Schematic of sarcomere structure. Sarcomeres are the functional units of cardiomyocytes. Each sarcomere contains rows of interdigitating thin (pink) and thick (yellow) filaments comprised of actin and myosin, respectively. Each titin protein (cyan) spans half-sarcomeres from the Z-disc to the M-line.

Schematic of the human TTN gene (meta-transcript) and the two zebrafish titin genes, ttna and ttnb. Titin contains four sub-domains (Z-line, I-band, A-band, M-line) that are conserved between humans and zebrafish. The locations of mutations in the zebrafish ttna and ttnb genes are indicated by arrows and labelled according to published mutant allele names (see Table 1 for more details). Phenotype data are available for embryonic mutants in all lines; yellow stars denote mutant lines in which cardiac function has also been evaluated in adult fish. Additional double mutant lines have also been generated by Shih et al. (2016) including xu068, xu069, xu070 and xu071, each of which possesses different combinations of the xu064, xu065, xu066 and xu067 alleles indicated in this figure (see Table 1 for more details).