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The mapping of neurons and lineage classification of the larvae and adult Drosophila brain in several Gal4 transmitter lines

Abstract

In Drosophila, neurons within the central nervous system are grouped into units called lineages. Each lineage contains cells derived from a single neuroblast. A neuroblast is a stem cell divides and forms lineages of neurons. In flies, the lineage can be subdivided into different parts; the neurons that are born first are closest to the neuropile (Spindler and Hartenstein, 2010). There is a birth ordering of neurons. In the embryo, the neuroblasts divide 5 to 6 times and are called primary neurons. In the larvae, we are able to still see primary neurons, but each neuroblast divides further and undergoes about 50 divisions and these cells are termed secondary neurons. There is a small population of primary neurons and a huge population of adult secondary neurons in Drosophila. The secondary neurons are known to use the primary neurons as their guiding path.

My project addresses the relationship of nerve fibres (axons and dendrites) formed by primary and secondary neurons in the brain neuropile. I am using a marker expressed in a subset of primary lineages, called Fasciclin II (FasII), and another marker expressed in all secondary neurons, called Neurotactin. In one set of experiments I am using a Gal4 driver line expressed in the FasII-positive neurons to ablate these cells, and study the effect on the pathfinding of BP106-positive secondary neurons. To that end I have crossed the FasII-Gal4 line to a UAS-hid;rpr construct that will induce cell death. My preliminary results show that the animals die already as embryos, possibly due to neural defects. I am currently investigating the neuronal basis for this early cell death (which precludes me from analyzing secondary neurons). A second project is to assign a large collection of published single neuron clones (insert reference) to the groups of primary vs. secondary neurons. The clones were induced using driver lines expressed in neuron populations expressing different neurotransmitters (such as TH-Gal4, Cha-Gal4). I will use the lines and express a GFP reporter, in addition to BP106, at different developmental stages. This will allow me to determine whether a given line/transmitter is expressed in primary neurons, secondary neurons, or both; and will also allow me to map the neurons to specific lineages.

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