Differences in the distribution of synemin, paranemin, and plectin in skeletal muscles of wild-type and desmin knock-out mice

Mice lacking the gene encoding fur the intermediate filament protein desmin have a surprisingly normal myofibrillar organization in skeletal muscle fi bers, although myopathy develops in highly used muscles. In the present stu dy we examined how synemin, paranemin, and plectin, three key cytoskeletal proteins related to desmin, are organized in normal and desmin knock-out (K /O) mice. We show that in wild-type mice, synemin, paranemin, and plectin w ere colocalized with desmin in Z-disc-associated striations and at the sarc olemma. All three proteins were also present at the myotendinous junctions and in the postsynaptic area of motor end-plates. In the desmin K/O mice th e distribution of plectin was unaffected, whereas synemin and paranemin wer e partly affected. The Z-disc-associated striations were in general no long er present in between the myofibrils. In contrast, at the myotendinous and neuromuscular junctions synemin and paranemin were still present. Our study shows that plectin differs from synemin and paranemin in its binding prope rties to the myofibrillar Z-discs and that the cytoskeleton in junctional a reas is particularly complex in its organization.