All ETDs from UAB

Advisory Committee Chair

Hengbin Wang

Advisory Committee Members

Chenbei Chang

Louise Chow

Christopher A Klug

Tim M Townes

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

In eukaryotic cells, genomic DNA is packaged into a chromatin structure by association with histone and non-histone proteins. Posttranslational modifications of histones play important roles in the regulation of chromatin structure and function. Ubiquitination of histone H2A (ubH2A) represents a predominate modification, occurring on ~10% of total cellular H2A. While H2A ubiquitination is primarily conferred by Polycomb Repressive Complex 1 (PRC1), H2A deubiquitination has been attributed to multiple H2A deubiquitinases. Our laboratory previously reported the purification and functional characterization of a H2A-specific deubiquitinase, USP16 (initially named as Ubp-M) in human cells. However, whether USP16 represents a general and important regulator for H2A deubiquitination and the functional significance of USP16-mediated H2A deubiquitination during development remain largely elusive. To study the function of USP16 in development, we generated Usp16 complete and conditional mouse models. Previously PRC1 and ubH2A have been shown to contribute to embryonic stem cell (ESC) pluripotency by repressing lineage-specific gene expression. However, whether active deubiquitination co-regulates ubH2A levels in ESCs and during differentiation is not known. We discovered here that Usp16 regulates H2A deubiquitination and gene expression in ESCs, and importantly, is required for ESC differentiation. Usp16 knockout is embryonic lethal in mice, but does not affect ESC viability or identity. Usp16 binds to the promoter regions of a large number of genes in ESCs, and Usp16 binding is inversely correlated with ubH2A levels, and positively correlated with gene expression levels. Intriguingly, Usp16-/- ESCs fail to differentiate due to ubH2A-mediated repression of lineage-specific genes. Finally, Usp16, but not a catalytically inactive mutant, rescues the differentiation defects of Usp16-/- ESCs. Therefore, this study identifies Usp16 and H2A deubiquitination as critical regulators of ESC gene expression and differentiation. Our studies on USP16 complete and conditional knockout mouse models reveal USP16 as an important, probably the major, regulator for H2A deubiquitination in vivo. Our studies further demonstrate that USP16 and its mediated H2A deubiquitination play critical roles in mouse ESC lineage commitment.

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