P58-A and P58-B: Novel proteins that mediate skeletogenesis in the sea urchin embryo

► P58-A and P58-B are novel proteins that mediate skeletogenesis in the sea urchin. ► The P58 proteins are expressed only in the primary mesenchyme cells of embryos. ► P58-A and P58-B are not involved in PMC specification or migration. ► P58-A and P58-B are involved directly in biomineralization during skeletogenesis.