p0071, a member of the armadillo multigene family, is a constituent of sarcomeric I-bands in human skeletal muscle

p0071 is a member of the armadillo gene family that is expressed in a wide variety of mammalian tissues and cell types with a prominent cell-cell cont act association in epithelial cells. Here, we report the expression and loc alization patterns of p0071 in differentiating human skeletal muscle cells and in normal and diseased human skeletal muscle tissues. Northern blots re vealed expression of p0071 mRNA in adult skeletal muscle tissue. RT-PCR ana lysis and Western blotting experiments identified two differentially splice d isoforms of p0071. The balance between these isoforms shifted during in v itro differentiation of isolated muscle cells from predominant expression o f the short variant to a preponderance of the larger variant from day 6 onw ards. Immunolocalization studies in mature skeletal muscle tissue revealed that p0071 is a constituent of myofibrils with a distinct localization at t he level of sarcomeric N2-lines. During myofibrillogenesis, p0071 was not d etected in non-striated nascent myofibrils, but became apparent shortly aft er the development of compact Z-discs in early myotubes. Furthermore, we st udied the expression of p0071 in a wide variety of neuromuscular disorders by indirect immunofluorescence. Here, the myofibrillar staining of p0071 wa s preserved in all the disease entities included in our study. Our results provide the first evidence that a member of the armadillo multigene family is a constituent of the contractile apparatus in human skeletal muscle. The localization of p0071 at the level of I-bands and the timepoint of its int egration into developing myofibrils suggest a possible role in the organiza tion of thin filaments.