Fig. 1. Expression of segment polarity genes at embryonic stages 9 (st9) and 10 (st10). Colour code indicates the expression pattern of engrailed-lacZ/Invected protein (en/inv; red), hedgehog-lacZ (hh; purple), mirror-lacZ (mirr; blue), wingless-lacZ/Wingless protein (wg; green), and Gooseberry-distal protein (gsb-d; pink) at the level of identified brain NBs (A,D) and procephalic neuroectoderm (B,C,E,F). All panels show semi-schematic representations of a ventral view of the left half of head flat preparations; anterior (a) is towards the top and dorsal (d) is towards the left. Nomenclature of brain NBs is according to their position in the trito- (T), deuto- (D) and protocerebrum (P) [for details of the nomenclature see Urbach et al. (Urbach et al., 2003)]. In (B,C,E,F), thick hatching marks strong expression and thin hatching marks weak expression of the respective gene; for comparison, NBs underlying the peripheral ectoderm are encircled by broken lines. The expression of en, gsb-d and wg is confined to intermediate and dorsal brain NBs (A,D) and corresponding sites of the peripheral procephalic ectoderm (B,C,E,F). By stage 10, Gsb-d is detected in the ectoderm of all four pregnathal head segments (E). In the gsb-d ocular domain (gsb-d oc) and two corresponding NBs (Ppd3, Ppd10) gsb-d expression is transient (compare with Fig. 2). It is also transiently expressed (between stages 10 and 11) in the clypeolabral ectoderm [in the gsb-d labral spot, which is partly colocalized with the wg labral spot (E)] from which no NBs emerge (see also Fig. 2). mirr-lacZ is not segmentally expressed in the procephalic neuroectoderm; it is observed in the invaginating foregut and flanking neuroectoderm, and is additionally detected in a more intermediate ectodermal antennal spot (from which Dd6 arises). A large wg domain extends from the antennal into the ocular head region (B), but later separates into an antennal stripe (wg as) and ocular head blob (wg hb) (E). hh-lacZ expression accumulates in posterior regions of the antennal and ocular ectoderm (F; see also Fig. 2J). (A,D) Note that a large number of identified brain NBs (especially protocerebral) do not express any segment polarity gene. For a detailed description, see text. Stars indicate mandibular NBs. as, en antennal stripe; CL, clypeolabrum; FG, foregut; gsb-d as, gsb-d antennal stripe; gsb-d is, gsb-d intercalary stripe; gsb-d lr, gsb-d labral spot; gsb-d oc, gsb-d ocular domain; hs, en head spot; is, en intercalary stripe; ML, ventral midline; wg as, wg antennal stripe; wg lr, wg labral spot; wg fg, wg expression in the foregut; wg is, wg intercalary spot.; wg hb, wg ocular head blob [for nomenclature of en and wg expression domains in the procephalic ectoderm, see Schmidt-Ott and Technau (Schmidt-Ott and Technau, 1992)].

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