ROCK controls biomineral growth and regulates VEGF target genes during sea urchin larval skeletogenesis

Biomineralization is the process by which living organisms from the five kingdoms of life use minerals to form hard structures that protect and support them. Despite intensive studies in various model organisms, the molecular mechanisms that control biomineralization are far from clear. Sea urchin skeletogenesis is an excellent model system for studying both gene regulation and mineral uptake and deposition. The sea urchin calcite spicules are formed within a tubular cavity downstream of the Vascular Endothelial Growth Factor (VEGF) signaling. We recently revealed remarkable similarities between the molecular control of sea urchin skeletogenesis and the control of vertebrates’ vascularization. Interestingly, the cytoskeleton remodeling machinery seem to play a central role in both systems, yet, how cytoskeleton remodeling controls sea urchin biomineralization is largely, unknown. Here we show that RhoA Kinase (ROCK), a key regulator of vertebrates’ vascularization, controls biomineral growth and regulates the expression of key VEGF target genes in the sea urchin embryo. The continuous inhibition of ROCK activity leads to skeletal loss, calcium accumulation in the skeletogenic cells and significant downregulation of VEGF target genes. The addition of ROCK inhibitor after spicule initiation results with the branching of ectopic spicules that grow perpendicular to the spicule rods. Thus, during sea urchin skeletogenesis, ROCK activity is critical for biomineral formation, biomineral growth in the proper crystallographic direction and the activation of VEGF target genes. We propose that the cytoskeleton remodeling machinery is a key regulator of biomineralization that strongly affects the structure and the properties of the growing biominerals.