![]() ![]() ( A), schematic diagram showing a cross section of the dorsal part of a vertebrate embryo and the different embryonic territories that contribute to skeletal and vascular tissues. ( G), expression of skeletogenic regulatory genes in adult skeletogenic cells in three echinoderm clades.īone biomineralization and vascular tubulogenesis GRNs in vertebrates. ( F), expression of the skeletogenic regulatory genes in the mesoderm of embryos of different echinoderm clades. ( E), embryonic territories in the sea star (SS). D, embryonic territories in the sea cucumber (SC) and brittle star (BS). C, embryonic territories in the sea urchin (SU) and the pencil sea urchin (PU). Color codes are explained in the figure and in the text. ( C– E), embryonic territories in the different echinoderm clades. ( B), sea urchin larval skeletogenic GRN and differentiation genes with various functions. Enlargement, showing the mineral (gray) concentrated in vesicles and transported to the spicule tubular compartment where it is engulfed within a thin layer of extracellular matrix. The skeletogenic cells (red) form a ring with two lateral skeletogenic clusters where the spicule form. ( A), a scheme showing larval skeleton formation in the sea urchin embryo. Sea urchin skeletogenic GRN and the evolution of echinoderm skeletogenic GRN. These comparisons suggest that biomineralization in deuterostomes evolved through the phylum specific co-option of GRNs that control distinct organic scaffolds to mineralization.īiomineralization evolution gene regulatory networks skeletogenesis tubulogenesis vascularization. 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. 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. Here I compare the GRNs that drive biomineralization and tubulogenesis in echinoderms and in vertebrates. This is strictly different than the organic cartilaginous scaffold that vertebrates mineralize with hydroxyapatite to make their bones. The organic scaffold in which the calcite skeletal elements form in echinoderms is a tubular compartment generated by the syncytial skeletogenic cells. Skeletogenesis in the sea urchin embryo was extensively studied and the underlying GRN shows high conservation within echinoderms, larval and adult skeletogenesis. Comparing the gene regulatory networks (GRNs) that drive biomineralization in different species could illuminate the molecular evolution of biomineralization. Biomineralization is proposed to have evolved independently in different phyla through the co-option of pre-existing developmental programs. Biomineralization is the process in which organisms use minerals to generate hard structures like teeth, skeletons and shells. ![]()
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