The Evolution of Biomineralization through the Co-Option of Organic Scaffold Forming Networks

Biomineralization is the process in which organisms use minerals to generate hard structures like teeth, skeletons and shells. Biomineralization is proposed to have evolved independently in different phyla through the co-option of pre-existing developmental programs. Comparing the gene regulatory networks (GRNs) that drive biomineralization in different species could illuminate the molecular evolution of biomineralization. Skeletogenesis in the sea urchin embryo was extensively studied and the underlying GRN shows high conservation within echinoderms, larval and adult skeletogenesis. The organic scaffold in which the calcite skeletal elements form in echinoderms is a tubular compartment generated by the syncytial skeletogenic cells. This is strictly different than the organic cartilaginous scaffold that vertebrates mineralize with hydroxyapatite to make their bones. Here I compare the GRNs that drive biomineralization and tubulogenesis in echinoderms and in vertebrates. The GRN that drives skeletogenesis in the sea urchin embryo shows little similarity to the GRN that drives bone formation and high resemblance to the GRN that drives vertebrates' vascular tubulogenesis. On the other hand, vertebrates' bone-GRNs show high similarity to the GRNs that operate in the cells that generate the cartilage-like tissues of basal chordate and invertebrates that do not produce mineralized tissue. These comparisons suggest that biomineralization in deuterostomes evolved through the phylum specific co-option of GRNs that control distinct organic scaffolds to mineralization.

Automated summary

Biomineralization is the process by which organisms create hard structures using minerals. It is believed to have independently evolved in different phyla through the co-option of pre-existing developmental programs. A comparison of the gene regulatory networks (GRNs) involved in biomineralization in different species can shed light on its molecular evolution. In this study, the GRNs driving biomineralization and tubulogenesis in echinoderms and vertebrates were compared. The results show that the GRN driving skeletogenesis in sea urchin embryos is different from the GRN driving bone formation in vertebrates, but resembles the GRN driving vascular tubulogenesis in vertebrates. On the other hand, the bone-GRNs in vertebrates are similar to the GRNs operating in the cells that generate cartilage-like tissues in basal chordates and invertebrates that do not produce mineralized tissue. These comparisons suggest that biomineralization in deuterostomes evolved through the phylum-specific co-option of GRNs that control different organic scaffolds for mineralization.