Fig.1.

Pattern of long axon tracts connecting the brain and ventral nerve cord of the early first instar larva. A-D: Z-projections of confocal sections of brains labeled with anti-FasII in horizontal orientation; anterior is to the top. A shows a low magnification of the entire brain and ventral nerve cord. Note the continuity of the evenly spaced long fiber fascicles of the nerve cord (vcfs) through the cervical connective (ct) into the brain neuropile (brnnp). B-D are high magnification images of the right brain hemisphere. Each Z projection in B-D corresponds to a horizontal brain slice of approximately 20 microns; the mid-levels of the slices are indicated at left margin of panel J. B represents the level of the central brain, containing the mushroom body [dorsal lobe (dl); medial lobe (ml); peduncle (ped), spur (sp), calyx (CX)] and antenno-cerebral tract (ACT). C shows basal brain level, D the level of the cervical connective. E-I: Histological frontal sections of brain labeled with anti-Fasciclin II. Sections contain right brain hemisphere (lateral to the left, dorsal up) and are 3 microns thick. Levels of sections are indicated at lower margin of panel J. E shows section of antenno-cerebral tract in front of calyx; F and G are taken at level of calyx and show the medial and lateral cervical tracts (MCT, LCT), respectively. H shows level of optic lobe (OL) and posterior cervical tract (PCT). I shows level posterior to optic lobe and illustrates spatial arrangement of the longitudinal axon tracts in the ventral nerve cord. J-L: Digital 3D models of brain hemisphere in medial view (J), dorsal view (K) and dorso-medial-posterior view (L). In these models and the models of the following figures, systems of long axon tracts are shown in different colors: the medial cervical tract (MCT) is red, the lateral cervical tract (LCT) with its branches [central anterior protocerebral tract (CAPT), ACT, basomedial protocerebral tract (BMPT)] is blue, the posterior cervical tract (PCT) and its branches [dorsoposterior protocerebral tract (DPPT), basolateral protocerebral tract (BLPT)] green. The color of ventral nerve connectives hints at the cervical tracts they give rise to: the dorso-medial tract (DMT) contributes axons to all three cervical tracts (see also panels D, H) and is colored brown; the ventro-medial tract (VMT) is colored purple because it contributes to the medial and lateral cervical tract (see also panels D and G). The dorso-lateral and central-intermediate tracts (DLT, CIT) give rise to the posterior cervical tract (green; see panels D and H); the dorso-intermediate (DIT) and part of the centro-intermediate system contributes to the lateral cervical tract (blue). In all three panels, the mushroom body and optic lobe are shown in gray as landmarks. In J and K, neuropile compartments are shown in semi-transparent gray. M-Q: Z-projections of horizontal confocal sections of brain hemispheres labeled with anti-FasII (red) and a marker for neuropile (UAS-GFP driven by Chat-Gal4; Salvaterra and Kitamoto, 2001) in green; anterior is to the top. The levels of sections are indicated at left margin of panel J. M represents the level of the dorsal brain [dorsal lobe of mushroom body (dl), calyx (CX), dorso-anterior and dorso-posterior compartments (DA, DP)]. N is taken at central brain level, with peduncle (ped), medial lobe (ml), centro-anterior compartment (CA), centro-intermediate compartment (CPI), and centro-lateral compartment (CPL). O corresponds to basal brain level (baso-anterior compartment = antennal lobe, BA; baso-central compartment BC; baso-posterior medial compartment BPM; baso-posterior lateral compartment BPL). Note position of main long axon tracts (MCT, ACT, BMPT, BLPT) relative to compartment boundaries. P and Q show sections at level of cervical connective at the transition between brain and ventral nerve cord (vc) Other abbreviations: es esophagus; OL optic lobe; MeB median bundle; VAC ventral anterior commissures

Bars: 10μm (for A; B-D; E-I; M-Q)