Gene-based synteny analysis
Synteny information obtained from a gene-based analysis revealed higher conserved synteny between L. sceleratus and T. nigroviridis (Figure 5) than between L. sceleratus and T. rubripes or T. bimaculatus (Figure S14-S15). L. sceleratus’ contigs that are unaligned to T. nigroviridischromosomes in Fig.6, were aligned to unplaced regions of the T. nigrorviridis assembly (Fig. S6).
L. sceleratus lacks SCN4A mutations previously associated with pufferfish TTX resistance
The SCN4A protein has been previously associated with pufferfish TTX resistance, showing that mutations in the core of its ion transport domain led to changes in TTX binding affinity. We performed multiple sequence alignment of the ion transport domain sequences from different Tetraodontiformes species and selected outgroups, including teleosts (SCN4AA and SCN4AB paralogs) and other vertebrates. We found thatL. sceleratus and M. mola lack the previously characterized mutations in domains 1 and 2 in residues outlined in red. In contrast, all Tetraodontiformes show changes in the second to last residue of the domain 4 sequence outlined in red in Fig.7.