Molecular control of stochastic color vision circuit assembly

Project Summary
Diverse neuronal types are specified into correct cell fates and connected with proper targets during circuit
formation. Over the last decades, a number of cell surface molecules have also been identified that mediate
axon guidance and connectivity. However, little is known about the coordination between neuronal
specification and specific connectivity patterns, especially when two synaptic partners undergo two different
modes of cell specification (stochastic vs. deterministic). The Drosophila color vision circuit is an appealing
model to address this question mechanistically due to our deep knowledge of its development and neuronal
connectivity, where Dr. Chen’s primary mentor, Dr. Claude Desplan, at New York University has been a
leading expert in this field. In the fly retina, yellow (y) and pale (p) subtypes of color photoreceptors (R7 and
R8) are stochastically specified, whereas their synaptic partners in the optic lobe are produced through highly
deterministic programs. The first aim (K99) of this project is to characterize the y/p columnar stochastic circuits
in the higher brain regions. Dr. Chen will perform EM connectomic analyses under the training of Dr. Michael
Reiser to reconstruct the color vision circuit. Dr. Chen will also make highly cell-type-specific developmental
driver lines for gaining genetic access to the cell types of interest. High-resolution transcriptomes for neurons
downstream of either y or p pathway will be generated via Tango-seq under the mentorship of Dr. Chen’s
collaborator, Dr. Justin Blau. The second aim (K99) of this project is to identify molecules required for synaptic
partner matching. In collaboration with Dr. Graeme Mardon, Dr. Chen has accessed and used the single-cell
RNA sequencing (scRNAseq) datasets of both developing retina and optic lobes to identify promising
candidates that mediate synaptic connectivity of y/p neuronal subtypes. Dr. Chen will be trained by Dr. Robin
Hiesinger to perform ex vivo live imaging of developing optic lobes to identify the functional role of these
candidate molecules in synaptic partner matching. The third aim will be performed in Dr. Chen’s independent
lab (R00) to study how the synaptic partner choices propagate to neurons further downstream by perturbating
the cell fates of R7 and R8. Dr. Chen will compare whether a given neuron uses the same or different
molecular codes for matching its pre- and post-synaptic partners. Successful completion of this proposal will
uncover novel molecular mechanisms regulating synaptic pairing and probe the fundamental principles
underlying the propagation of cell fate choices during circuit assembly. The principles identified here will be
significant and applicable to other neuronal circuits facing similar developmental challenges, such as the
olfactory system in rodents and color vision in humans. To achieve Dr. Chen’s career goal of becoming an
independent scientist in a leading research university, Dr. Chen has assembled a great mentoring team,
including Dr. Claude Desplan and Dr. Jeremy Dasen (co-mentor), as well as his advisory team to ensure a
successful career and scientific progression during the funding period.
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Grant Number: 5K99EY035757-02
NIH Institute/Center: NIH
Principal Investigator: Yu-Chieh Chen