Development and analysis of CTG repeat expansion cell lines to understand molecular events in myotonic dystrophy type 1

Malik, Naveed Altaf (2018) Development and analysis of CTG repeat expansion cell lines to understand molecular events in myotonic dystrophy type 1. PhD thesis, University of Nottingham.

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Abstract

Myotonic dystrophy type 1 (DM1) is a dominant human neuromuscular disorder caused by a CTG repeat expansion at the 3’ end of the DMPK gene. Pathogenesis of DM1 is linked to a toxic gain of function due to mutant RNA and is manifested by nuclear retention of expanded CUG repeats and aberrant splicing. The development of an inducible model for DM1 with uninterrupted CTG repeats could help us to better understand early pathogenic changes in DM1 due to CUG repeat expansion.

In the first part of this thesis, I report an inducible C2C12 mouse myoblast cell line in which the pTetOne inducible system was used to express 174 CTG repeats. This resulted in the production of RNA foci in 26% of cells. Efforts to make larger un-interrupted CTG repeats were unsuccessful due to their instability in the E.coli plasmid. In the second part of the thesis, I used the CRISPR/Cas9-induced genome-editing technique to knock-in an inducible promoter into the endogenous DMPK gene in a DM1 fibroblast cell line. For this, I employed two different CRISPR/Cas9 based strategies which exploit homology-directed repair (HDR) and non-homologous end joining (NHEJ). Our results suggest that CRISPR/Cas9 induced knock-in is enabled by non-homologous end joining more efficiently as compared to homology-directed repair.

In the last part of the thesis, TruSeq RNA Sequencing was used to quantify the number of mutant DMPK transcripts and other molecular markers of DM1 pathogenesis that could be a valuable tool for the evaluation of the efficacy of therapeutic compounds. The sequencing results reveal the significant low abundance of mutant DMPK transcripts in the cytoplasmic fraction of DM1 lines and confirm the previously reported nuclear retention of mutant DMPK transcripts. We identify six potential genes which are dysregulated in DM1 fibroblasts and the absolute quantification of mutant DMPK transcripts along with these six reported dysregulated genes can be suitable biomarkers for disease severity and therapeutic response in DM1 fibroblasts. Additionally, these assays could be further refined to provide valuable tools to assess therapeutic compounds.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Brook, David
Hayes, Chris
Subjects: Q Science > QH Natural history. Biology > QH426 Genetics
Q Science > QP Physiology > QP351 Neurophysiology and neuropsychology
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID: 53025
Depositing User: Malik, Naveed
Date Deposited: 13 Dec 2018 04:40
Last Modified: 08 Feb 2019 08:46
URI: http://eprints.nottingham.ac.uk/id/eprint/53025

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