Fig. 9. The dominant sub-cellular localization of nesprin-2 isoforms changes during differentiation of C2C12 myoblasts to myotubes. (A) In myoblasts (top panel) the predominant N2 staining was nuclear, in a punctate pattern at the NE with only very weak cytoplasmic staining. In myotubes (lower panel) N2 recognised cytoplasmic structures of the muscle sarcomere organised in a striated pattern (arrows). Bottom inset: myosin staining to show differentiation and myofibre formation (small arrow) with N2 located between myosin positive bands. Top inset: the change in nuclear distribution of N2 in myotubes into a less punctate pattern (arrow). (B) Western blot analysis using the nesprin-2 N2 antibody and sub-cellular fractions of C2C12 myoblasts and myotubes demonstrated a shift in nesprin-2 isoform patterns in the cytoplasm and nucleus. The larger cytoplasmic isoforms were more highly expressed in myotubes with a reduction in smaller cytoplasmic isoforms and there was higher expression of two small nuclear isoforms in myotubes than in myoblasts.