Fig. S8.

Model illustrating that HSPB7 represses excessive actin polymerization and formation of AABs. HSPB7 represses actin polymerization from barbed ends by binding actin monomers and limiting their availability to polymerize, thus maintaining normal Z-line width and proper thin filament length (WT). In HSPB7 KO mice, the inhibition of HSPB7 on actin polymerization from barbed ends is relieved, and as a result, actin filaments elongate from the barbed end, forming excessively wide Z structures extending across the sarcomere (light green portion). Some of the thin filaments extend beyond the actin-free H zone, overlapping with antiparallel actin filaments, and are cross-linked by α-actinin (an array of short red lines).