Fig. 1.

Overview of the developmental organization of the Drosophila central complex. a Schematic drawing of Drosophila central complex (CX; antero-lateral view) and large-field neurons. Left: DALv2 ER-neuron as a representative of tangential neuron, providing input from the bulb (BU) to the ellipsoid body (EB). Right: PBp1 (Delta7) neuron as an example of an intrinsic neuron whose arbor is restricted to a CX compartment (here: protocerebral bridge, PB). b Schematic drawing of CX (dorsal view) depicting representative example of small-field (columnar) neuron, with arborizations restricted to narrow volumes (glomeruli, columns) of different CX compartments. Figures adapted from (Hanesch et al. 1989). c Schematic of a neuronal lineage formation and projection into different neuropil compartments (grey squares). Broad neuron classes of a lineage collectively tile a few compartments, referred to as the projection envelope of the lineage, within which, individual neuron types form various circuit motifs. d z-projection of frontal confocal sections of Drosophila brain at the level of the fan-shaped body (FB). GFP-labeled MARCM clone of the CP2/DL1 lineage, consisting of a dorsal (CP2d) and ventral (CP2v) hemilineage. Neuronal cell bodies are rendered in magenta, fiber tracts and arborizations in green. Lineage-associated tracts project in characteristic patterns, as shown here for CP2d neurons that follow the oblique posterior fascicle (obP) and then the longitudinal superior medial fascicle (loSM) to reach the FB. d’ Digital (in-silico) clone of CP2 neurons identified in the hemibrain database based on characteristic location and projection patterns. e Electron microscopy (EM) section of Drosophila brain showing CP2d axon bundle. Scale bars: 500 nm. f Schematic representation of CX and surrounding compartments, visualizing the topography of lineages that innervate the CX. Annotated on the left are neuropil compartments providing input to the CX: inferior bridge/superior posterior slope (IB/SPS), superior protocerebrum (SLP/SIP/SMP), anterior optic tubercle (AOTU) and bulb (BU), crepine (CRE) and lateral accessory lobe (LAL). Right half of the schematized brain shows lineages—represented by colored circles alongside their names. Position of circles roughly coincides with the location of somata clusters in the brain. Although the focus of our analysis are the large-field neurons, we also include the lineages which give rise to the small-field neurons (grey circles). Note: A novel finding from our hemibrain analysis is that the DM4 (DM1 and DM3 are hidden for brevity) lineages also give rise to a few large-field neurons. To distinguish the small- and large-field neurons of this lineage, we depict them as a separate yellow-colored circle in the right side of the schematic. Color-coded lines emanating from the different lineages interconnect the input domains of the constituent neurons with their output domains in the CX. The shading in the input domains reflects the degree of overlap (as in the SMP/SLP and CRE), or lack thereof (as in the AOTU and BU), of the arbors of the different lineages. The extension of the colored lines into the CX depicts the relative innervation patterns exhibited by these neurons. More detailed, and realistic, tract trajectories are schematized in the subsequent figures which highlight individual CX compartments. g Number of neurons (from both hemispheres) provided by different lineages (along vertical axis) to CX compartments (along horizontal axis). For other abbreviations see Table 1