Tissue-specific Isoforms of Chicken Myomesin Are Generated by Alternative Splicing

Abstract

Myomesin is a high molecular weight protein that is present in the M-band of all fiber types of cross-striated skeletal muscle and heart. We have isolated two cDNAs encoding tissue-specific isoforms of chicken myomesin with calculated molecular masses of 174 kDa in skeletal muscle and 182 kDa in heart. Distinct sequences are found at the 3-end of the two cDNAs, giving rise to different C-terminal domains. Partial analysis of the gene structure has shown that in chicken, both isoforms are generated by alternative splicing of a composite exon. Amino acid sequences show that the main body of myomesin consists of five fibronectin type III (class I motifs) and seven immunoglobulin-like domains (class II motifs). An identical structure was found in M-protein and human 190K protein (the human counterpart of chicken myomesin), and a comparable domain arrangement occurs in the M-band-associated protein skelemin. We postulate that myomesin, M-protein, and skelemin belong to the same subfamily of high molecular weight M-band-associated proteins of the immunoglobulin superfamily and that they probably have the same ancestor in evolution.

A Novel Marker for Vertebrate Embryonic Heart, the EH-myomesin Isoform

“…Subsequently, two transcripts of different sizes were detected in chicken heart and skeletal muscle (8). The two isoforms differ only at their respective C termini, whereas the major part of the protein, which consists of a unique head domain followed by a conserved pattern of immunoglobulin-like and fibronectin type III domains, is identical.…”

“…It has recently been demonstrated that myomesin, an integral component of the M-band, is also expressed in several isoforms (8,12). Myomesin is present in all kinds of vertebrate striated muscle and is thought to play an important role in the integration of thick filaments with titin, a hypothesis based on its ability to bind both proteins in vitro (13).…”

The M-band: an elastic web that crosslinks thick filaments in the center of the sarcomere

“…Myomesin can be alternatively spliced at the C-terminus, a variant being found in avian heart [27], and between domains My6 and My7, leading to the insertion of w100 amino acids (aa) (Figure 2). The resulting protein was initially described as skelemin [28], but later was proven to be a myomesin isoform [29] and was named EH-myomesin because it is the major isoform in the embryonic heart of all higher vertebrates [25].…”

A influência do hormônio tireoideano nas proteínas estruturais da banda M no coração e no músculo esquelético de ratos.

“…Tem sido sugerido que a banda M apresenta um importante papel organizacional durante a miofibrilogênese, quando os filamentos grossos nascentes têm de montar e estar alinhados numa treliça regular hexagonal (Ehler et al, 1999;Wang et al, 1998;Yang et al, 2000). A miomesina e a proteína M, proteínas intimamente relacionadas, pertencem à família das proteínas imunoglobulinas, a qual os membros consistem de um domínio N-terminal único seguido de domínios de seqüência conservada semelhantes à imunoglobulina (Ig) e fibronectina tipo III (Bantle et al, 1996;Vinkemeier et al, 1993). Apesar dessa forte similaridade, essas duas proteínas exibem diferentes padrões de expressão.…”

“…A miomesina e a proteína M, proteínas intimamente relacionadas, pertencem à família das proteínas imunoglobulinas, a qual os membros consistem de um domínio N-terminal único seguido de domínios de seqüência conservada semelhantes à imunoglobulina (Ig) e fibronectina tipo III (Bantle et al, 1996;Vinkemeier et al, 1993). Apesar dessa forte similaridade, essas duas proteínas exibem diferentes padrões de expressão.…”