The Drosophila neural lineages: a model system to study brain development and circuitry

Abstract

In Drosophila, neurons of the central nervous system are grouped into units called lineages. Each lineage contains cells derived from a single neuroblast. Due to its clonal nature, the Drosophila brain is a valuable model system to study neuron development and circuit formation. To better understand the mechanisms underlying brain development, genetic manipulation tools can be utilized within lineages to visualize, knock down, or over-express proteins. Here, we will introduce the formation and development of lineages, discuss how one can utilize this model system, offer a comprehensive list of known lineages and their respective markers, and then briefly review studies that have utilized Drosophila neural lineages with a look at how this model system can benefit future endeavors.

Fig. 1

Lineage development from larva to adult. Cartoon diagram highlighting a single neural lineage in the third instar brain (left) and in the adult brain (right). Note the decreased contribution of primary neurons in the adult brain compared to the third instar brain. GMC ganglion mother cell

Fig. 2

Drosophila lineage properties. Cartoon diagram contrasting a bipolar vertebrate neuron (a) and a unipolar Drosophila neuron (b). Dendritic arbors are shown in orange and axonal terminals are colored green. Dendrites are segregated from axons in neurons with proximal-distal branching (PD), while pre-synaptic and post-synaptic branches are mixed in continuous (c) and distal (d) branching patterns. mcd8GFP expression (c, e) versus proximal localization of the dendritic marker DSCAM1.1:GFP (d, f) in adult preparations of two lineages: BLD5 visualized with atonal-GAL4 (c, d) and DALv2 visualized with EB1-GAL4 (e, f). Axonal visualization, or lack thereof, is labeled with a white arrow

Fig. 3

Secondary versus primary arbor patterning. A schematic diagram representing the widely dispersed projections of the embryonic-born primary neurons (blue/purple) versus the localized branching of larval-born secondary neurons (orange) in the ventral nerve segments

Fig. 4

Lineage-based clonal analysis. Cartoon diagram explaining the genetic technique of mosaic analysis with a repressible cell marker (MARCM; top) and flip-out induced clones (bottom). MARCM clones are generated by inducing recombination at FRT sites during the G2 phase of mitosis through conditional expression of flipase under the control of the hsp-promoter. Upon division, recombined chromosomes are segregated so that one daughter cell contains both copies of GAL80 and the other lacks inhibition of the GAL4 system. If the neuroblast loses the GAL80 transgene, all subsequent divisions generate neurons that express GAL4-driven GFP expression. Flip-out clones are generated by flanking a termination sequence (double red bar) with FRT sites between the promoter/enhancer and the GAL4 transgene. Upon conditional expression of flipase via a brief period of heat shock, the termination sequence is extracted by recombination of the FRT sites, and GAL4 protein is produced, allowing for marker expression under control of an upstream activating sequence (UAS). If the termination sequence is extracted from the neuroblast, all further progeny from that neuroblast will express the marker protein

Fig. 5

3D digital models of all lineages in one brain hemisphere. Top anterior view, bottom posterior view. For both models, the superficial region of the cortex was “sliced off” to allow for clearer view of lineages. Lineages are annotated according to Pereanu and Hartenstein (2006)

Fig. 6

Assortment of lineage markers. a Right hemisphere of a third instar brain labeled with anti-Neurotactin (BP106, green) and anti-DNCadherin (magenta). b Volume rendering of an adult brain with GFP expression under the control of GH146-GAL4. Visualized lineages include BAla1, BAmv3, and mushroom body lineages. c Right hemisphere of a third instar brain with lacZ expression in the DALv3 lineage under the control of the engrailed promoter. d MARCM induced clone in the Adult BAla1 lineage (inset shows third instar clone), visualized under the control of the period-GAL4 driver. All neuropiles are labeled with anti-DNcadherin (magenta). In all panels, medial is to the left and dorsal is up. SAT secondary axon tract, AL antennal lobe, LH lateral horn, MB mushroom body