FIGURE 9:

FMNL1 and FMNL2 are required for repair of damaged myofibrils. (A) Time course of Z-band repair after injury. To induce myofibril damage, neonatal mouse cardiomyocytes were grown in culture for 48 h, then treated with LatA for 24 h and allowed to recover for 24 or 48 h. α-Actinin banding patterns returned to normal by 24 h of recovery from LatA. (B) Formin requirement in myofibril repair. LatA was used to induce myofibril damage in neonatal primary culture cardiomyocytes in which either Daam1, mDia2, Fmnl1, or Fmnl2 was silenced using siRNA. Images of the injured siRNA cells after 48 h of recovery from LatA treatment. Note that Fmnl1 and Fmnl2 siRNA cells fail to reestablish organized sarcomeric structures, even after 48 h of recovery, whereas Daam1 and mDia2 siRNA cells recovered normally within 24 h. (C) Localization of FMNL1 or FMNL2 (green) and α-actinin (red) in control (untreated) cells, in cells treated with LatA for 24 h, and in cells allowed to recover for 24 or 48 h after LatA treatment. Merged images are shown (individual images are shown in Supplemental Figure S4). Scale bars, 10 μm.