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Fig. 1 Homology of syt4 with homologs in other vertebrate species. (A) Simplified phylogenetic tree of syt4 and syt genes in zebrafish and other vertebrate species including rodents and humans. The complete phylogenetic trees were shown in Supplementary Fig. 1. (B) Alignment of partial peptide sequences of domain C2A, which has 5 calcium binding site labeling 1–5 in the figures. We included several homologs from human (SYT1-3) with no mutation at the third position of calcium biding site to compare with SYT4 and another homolog (SYT11) with substitution. The substitution of calcium biding (aspartic acid (D) to serine (S)) is conserved in zebrafish gene syt4, syt11a and syt11b (third amino acid, red box). We observed an extra substitution at the fifth binding site in zebrafish syt4 (aspartic acid (D) to glutamic acid (E), light blue box) and human SYT11. Conserved amino acids between different species were labeled in different color for an easy visualization.