Mitochondrial expression of a short dystrophin-like product with molecular weight of 71 kDa.

In the brain, Dp71 is the most abundant protein product of the DMD gene and by alternative splicing of exon 78 two isoforms can be expressed, Dp71d and Dp71f. To explore the subcellular distribution of these Dp71 isoforms, specific monoclonal antibodies were used. Dp71d (with exon 78) was found in microsomes, while Dp71f (without exon 78) was detected in mitochondria. To determine the alterations which the absence of dystrophin proteins induces, we compared the expression of Dp71d in microsomes and Dp71f in mitochondria from mdx and mdx(3CV) mice. Dp71d in microsomes of mdx was similar to that of wild-type mice and, as expected, in mdx(3CV) this protein was undetectable. However, in mitochondria from mdx(3CV), Dp71f was overexpressed in comparison to mitochondria from mdx mice. Because in mdx(3CV) mice all the dystrophin proteins are mutated or diminished, we concluded that the protein detected in mitochondria is not a Dp71f but a novel product named Dp71f-like protein.