UC Irvine

In embryonic development, tissues arise from multipotent progenitor populations and undergo lineage specification and terminal differentiation. Two examples of this are the neural crest (NC) and the multiple progenitor cells of the tailbud. The NC is a multipotent highly migratory cell type that gives rise to numerous tissues and cell types in the adult animal, including pigmentation, cartilage and bone, neurons and glia, and many others. Much is known about the mechanisms driving NC induction and migration, but how lineage specification and migration are coordinated is still not well-understood. To address outstanding questions in NC development, we took a multifaceted approach, employing both traditional functional characterization of a novel Wnt regulator and data-driven single-cell and bulk transcriptomics.

Here, I show that Lmo7a regulates both migration and specification of glial and pigment lineages through interactions with focal adhesions (FAs) and canonical Wnt signaling. Lmo7a is expressed in premigratory NC cell, and its loss results in large midline aggregates of NC cells that go on to express markers of pigment and glial lineages. These cells also show abnormally high levels of canonical Wnt signaling. I show that Lmo7a is required for proper formation of FAs, suggesting a novel connection between cell adhesion and lineage specification in the NC through canonical Wnt signaling.

I also build a single-cell RNA-seq timeline of cranial NC development to investigate lineage decisions. I identify the precise timing of pigment, skeletal, and neural/glial lineage specification and identify several novel markers of each. Further, using combinatorial analysis of bulk and single-cell RNA-seq data, I computationally model the Wnt signaling dynamics that correspond to lineage specification. I identify a putative Wnt regulatory gene atp6ap2 which encodes the (Pro)renin receptor ((P)RR) protein as a potential regulator of pigment development. Using CRISPR-Cas9 genome editing, I verify a role for ((P)RR) in pigment maturation potentially through canonical Wnt signaling.

I also investigate lineage relationships in the tailbud by constructing a comprehensive single-cell transcriptome map of all cells in the tailbud. I uncover evidence for a novel connection between neuromesodermal progenitors and both vascular endothelium and hematopoiesis. I also show that cell cycle arrest is indicative of a notochord fate in midline progenitor cells. In this thesis, I provide novel insights into lineage specification in the NC and tailbud.