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Lens growth and development is a life-long process in which epithelial cells from the perimeter of the lens migrate towards the centre of the lens and follow a dynamic programme of differentiation and structured DNA and organelle degradation resulting in the optical clarity of the lens. Myotonic dystrophy type 1 (DM1) is a genetic disease resulting in multiple symptoms including skeletal muscle wasting, cardiac conduction defects, myotonia and endocrine system malfunction. DM1 is caused by an expanded CTG repeat in the 3' untranslated region (UTR) of the myotonic dystrophy protein kinase (DMPK) gene. Mutant DMPK RNA has been demonstrated to form abnormal foci within the cell nucleus in muscle cells from DM1 patients. The link between these foci and the multiple symptoms of DM1 is not fully understood. The alternative pre-mRNA splicing factor muscle blind-like 1 (MBNL1) is found in the foci and sequestration of MBNL1 is a leading hypothesis for pathogenesis. Results shown in this thesis demonstrate that only a small percentage of nuclear MBNL1 is sequestrated into foci. Furthermore MBNL1 is shown to co-localise with splicing speckles in a transcriptionally dependent manner. Interestingly eye lens histological samples suggest a change in MBNL1 distribution during lens growth. The data presented in this thesis shows a strong relationship between MBNL1 and CUGexp pre-mRNA foci and presents data which highlights the sensitivity of lens epitheial cells to changes in MBNL1.