Date of Award
Doctor of Philosophy (PhD)
Abstract of the DissertationStem Cell Models to Study the Regulation of Human Cortical Development and Its Disruption in Neurodevelopmental Disorders by Emily M. A. Lewis Doctor of Philosophy in Biology and Biomedical Sciences Developmental, Regenerative, and Stem Cell Biology Washington University in St. Louis, 2021 Professor Kristen L. Kroll, Chair
The cell state transitions that occur during complex processes, such as development of the human brain, require precisely controlled changes in gene expression. Major regulators of these developmental events include transcription factors (TFs), which bind the genome in a sequence-specific manner, as well as chromatin modifying proteins and complexes that alter TF access to the genome by modulating the DNA-histone protein structure of chromatin. Improper function of these classes of regulatory proteins as a result of genetic mutation represents a major contributor to neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASD), intellectual disability (ID), and epilepsy. It is therefore necessary to understand both how gene expression is regulated during normal brain development, and how impairment of this process contributes to NDDs.
Imbalances in excitatory and inhibitory neuronal activities in the cerebral cortex often occur when development of either cortical excitatory projection neurons (cExNs) or inhibitory interneurons (cINs) is disrupted. Thus, altered development of these neuronal cell types represents a major contributor to ASD, ID, and epilepsy etiology. Here, we applied human pluripotent stem cell (hPSC)-based differentiation methods to study the development of human cExNs and cINs in vitro. These approaches enable the study of aspects of human brain development which are otherwise intractable due to lack of access to and inability to experimentally manipulate human fetal material. In my graduate work, I first used these in vitro differentiation models to produce cExNs and cINs from induced PSCs (iPSCs) derived from several first-degree relatives in a multiplex ASD family. This work identified cellular and molecular correlates of ASD affectation, including abnormal expression of high-confidence ASD-associated genes in the most severely affected individuals. Next, I studied the role of the chromatin remodeler CHD2 in cIN development, which when mutated causes NDDs, including ASD and epilepsy. Here, I investigated its genomic targets during cIN differentiation, the histone modification state changes associated with these CHD2 binding events, and the consequences of CHD2 haploinsufficiency. This work suggests that CHD2 is important both for maintaining expression of genes required to modulate the transitions from pluripotency through neurectoderm induction and for progenitor specification and proliferation, as well as playing a later role in activation of genes required for hcIN differentiation and maturation. Finally, in addition to studying gene regulation of cortical development, I also studied this process in a different context, the developing mouse limb. Conditional loss of Geminin (Gmnn), which encodes a regulatory nucleoprotein, resulted in improper spatial and temporal expression of Hox genes during limb bud patterning, causing dramatic later defects in limb patterning. Taken together, this work advances our understanding of how gene regulation occurs during multiple developmental processes and how its disruption can contribute to developmental disorders.
Chair and Committee
Kristen L. Kroll
Shiming Chen, Harrison W. Gabel, Charles K. Kaufman, Andrew S. Yoo,
Lewis, Emily Megan Alexandra, "Stem Cell Models to Study the Regulation of Human Cortical Development and Its Disruption in Neurodevelopmental Disorders" (2021). Arts & Sciences Electronic Theses and Dissertations. 2436.