Abstract
Focal adhesions are multiprotein assemblages that link cells to the extracellular matrix. The transmembrane protein, integrin, is a key component of these structures. In vertebrate muscle, focal adhesion–like structures called costameres attach myofibrils at the periphery of muscle cells to the cell membrane. In Caenorhabditis elegans muscle, all the myofibrils are attached to the cell membrane at both dense bodies (Z-disks) and M-lines. Clustered at the base of dense bodies and M-lines, and associated with the cytoplasmic tail of β-integrin, is a complex of many proteins, including UNC-97 (vertebrate PINCH). Previously, we showed that UNC-97 interacts with UNC-98, a 37-kD protein, containing four C2H2 Zn fingers, that localizes to M-lines. We report that UNC-98 also interacts with the C-terminal portion of a myosin heavy chain. Multiple lines of evidence support a model in which UNC-98 links integrin-associated proteins to myosin in thick filaments at M-lines.
Highlights
In vertebrate striated muscle cells, the most peripherally located myofibrils are attached to the sarcolemma through costameres, structures compositionally and functionally similar to focal adhesions (Ervasti, 2003; Samarel, 2005)
To determine whether the N terminus of UNC-98 interacts with myosin heavy chain (MHC) A, prey plasmids were generated encoding the analogous region of MHC B, C, and D (Fig. 1 B)
The N terminus of UNC-98 interacts with the C terminus of MHC A but not with the equivalent regions of MHC B, C, and D in the yeast twohybrid system (Fig. 1, C and D). This result is consistent with the lack of expression of UNC-98 in the pharynx (Mercer et al, 2003), where MHC C and D are expressed
Summary
UNC-98 links an integrin-associated complex to thick filaments in Caenorhabditis elegans muscle. The transmembrane protein, integrin, is a key component of these structures. Focal adhesion–like structures called costameres attach myofibrils at the periphery of muscle cells to the cell membrane. In Caenorhabditis elegans muscle, all the myofibrils are attached to the cell membrane at both dense bodies (Z-disks) and M-lines. Clustered at the base of dense bodies and M-lines, and associated with the cytoplasmic tail of β-integrin, is a complex of many proteins, including UNC-97 (vertebrate PINCH). We showed that UNC-97 interacts with UNC-98, a 37-kD protein, containing four C2H2 Zn fingers, that localizes to M-lines. Multiple lines of evidence support a model in which UNC-98 links integrin-associated proteins to myosin in thick filaments at M-lines
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