ORCID
https://orcid.org/0000-0002-8874-0673
Date of Award
12-22-2023
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
The development of the nervous system relies on precise control of protein ubiquitination and degradation. Consequently, imbalance in the ubiquitin signaling network is believed to have significant implications for neurological disorders. Recent research has not only detailed the various functions of different ubiquitin ligases in neural development, but has also disclosed the role of deubiquitinating enzyme as an additional regulatory dimension in the ubiquitin signaling network. Specifically, deletion or mutation of the deubiquitinating enzyme USP7 causes the Hao-Fountain syndrome, characterized by developmental delay, intellectual disability, autism, and aggressive behavior. Although USP7 has been studied in proliferating cells in the context of cancer biology, the roles and mechanisms of USP7 in post-mitotic neurons have remained largely unknown. In this dissertation, I investigated the effect of conditionally deleting USP7 in excitatory glutamatergic neurons in the mouse forebrain. This USP7 deletion resulted in diverse phenotypes in adult mice including sensorimotor deficits, learning and memory impairment, and aggressive behavior. In developmental analyses of the cerebral cortex, USP7 deletion induced neuronal apoptosis perinatally, which was rescued by loss of the tumor suppressor protein p53, an established downstream mediator of USP7 signaling. Interestingly, most of the behavior abnormalities in USP7 conditional mice were not affected by the absence of p53. Furthermore, I found that USP7 deletion in the brain also reduced synaptic proteins and dendritic spine density in excitatory pyramidal neuron, independent of p53. Through a combination of interaction and TMT-proteomics as well as ubiquitin biochemistry assays, I next examined the mechanisms of USP7 in post-mitotic neurons. Biochemical analyses of the USP7 interactome in neurons uncovered the SWI/SNF chromatin remodeling and spliceosomal complexes, implicating USP7 in fundamental aspects of chromatin and gene regulation in neurons. In quantitative TMT-proteomic and biochemical ubiquitin analyses, I identified the RNA splicing factor Ppil4 as a novel substrate of USP7. Knockdown of Ppil4 in cortical neurons impairs dendritic spine morphogenesis, phenocopying the effect of conditional knockout of USP7 on dendritic spine morphogenesis. Collectively, this work reveal both p53-dependent and p53-independent function of USP7 in excitatory neurons, and defined a novel USP7-Ppil4 ubiquitin signaling link that regulates neuronal connectivity in the developing brain, with implications for our understanding of the pathogenesis of the Hao-Fountain syndrome.
Language
English (en)
Chair and Committee
Albert Kim
Committee Members
Azad Bonni
Recommended Citation
Chen, Hao, "Investigation of the Deubiquitinating Enzyme USP7 in the Brain" (2023). Arts & Sciences Electronic Theses and Dissertations. 3222.
https://openscholarship.wustl.edu/art_sci_etds/3222