Fig. 2. Expression of gap genes at embryonic stage 11 (st11). (A-L) Left half of head flat preparations double stained for expression of a gap gene and en/inv (lacZ or antibody staining) as indicated. Pictures on the left (A,C,E,G,I,K) focus on the peripheral procephalic ectoderm; broken lines indicate the ventral midline; insets depict lateral views of stage 11 whole-mount heads. Middle panels (B,D,F,H,J,L) show close-up views of regions indicated in A,C,E,G,I,K by black frames; the focus is at the level of NBs. Positively stained NBs are indicated by white labels, negative ones are indicated by black labels. (A,B) Ems/en-lacZ. (C,D) Hb/en-lacZ. (E,F) hkb-lacZ/Inv. (G,H) Otd/en-lacZ. Note that Otd is expressed in the ventral midline, in a small domain within the ventral intercalary ectoderm (red arrow) and in cells along the dorsal midline (red arrowheads). (I,J) tll-lacZ/Inv; high level (HL) and low level (LL) tlllacZ-expression is indicated. (K,L) Slp1/en-lacZ. (M) Summary of gap gene expression in brain NBs as indicated by the colour code, which distinguishes between weak () and strong (+) expression of tll- and hkb-lacZ, and Slp1. Red lines mark the boundaries between tritocerebrum, deutocerebrum, ocular and putative labral neuromer. Stars mark mandibular NBs. (N-P) Semi-schematic presentation of gap gene expression in the peripheral procephalic ectoderm. (N) ems ectodermal domains are numbered (1-5), 3a and 3b derive from intercalary ems domain 3 (compare with Fig. 1B,F). Anterior (a) is towards the top; dorsal (d) is towards the left. 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; cl, en expression in the clypeolabrum; hs, en head spot; is, en intercalary stripe; mds, en mandibular stripe; slp1 as, slp1 antennal stripe; slp1 is, slp1 intercalary stripe; slp1 oc, ocular slp1 domain; slp1 lr, labral slp1 domain.

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