Abstract
The secretory calcium-binding phosphoprotein (SCPP) gene family, which includes genes expressed abundantly in human saliva, evolved alongside major evolutionary milestones in vertebrates. We explored the evolution of saliva-related SCPP genes using genomic and transcriptomic resources, finding previously undocumented convergent gene duplications in primate genomes. These saliva-related genes show signatures of positive selection while neighboring genes remain conserved, suggesting dietary and pathogenic pressures drove adaptive diversification of saliva composition in primates, including humans.
Genes within the secretory calcium-binding phosphoprotein (SCPP) family evolved in conjunction with major evolutionary milestones: the formation of a calcified skeleton in vertebrates, the emergence of tooth enamel in fish, and the introduction of lactation in mammals. The SCPP gene family also contains genes expressed primarily and abundantly in human saliva. Here, we explored the evolution of the saliva-related SCPP genes by harnessing currently available genomic and transcriptomic resources.
Our findings provide insights into the expansion and diversification of SCPP genes, notably identifying previously undocumented convergent gene duplications. In primate genomes, we found additional duplication and diversification events that affected genes coding for proteins secreted in saliva. These saliva-related SCPP genes exhibit signatures of positive selection in the primate lineage while the other genes in the same locus remain conserved. We found that regulatory shifts and gene turnover events facilitated the accelerated gain of salivary expression.
Collectively, our results position the SCPP gene family as a hotbed of evolutionary innovation, suggesting the potential role of dietary and pathogenic pressures in the adaptive diversification of the saliva composition in primates, including humans.