Dissecting the Role of TONSOKU in the Regulation of Genome Stability
Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Molecular, Cellular, and Developmental Biology
First Advisor
Jacob, Yannick
Abstract
DNA is packaged around nucleosomes formed by two copies of core histones, H2A, H2B, H3, and H4. The core histones not only create a structural backbone of chromatin but are also crucial in regulating DNA replication, DNA repair, and transcription. In plants, the H3 family contains two major isoforms, H3.1 and H3.3. H3.1 is characterized by an alanine residue at position 31 (A31) and this position is occupied by a threonine residue in the H3.3 variant. It was hypothesized that epigenetic information is provided by a unique pattern of H3 variants that are in turn recognized by specific reader proteins. However, the current body of evidence in support of this hypothesis remains limited. In plants, the histone-lysine N-methyltransferases ATXR5 and ATXR6 catalyze the mono-methylation of K27 specifically on H3.1 (H3.1K27me1), and loss of H3.1K27me1 triggers genomic instability. Apart from an obvious link to heterochromatin, the precise relationship between H3.1K27me1 and genome stability has remained unclear. Through genetic screening, chemical biology, and structural biology approaches, I found that the tetratricopeptide repeat (TPR) domain of the TONSOKU (TSK) protein is a reader that can recognize the distinctive A31 residue of H3.1 in Arabidopsis thaliana. Structural analyses showed that A31 is essential for binding TSK and its ortholog in animals. The A. thaliana tsk mutants showed high sensitivity to DNA-damaging agents and genetic interaction with mutants involved in genome stability. I, therefore, suspected that TSK binding to H3.1 would be regulated by histone modifications and found that H3.1K27me1 limits TSK binding to H3.1 nucleosomes. I propose that, in the absence of H3.1K27me1, TSK is recruited to regions away from replication forks, thereby causing genome instability. In brief, this study identifies the first replicative H3 reader and lends credence to the H3 variant code hypothesis, expanding the idea that histone variants provide the foundation of chromatin functional organization. The second aim of this study was to investigate the potential involvement of the H3.1-TSK pathway in the manifestation of genome instability phenotypes beyond those associated with atxr5/6. I discovered that H3.1-TSK is the primary driver of H3K27M genome instability and demonstrated that this phenotype can be mitigated through the loss of TSK function. Given that H3K27M is the dominant oncogene in GBM cancers, my findings have the potential to offer a novel therapeutic avenue for future treatment.
Recommended Citation
Huang, YiChun, "Dissecting the Role of TONSOKU in the Regulation of Genome Stability" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1042.
https://elischolar.library.yale.edu/gsas_dissertations/1042
