Form and function of the secondary hemilineages in the adult Drosophila thoracic nervous system
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The majority of the neurons in the adult Drosophila thoracic nervous system are produced by one unpaired and twenty-four bilaterally paired, segmentally reiterated neuroblasts (NBs). Each neuroblast divides repeatedly, producing a series of ganglion mother cells. Each ganglion mother cell, in turn, divides to form 2 daughter neurons, one that is Notch-on and the other Notch-off. Collectively, the Notch-on neurons are called the "A" hemilineage, and their Notch-off siblings are the "B" hemilineage. Neurons within a hemilineage extend initial neurites to the same stereotyped location, then arrest development until the onset of metamorphosis. It seems reasonable, based on their common developmental origin and very similar larval morphology, to hypothesize that neurons within a hemilineage could share functional properties in the adult. In this thesis, I describe a set of genetic reagents to direct gene expression to these hemilineages in the adult (Chapter 2), characterize their adult morphology (Chapter 3), and document the behaviors induced by activating them using the conditional transgenic neural activator TRPA1 (Chapter 4). I find that the neurons within a secondary hemilineage occupy a unique space in the thoracic neuropil, and cause a characteristic combination of behaviors when activated. This supports the hypothesis that these neurons are functionally related and paves the way for future investigation.