Molecular pathogenesis of select mutations in DMD and SEPN1

Sophisticated sequencing techniques have led to the identification of a vast array of pathogenic mutations, most of which are associated with predictable phenotypes. A small fraction of these mutations gives rise to discordant phenotypes and often provides crucial insights about the affected gene and its protein product. Such a subset of reported point mutations in the DMD and SEPN1 gene forms the basis of this dissertation.;Another set of single missense mutations defined in the cysteine-rich region of dystrophin, lies at the opposite end of spectrum. Here in spite of the presence of properly localized dystrophin the patients present with severe dystrophic phenotypes. Studies described here suggest that the mutant dystrophin still retains the ability to bind its known interacting partners beta-dystroglycan and calmodulin. This highlights the functional importance of the ZZ domain and suggests that the cysteine-rich region of dystrophin may possess unanticipated physiologic functions and that these are possibly mediated via interaction with other unknown proteins.;Mutations in SPEN1 gene result in a spectrum of clinically related early onset myopathies. In a section of the dissertation we illustrate a novel molecular mechanism by which single missense mutations in the SEPN1 gene affects the translation of its protein product selenoprotein N (SelN). Our data show a point mutation which weakens the secondary structure of an RNA structural element, the Selenocysteine Redefinition Element (SRE) in the SEPN1 mRNA affects efficiency of selenocysteine incorportation in SelN and potentially contributes to the pathology.;In this dissertation the dissection of specific pathogenic mutations in two inherited muscle disorders helps to elucidate key aspects of both translation and function of the affected proteins. A deeper understanding of these underlying mechanisms could aid in the design of effective therapeutic strategies.;Mutations in DMD gene cause two allelic disorders associated with progressive degeneration of the skeletal muscle; the more severe Duchenne muscular dystrophy (DMD) and the milder Becker muscular dystrophy (BMD). Nonsense mutations have been identified within the first exon of the DMD gene which surprisingly lead to very mild BMD phenotype. A section of this dissertation delineates the molecular mechanism responsible for the amelioration of disease severity to be internal initiation of translation at two proximate AUG codons within exon 6 of DMD gene. Initial studies suggest an Internal Ribosomal Entry Site (IRES) in the DMD coding sequence orchestrates this initiation.