Project Abstract

The candidate for this Wellstone Administrative Supplemental Research Fellowship, Jill W. Miller, MD, PhD, will undertake collaborative studies of disease pathogenesis in myotonic dystrophy type 1 (DM1). The proposed program of research and mentoring will take place at Wellstone MDCRCs in Rochester , New York and in Seattle , Washington . During her graduate studies, Dr Miller was engaged in research on the role of RNA-protein interactions in DM1 pathogenesis. She identified muscleblind proteins as the major poly(CUG) binding proteins in the mammalian nucleus. During her Fellowship, Dr Miller will continue to focus on the hypothesis that pathogenesis of DM1 involves the accumulation in nuclear foci of mutant mRNA that contains an expanded CUG repeat. Recent evidence indicates that specific aspects of the DM1 phenotype can be attributed to sequestration of muscleblind 1 (MBNL1) in nuclear foci, which results in misregulated alternative splicing for a select group of pre-mRNAs. A second member of the muscleblind family of splicing factors, MBNL2, is also sequestered in nuclear foci in DM1 myonuclei, but less is known about its normal function or the consequences of its redistribution. To address this question, the applicant has derived mice with a gene-trap (GT) disruption of the Mbnl2 gene. mRNA and protein studies will be carried out to confirm that Mbnl2 function is mainly or entirely eliminated in mice homozygous for the Mbnl2-GT allele. The effects of Mbnl2 deficiency on development, structure, excitability, and RNA processing in skeletal muscle will be determined in Mbnl2-GT homozygous mice. These results will lay the groundwork for future studies to compare the effects Mbnl1 and Mbnl2 deficiency, singly and in combination. A second Aim is to develop a cell culture system to determine how the presence of a CUG expansion within the 3' untranslated region of an mRNA affects its cellular distribution and decay. The goal of this Aim is to develop a system to identify the rate-limiting steps and genes responsible for degradation of this toxic mRNA. Together, this proposal represents a program of research and training that is focused on aspects of DM1 pathogenesis that are viable targets for therapeutic intervention: the interaction of CUG expansion RNA with muscleblind proteins, and the cellular pathways responsible for degradation of CUG expansion RNA.