 wholemounts. (H,J,L) Higher magnifications of regions indicated by frames in G,I,K at the level of brain NBs. (G) Red arrow indicates the intercalary Dac-positive ectodermal domain including the Dac-positive NB Tv2. (I,J) Ey is expressed in few NBs; Ey/en-lacZ double labelling (see inset on bottom left in I) shows Ey expression in the intercalary and antennal head immediately anterior to the respective en domains (arrows). (K,L) Toy is mainly confined to protocerebral NBs and to Dd8. Anterior (a) is towards the top; dorsal (d) is towards the left (except for insets). AN, IC, MD, MX, antennal, intercalary, mandibular and maxillary segment, respectively; CL, clypeolabrum; FG, foregut; ML, ventral midline; OA, Bolwig organ/optic lobe anlagen; as, en antennal stripe; hs, en head spot; is, en intercalary stripe.

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