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Fig. 3. Robo receptors regulate targeting of olfactory neurons to specific
glomeruli. Lobes are oriented as indicated in C,F: M, medial; D, dorsal; V,
ventral. Imaging was carried out from anterior to posterior and a few 1 µm
confocal sections are stacked in each picture. (A) Olfactory lobes of
or22a-Gal4;UAS-N-SybGFP stained with mAbnc82 (red). Or22a-expressing
neurons project to a single glomerulus DM2 and also cross over in the
inter-antennal commissure (arrow). (B,D,E) The MARCM method was used to
positively mark neurons mutant for robo21 (B) or
robo31 (D,E). Axons lacking Robo2 function terminate
within the midline creating a `roundabout' appearance (arrowheads in B;
diagram in C). Ectopic axonal arbors are immunoreactive for mAbnc82 (arrow in
B). Axons lacking Robo3 function terminate aberrantly (broken lines in D,E;
diagram in F). (G-L) Sensory neuron terminals in the olfactory glomeruli are
visualized using a SG18.1-UAS-GFP recombinant strain in different
conditions. (G,J) Appropriate confocal sections have been selected to
visualize normal glomeruli (G, *) and antennal commissure (J,
arrow). (H) SG18.1 UAS-GFP/UAS-comm. (I) SG18.1
UAS-GFP/UAS-abl. In both H and I, glomerular patterning is significantly
disrupted while the antennal commissure is present (arrow), although axons
appear somewhat loosely fasciculated. (K,L) SG18.1
UAS-GFP/UAS-Dcdc42v12 (constitutively active). Glomeruli
cannot be discerned within the lobes (K). The commissural region (boxed in K)
is examined at better resolution in L. Stacking of fewer sections shows a
clear glomerular-like organization (*) within the commissure.