The role of the FACT complex in differentiation of multipotent stem cells

by Tareq Hossan
Doctoral thesis
Date of Examination:2016-05-23
Date of issue:2017-04-27
Advisor:Prof. Dr. Steven Johnsen
Referee:Prof. Dr. Ernst A. Wimmer
Referee:Prof. Dr. Heinz Neumann
Persistent Address: http://dx.doi.org/10.53846/goediss-6261

 

 

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Abstract

English

Cellular differentiation is accompanied by dramatic changes in chromatin structure which are associated with the activation of lineage-specific transcriptional programs. Facilitates Chromatin Transcription (FACT) is a histone chaperone complex which is important for chromatin-associated processes such as transcription, DNA replication and DNA repair. However, the role of FACT during differentiation of undifferentiated or stem-cell like cells has not yet been elucidated. We investigated the role of the FACT component Structure Specific Recognition Protein 1 (SSRP1) in adipocyte and osteoblast differentiation. Depletion of SSRP1 in human mesenchymal stem cells (hMSC) elicited lineage-specific effects where the adipocyte-specific genes PPARG, RASD1 and PDK4 were significantly increased while markers of osteoblast differentiation markedly decreased. Consistently, Oil Red O staining was increased during adipocyte differentiation while alkaline phosphatase staining was decreased in osteoblast differentiation following knockdown of SSRP1. Osteoblast differentiation plays a pivotal role in maintenance of bone homeostasis important for different bone-associated diseases including age-related bone loss. Thus this study was further focused on the molecular regulation of SSRP1-mediated effects on osteoblast differentiation. Transcriptome-wide RNA-seq revealed a specific enrichment of down-regulation of the canonical Wnt signaling pathway following SSRP1 depletion in osteoblasts. Furthermore a number of biological processes important for osteoblast differentiation including glycosylation, cell-cell contact, adhesion, extra cellular matrix, ossification, osteoblast differentiation, bone and skeletal development were affected by SSRP1 knockdown. In addition a significant nuclear co-localization of SSRP1 and β-catenin was observed where depletion of SSRP1 diminished accumulation of active β-catenin in the nucleus. Together, our data suggest a previously unknown specific role for SSRP1 in promoting the activation of canonical Wnt signaling during lineage-specific differentiation.
Keywords: Histone chaperone, Structure specific recognition protein, Osteoblast differentiation, Wnt signaling
 
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