Figure. Sarcomere Assembly in a Zebrafish Heart.

A, Immunostaining of a zebrafish heart using anti-Actinin antibody on embryos at the 18 somite (S), 24 S, 26 S, and 48 hours postfertilization (hpf) stages, respectively. Scale bar indicates 20 μm. Arrows and arrowheads indicate Z-bodies and Z-discs at different developmental stages. Images adapted from (Huang, Zhang et al. 2009). B, Schematic of the 6 stages of sarcomere assembly in the zebrafish heart. Stage 1, around 10–12 S, the actin filament is assembled along the cell membrane while the myosin filaments independently form rodlet structures. Stage 2, around 18 S, actin filaments and thick filaments are integrated where Actinin is randomly located as irregular spaced dots. Stage 3, around 24 S, the sarcomere becomes more organized, with consistent shorter length. Stage 4, around 26 S, the striated sarcomere becomes elongated. Stage 5, 1–2 days postfertilization (dpf), myofibrils are bundled through lateral fusion of adjacent myofibrils. Stage 6, around 2 dpf, mature sarcomeres appear after a lateral registration process, as reflected by the formation of well-aligned Z-discs.