Analysis of Ret and β-catenin

: transcriptional targets of the facioscapulohumeral muscular dystrophy (FSHD) candidate gene DUX4

Abstract

Skeletal muscle maintenance and repair is performed by resident stem cells, called satellite cells. The muscular dystrophies are a group of disorders which are characterised by progressive muscle weakness and wasting. Therefore, this satellite cell-mediated repair process is likely to be compromised, directly contributing to disease progression. Facioscapulohumeral muscular dystrophy (FSHD) is the third commonest muscular dystrophy, caused by contraction in the number of repeat units (D4Z4) on 4q35. A D4Z4 contraction on the chromosomal haplotype 4qA leads to the production of double homeobox protein (DUX4) in muscle cells. DUX4 is pro-apoptotic and perturbs myogenic differentiation, and is thought to be the primary cause of FSHD pathology.

A microarray was performed on murine satellite cells expressing retroviral-mediated DUX4 expression to understand the signalling pathways dysregulated by this transcription factor. In this thesis, several candidate genes altered by DUX4 were examined in satellite cells, with Ret and β-catenin being examined in detail in this thesis.

Ret and its GFRα co-receptors are dynamically expressed in satellite cells throughout myogenic differentiation. Manipulation using retroviral-mediated expression and siRNA-knockdown show that Ret acts to regulate satellite cell proliferation. Several ‘rescue’ experiments were then performed to block RET and β-catenin signalling in DUX4-expressing myoblasts, in order to determine whether these DUX4-activated pathways are involved in pathogenesis. Although manipulation of β-catenin levels failed to ameliorate the pathogenic phenotype, DUX4-mediated RET signalling is shown to contribute to pathology by reducing myogenic differentiation. Importantly, this thesis contains evidence that a clinically-approved RET-inhibitor improves the myogenic capacity of DUX4-expressing satellite cells.

This work will both help elucidate how DUX4 expression leads to cellular pathology, and provide an insight into novel mediators of satellite cell function.

Date of Award	1 Feb 2015
Original language	English
Awarding Institution	King's College London
Supervisor	Peter Zammit (Supervisor)