The Origin and Early Evolution of SCPP Genes and Tissue Mineralization in Vertebrates

Kazuhiko Kawasaki

doi:10.1007/978-981-13-1002-7_17

Abstract

Various secretory calcium-binding phosphoprotein (SCPP) genes are involved in the formation of the bone, dentin, enamel, and enameloid in bony vertebrates. By contrast, no SCPP gene is found in cartilaginous vertebrates. In order to explain this difference, I investigated the origin and early evolution of SCPP genes. First, I examined the phylogeny of SPARC-family genes that include evolutionary precursors of SCPP genes. Then, I analyzed the genomic arrangement of the SCPP genes and three SPARC-family genes, SPARCL1, SPARCL1L1, and SPARCR1. The results are consistent with our previous hypothesis that an SCPP gene-like structure arose in the 5′ half of SPARCL1L1 in a common ancestor of jawed vertebrates, at about the same time as the origin of mineralized skeleton. It is possible that cartilaginous vertebrates secondarily lost early SCPP genes, while bony vertebrates gained various new SCPP genes. Some of these new SCPP genes appear to have specifically involved in scale formation; however, these scale genes were lost in tetrapods.

Highlights

Among cardinal traits evolved in vertebrates is mineralized skeleton, which arose in a common ancestor of jawed vertebrates after the divergence of the lineage leading to modern jawless vertebrates (Fig. 17.1) (Donoghue and Sansom 2002)
The bone was secondarily lost in cartilaginous vertebrates (Eames et al 2007), and enamel is thought to have originated in bony vertebrates (Schultze 2016)
We proposed that secretory calcium-binding phosphoprotein (SCPP) genes arose from the 5′ half of SPARCL1L1 (Kawasaki et al 2017)

Summary

17.1 Introduction

Among cardinal traits evolved in vertebrates is mineralized skeleton, which arose in a common ancestor of jawed vertebrates after the divergence of the lineage leading to modern jawless vertebrates (Fig. 17.1) (Donoghue and Sansom 2002). The bone, dentin, enamel, and enameloid are principal mineralized skeletal tissues (Donoghue and Sansom 2002). Among these tissues, the bone was secondarily lost in cartilaginous vertebrates (Eames et al 2007), and enamel is thought to have originated in bony vertebrates (Schultze 2016).

Kawasaki mineralized skeleton jawed vertebrates jawless

17.2 Materials and Methods

17.3.2 Arrangements of SCPP Genes and SPARC Family Genes in Vertebrate Genomes