PROJECT SUMMARY/ABSTRACT
The regulation of transient cell behaviors and regulatory “states” is indispensable for the development
of multicellular organisms. Knowledge of the genetic architecture and emergent properties of these
processes is also key to developing therapies for congenital diseases and neurodevelopmental
syndromes based on cellular reprogramming or genome editing. The objective of this proposal is to
characterize the regulation and functions of potentially important genes that control polarized neuronal
migration and axon outgrowth in the Ciona larval nervous system, which shares many anatomical and
molecular features with the larger systems of their close relatives the vertebrates. The central
hypothesis is that these processes are controlled by precise developmental regulation of genes
encoding rate-limiting components of diverse biochemical pathways, which may vary according to
developmental stage and neuronal subtype. The rationale underlying the proposed research is that, by
exploiting the genomic and cellular simplicity afforded by invariantly developing Ciona embryos, one
can study these processes in vivo, with greater spatial and temporal resolution. With only 231 neurons
and a fully mapped “connectome”, the Ciona nervous system offers a singular opportunity to
understand cell behaviors and developmental trajectories in a chordate nervous system at single-cell
resolution. The central hypothesis will be tested by pursuing three specific aims: 1) Testing the role of
instrinsic and extrinsic TGFß pathway components in dynamically but invariantly polarizing neuronal
progenitors; 2) Investigating the causal links between regulation of effectors of receptor trafficking and
precisely timed inversion of intracellular polarity and axon outgrowth orientation. 3) Investigating the
role of collective epithelial sheet-like migration in precise positioning and morphogenesis of
differentiated neurons, and testing the involvement of tight junction proteins in regulating this unusual
mode of collective migration. These aims will be pursued using an innovative approach that combines
cell lineage-specific, CRISPR/Cas9-based somatic gene knockouts and live fluorescence microscopy.
The expected outcomes of the proposed work include identifying previously unrecognized functions for
conserved but poorly studied genes in neurodevelopment, and understanding how precise control
over neuronal subtype-specific polarized cell behaviors can be achieved through transcriptional
regulation of both intrinsic and extrinsic effector genes.