Expression of Poxn and D-pax2 is lacking in NBs of the IZ. (a,b) D-pax2/En-lacZ double stainings; flat preparations of late stage 11 (lst11) embryos. (b) Magnification of boxed area in (a) at the level of NBs. En-lacZ-positive NBs deriving from the antennal en stripe (as; Dv8, Dd5) and en head spot (hs; Ppd5,8) are indicated. D-pax2 is detected in SOPs of the dorsal organ (blue arrowhead), the hypopharyngeal/latero-hypopharyngeal organ (green arrowhead), and of the labral sensory organ (yellow arrowhead in (a)) . Note that SOPs at positions corresponding to those of the dorsal organ within the developing antennal appendage (AN; outlined by black dashed line) are also found in the appendage of the mandibular and maxillary segment (white arrows in (a)). (c) D-pax2 stained whole mount embryo at stage 15 (st15) with a focus on the brain (outlined by the white dashed lines). D-pax2 is found in the respective sensory organs. (d-h) Poxn/En-lacZ double stained embryos. (d) Late stage 11 (lst11). Few Poxn-positive cells contribute to the labral (yellow arrowhead) and antennal (blue arrows) sensory organs. Poxn sensory founder cells arise at corresponding positions in the antennal, mandibular, maxillary, and labial segments (white arrows), immediately anterior to the respective en stripes. Note that in the CNS, Poxn expression is not yet initiated. (e) Close-up of boxed area in (d). Poxn expression initiates in peripheral ectodermal cells (group 1, 2) positioned in the antennal appendage, which are likely to contribute to the antennal dorsal organ. (f) By stage 12/4, Poxn expression comes up in cells of the DC (group 3) immediately anterior to the antennal en stripe (as). (g) By stage 13, first en-coexpressing cells (group 4), descending from the two head spot (hs) NBs, initiate Poxn expression. Note that the head spot NBs are Poxn-negative. (h) Stage 16. The number of Poxn-positive cells in the deuto- and protocerebral cell cluster is increased. (i) Summary of D-pax2 expression at late stage 11 in SOPs (orange) of the hypopharyngeal organ (Dv1,3) and the dorsal organ (Dd9,11,12). Other abbreviations are as in Figure 1.