Domain composition of nebulin. In all 53 analyzed species, nebulin contains a unique N-terminal sequence and 8 simple N-terminal repeats, followed by 21–31 super-repeats (each containing 7 simple repeats), 12 constitutive simple repeats, 5–18 Z-repeats, 3 simple repeats, a serine-rich domain, and an SH3 domain. The fifth simple repeat of the penultimate super-repeat is alternatively spliced (Donner et al., 2004; Lindqvist et al., 2020), and both versions of this repeat are present in most species. S12 is known to be alternatively spliced in humans and mice (Donner et al., 2004; Witt et al., 2006; Kiss et al., 2020), and S16–S21 are alternatively spliced in humans (Donner et al., 2004). Most species encode a C-terminal simple repeat shortly after the end of the last super-repeat that had not been annotated in mouse or human nebulin; it contains an actin-binding motif and is present in the majority of species, except for pig, cheetah, trout, and all rodents (ermine, rat, and three mouse species).