ABSTRACT
Properly developed somatosensory circuits are critical for any animal to sense and interact with their
environment. The development of somatosensory circuits requires that each neuron within the circuit to correctly
position its axons and dendrites. This allows them to establish specific synaptic connections and for circuits to
assemble. Within somatosensory circuits, interneurons represent are the most numerous neuron type. The other
types are sensory neurons of the peripheral nervous system. In comparison to sensory neurons, interneurons
are under investigated due to lack of tools and knowledge about somatosensory circuit architecture. Molecular
factors, like temporal transcription factors and guidance cues, are known to regulate different aspects of neuronal
development, however the role of these molecular factors has not been deeply investigated in interneuron
dendrite development, synaptic partner selection, and circuit formation. I will test the central hypothesis that
temporal transcription factors regulate guidance receptor expression, and this establishes specific dendritic
morphologies and synaptic connections. To investigate this central hypothesis, in the Drosophila nerve cord, I
will be using the neuroblast 3-3 stem cell and the EL interneurons it generates as a model. In Aim 1, I will test
the working hypothesis in NB3-3, temporal transcription factors, Cas and Nab, activate different sets of guidance
cue receptors in its early-born and late-born EL daughter interneurons, and that this determines differential
dendrite positioning. I use single cell RNA-sequencing, NB3-3 specific gene manipulation of Cas and Nab, and
confocal microscopy to examine dendrite morphology. I expect to connect the role of temporal transcription
factors to the role of guidance cue receptor expression. Additionally, I expect to introduce an innovative
sequencing approach to our current analysis of somatosensory circuit development. In Aim 2, I will test the
working hypothesis that the guidance receptor Roundabout3 (Robo3) is necessary in early-born EL dendrites
and sufficient in late-born EL dendrites to regulate dendrite morphogenesis and position. I will perform Robo3
subcellular localization assays alongside gain and loss-of-function assays of Robo3 to examine the function of
Robo3 in EL dendrites. This aim will serve to identify the requirement of Robo3 in interneurons and develop new
assays to analyze Robo3 localization. Overall, this proposal will connect to previous disparate areas of
somatosensory circuit development. This work will also enable future research to investigate the broad
conservation of neuronal circuit specification and development of therapies for neurodevelopmental pathologies
in which circuit wiring is disrupted.
