Desmin organization during the differentiation of the dorsal myotome in Xenopus laevis.

The reorganization of desmin-type intermediate filaments during muscle differentiation has been studied primarily in cultured cell systems. Here we describe the process of desmin reorganization during the differentiation of the dorsal myotomal muscle of the clawed frog Xenopus laevis. This muscle differs from those described previously primarily in that the desmin system forms de novo, i.e., without the presence of a pre-existing vimentin filament system. The most striking observation is that prior to myotomal segmentation and rotation desmin is concentrated at the medial and lateral tips of the myocytes. It remains concentrated in these regions following somite rotation and is located primarily to the intersomite junctions as late as the stage 33-35 tadpole. As the muscle matures (stage 30 and later) desmin becomes increasingly associated with the sarcolemma and with the Z-discs. The concentration of desmin at the nascent intersomite junction suggests that desmin is involved in coupling somites to one another in the early Xenopus embryo.