Fig. 2. Expression of segment polarity genes at embryonic stage 11 (st11). (A,C,E,G) Left half of head flat preparations double labelled for segment polarity gene expression and en-lacZ, invected (inv) or ladybird (lbe); focus is on the peripheral head ectoderm; broken line marks the ventral midline; insets depict lateral views of stage 11 whole-mount preparations. (B,D,F,H) Close-ups of regions indicated in A,C,E,G by black frames; focus is on the level of NBs; immunopositive NBs are indicated by white inscription, immunonegative NBs are indicated by black inscription. (A,B) Only part of the antennal/ocular hh-lacZ domain co-expresses inv. Note the strong hh-lacZ signal in the dorsal Ppd5, Ppd8, Ppd10, Ppd11, Ppd15 and Ppd16. (C) gsb-d is downregulated in the ocular neuroectoderm, and is detectable in four tritocerebral NBs deriving from the gsb-d intercalary stripe, and in three deutocerebral NBs deriving from the gsb-d antennal stripe (D,I,J). (E,F) mirr-lacZ expression shows no segmental pattern and is mainly limited to the ventral part of the PNR and corresponding NBs. (G) lbe is segmentally expressed in the procephalic neuroectoderm [arrows; for details, see Urbach and Technau (Urbach and Technau, 2003)], where it is co-expressed with wg, except in the wg hb and wg fg. (H) lbe is co-expressed with wg in Dd7 but not in the ocular Ppv3 and Pcv8. (I) Segment polarity gene expression in identified brain NBs at stage 11; nomenclature of brain NB has been described previously (Urbach et al., 2003). Colour intensity reflects weak () and strong (+) expression levels of inv, hh-lacZ and wg. Stars indicate mandibular NBs. (J,K) Segment polarity gene expression in the peripheral procephalic ectoderm. (L-N) inv expression in the dorsal hemispheres (dh). (L) Lateral view of late stage 11 head, showing a faint inv expression in the dh. Note that en expression in the dh is not detected using en-lacZ and was only observed with anti-Inv antibodies from late stage 11 onwards. (M) Left half of a head flat preparation. The dh comprises about 10 Inv-positive NBs (as depicted in I). (N) inv expression in the brain and sub-oesophageal ganglion (SOG) of a stage 16 embryo (horizontal view). Note, that Inv staining in the dh corresponds to the pars intercerebralis of postembryonic stages. The secondary head spot (shs) marks a small group of cells which secondarily separates from the hs (see Schmidt-Ott and Technau, 1992). 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; dh, en expression in the dorsal hemispheres; hs, en head spot; is, en intercalary stripe; shs, en secondary head spot; gsb-d as, gsb-d antennal stripe; gsb-d is, gsb-d intercalary stripe; gsb-d lr, gsb-d labral spot; wg as, wg antennal stripe; wg fg, wg expression in the foregut; wg hb, wg ocular head blob; wg is, wg intercalary spot; wg lr, wg labral spot.

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