The Role of CHD1 during Mesenchymal Stem Cell Differentiation

by Simon Baumgart
Doctoral thesis
Date of Examination:2016-02-22
Date of issue:2017-01-23
Advisor:Prof. Dr. Steven A. Johnsen
Referee:Prof. Dr. Steven A. Johnsen
Referee:Prof. Dr. Heidi Hahn
Persistent Address: http://dx.doi.org/10.53846/goediss-5923

 

 

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Abstract

English

Nucleosome remodeling, histone modifications and exchange of histone variants are interconnected mechanisms involved in regulation of gene transcription. Nucleosomes can act as strong barriers and are remodeled during RNA-Pol II-mediated transcription elongation. Remodeling of nucleosomes is tightly regulated in particular during activation and inhibition of cellular differentiation. The nucleosome remodeler CHD1 is a transcriptional co-activator involved in RNA-Pol II processivity downstream of the transcriptional start site (TSS). In this study we hypothesized that CHD1 not only acts as a general co-activator of transcription but can also regulate gene specific expression. Therefore, we investigated the role of CHD1 on gene regulation after induction of adipocyte and osteoblast differentiation. Genome-wide binding analysis of CHD1 during differentiation revealed high occupancy at TSS-regions of adipocyte and osteoblast activated genes. Further we observed direct regulation of these activated genes by enriched CHD1 binding around TSS. Concordantly, CHD1 was required for ectopic bone formation in mice. Besides these biological aspects it could here be shown that global RNA-Pol II stalling downstream of TSS was caused by CHD1 depletion. This highlights its genomic role for efficient early RNA-Pol II-mediated transcription elongation. A group of highly activated genes during osteoblast differentiation was found to be repressed by significantly increased RNA-Pol II stalling ratios in parallel with decreased CHD1 protein levels. Interestingly, high steady-state levels of the histone variant H2A.Z at the TSS-region were revealed to be dependent on CHD1. This presumably increases the nucleosome stability and thus cause the observed global RNA-Pol II stalling. Summarized, CHD1 was shown to be necessary for a genome-wide, efficient RNA-Pol II-mediated early transcription elongation, probably achieved by decreasing the nucleosome barrier at the TSS-region. In particular, CHD1 was required for the activation of a group of genes involved in osteoblast differentiation. This implies a function for CHD1 as a regulatory protein in cell differentiation. Further we propose that CHD1 should be considered in quality control of MSC in skeletal stem cell therapies.
Keywords: Mesenchymal stem cell differentiation; Transcriptional Regulation; Epigenetics
 
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