Characterization of mouse myotilin and its promoter

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Abstract

Myotilin is a sarcomeric protein mutated in two forms of muscle disease, limb-girdle muscular dystrophy type 1A and myofibrillar myopathy. Myotilin is expressed late during human myofibrillogenesis and localizes to Z-discs in mature sarcomere. It interacts with α-actinin, actin, and filamin C, and has strong F-actin-bundling activity. These features suggest an important role for myotilin in sarcomere organization. In our effort towards the construction of a genetic model for myotilin-related muscle disorders, we have cloned mouse myotilin, including its promoter region, and studied the expression in various tissues. Mouse myotilin is 90% identical with the human orthologue. Northern blot analysis revealed strong mRNA transcripts in skeletal and cardiac muscle, and weak expression in liver and lung tissue. Western blot and RT-PCR analysis showed the presence of one major product in mouse tissues. Analysis of the 5′-flanking region revealed a number of putative regulatory elements that drive expression in differentiating myoblasts. Finally, endogenous myotilin is induced at later stages of Z-disc assembly in C2C12 cells indicating conservation between mouse and human promoter region.

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Materials and methods

cDNA cloning, gene structure, and probes. A cDNA library (Uni-ZAP XR library, Stratagene) derived from mouse skeletal muscle was screened using human full-length myotilin cDNA as a probe. Positive clones were analyzed by PCR with myotilin-specific primers, and a partial cDNA clone was identified and used as a probe for subsequent screening. Full-length mouse myotilin cDNAs were then isolated and sequenced by ABI 310 Genetic Analyzer (Perkin-Elmer). Sequence alignments were done with the

Molecular cloning of mouse myotilin

Full-length myotilin cDNA (isoform I, GenBank Accession No. AF230979) was identified from a mouse skeletal muscle library using human cDNA and a partial mouse cDNA as probes. It contains a 1491 bp open reading frame (ORF) encoding for a 496 amino acid polypeptide (Fig. 1A) of a predicted molecular mass of approximately 55 kDa. Another identified myotilin sequence (isoform II) had a shorter 5′-untranslated sequence due to alternative splicing at a cryptic splice site on the second exon, thus

Discussion

We present here the cloning of mouse myotilin and the characterization of its expression pattern in adult tissues. Both the general genomic structure and the coding sequence are highly conserved between mouse and human myotilin. The sequence identity is lower in untranslated regions and drops considerably within introns. At the amino acid level (especially within the Ig-like domains and the serine repeats), the sequence conservation is even higher, well above the average 85% identity between

Acknowledgments

We are grateful to Tuula Halmesvaara for excellent technical assistance, Dr. Mikko Rönty for help in staining of C2C12 cells, Dr. Sigfried Labeit for the titin probe, and Dr. Jaques Beckmann for helpful discussion. This work was supported by the Sigrid Juselius Foundation and the Academy of Finland.

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  • Cited by (0)

    1

    Present address: University of Milan-Bicocca, Milan, Italy.

    2

    Present address: Max Delbrück Center for Molecular Medicine, Berlin, Germany.

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