SCPP Gene Repertoires in Teleosts and Evolutionary Changes in Bone, Teeth, and Scales

Secretory calcium-binding phosphoprotein (SCPP) genes are involved in bone, tooth, and scale formation in bony vertebrates, including teleosts. Various studies have investigated teleost SCPP genes to pinpoint genetic changes associated with phenotypic changes in mineralized skeletal elements. However, no comprehensive studies have been described to date. Here, SCPP genes were searched in 63 teleost genome sequences. The chromosomal distribution of individual SCPP genes suggests that all SCPP genes, except one, originally formed four clusters after the teleost genome duplication. Subsequently, various SCPP genes were apparently lost in different lineages, and scpp1 and spp1 were the only SCPP genes identified in all investigated teleosts. These 63 teleosts include 10 species with reduced scales, 11 scaleless species, and 2 toothless species. Among them, either scpp7 or gsp37 was missing or non-functional in 9 species with reduced scales, and both scpp7 and gsp37 in all 11 scaleless species. In seahorse and pipefish, which have bone but lost teeth and scales, scpp1, spp1, and only two other SCPP genes were found, while in closely related scaleless but toothed cornetfish, scpp5, scpp3, and odam were additionally identified. These findings suggest vital roles of scpp1 and spp1 in bone, scpp7 and gsp37 in scale, and scpp5, scpp3, and odam in tooth formation. However, many other SCPP genes are also involved in the formation of mineralized tissues and are likely important for some specific features of teeth or scales. It appears that the repertoire of SCPP genes in teleost species underlies diverse conditions of mineralized skeletal elements.