Cdc42 controls primary mesenchyme cell morphogenesis in the sea urchin embryo

Proc. Natl. Acad. Sci. U.S.A.

Roopin

et al. 2019

130

Biomineralization is the process by which living organisms use minerals to form hard structures that protect and support them. Biomineralization is believed to have evolved rapidly and independently in different phyla utilizing preexisting components. The mechanistic understanding of the regulatory networks that drive biomineralization and their evolution is 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 generated by the skeletogenic cells controlled by vascular endothelial growth factor (VEGF) signaling. The VEGF pathway is essential for biomineralization in echinoderms, while in many other phyla, across metazoans, it controls tubulogenesis and vascularization. Despite the critical role of VEGF signaling in sea urchin spiculogenesis, the downstream program it activates was largely unknown. Here we study the cellular and molecular machinery activated by the VEGF pathway during sea urchin spiculogenesis and reveal multiple parallels to the regulation of vertebrate vascularization. Human VEGF rescues sea urchin VEGF knockdown, vesicle deposition into an internal cavity plays a significant role in both systems, and sea urchin VEGF signaling activates hundreds of genes, including biomineralization and interestingly, vascularization genes. Moreover, five upstream transcription factors and three signaling genes that drive spiculogenesis are homologous to vertebrate factors that control vascularization. Overall, our findings suggest that sea urchin spiculogenesis and vertebrate vascularization diverged from a common ancestral tubulogenesis program, broadly adapted for vascularization and specifically coopted for biomineralization in the echinoderm phylum.

Section: Discussionmentioning

confidence: 99%

Possible cooption of a VEGF-driven tubulogenesis program for biomineralization in echinoderms

Morgulis

Proc. Natl. Acad. Sci. U.S.A.

Roopin

et al. 2019

130

“…5). Relatedly, the cytoskeleton remodeling proteins, ROCK1 and CDC42, known mediators of VEGF signaling during vascular tubulogenesis (52, 53), are critical to normal spicule formation in the sea urchin embryo (54, 55). Thus, to fully understand the molecular control of calcium vesicle secretion and spicule cavity formation it is critical to study VEGF direct control of cytoskeleton remodeling proteins.…”

Section: Discussionmentioning

confidence: 99%

Possible co-option of a VEGF-driven tubulogenesis program for biomineralization in echinoderms

de-Leon

Sher

et al. 2019

Preprint

12Biomineralization is the process in which living organisms use minerals to form hard 13 structures that protect and support them. Biomineralization is believed to have evolved 14 rapidly and independently in different phyla utilizing existing components used for other 15 purposes. The mechanistic understanding of the regulatory networks that drive 16 biomineralization and their evolution is far from clear. The sea urchin skeletogenesis is an 17 excellent model system for studying both gene regulation and mineral uptake and deposition. 18The sea urchin calcite spicules are formed within a tubular cavity generated by the 19 skeletogenic cells under the control the vascular endothelial growth factor (VEGF) signaling. 20The VEGF pathway controls tubulogenesis and vascularization across metazoans while its 21 regulation of biomineralization was only observed in echinoderms. Despite the critical role of 22 for vascularization and specifically co-opted for biomineralization in the echinoderm phylum. 33 Significance statement 36The sea urchin calcite spicules and vertebrate blood vessels are quite distinct in their function, 37 yet both have a tubular structure and are controlled by the vascular endothelial growth factor 38 (VEGF) pathway. Here we study the downstream program by which VEGF pathway drives 39 sea urchin spiculogenesis and find remarkable similarities to the control of vertebrate 40 vascularization. The similarities are observed both in the upstream gene regulatory network, 41 in the downstream effector genes and the cellular processes that VEGF signaling controls at 42 the site of the calcite spicule formation. We speculate that sea urchin spiculogenesis and 43 vertebrate vascularization diverged from a common ancestral tubulogenesis program that was 44 co-opted for biomineralization in the echinoderm phylum. 45 46 3 47

“…Additionally, Rho1 recruits a RhoGap protein that inactivates Rho1 which leads to the disassembly of the F-actin around the vesicles[60]. Relatedly, inhibition of the sea urchin homolog of ROK completely blocks skeletogenesis, inhibition of the small GTPase CDC42 prevents the formation of the spicule chord and biomineralization, and knockdown of the RhoGap gene, rhogap24l/2 perturbs normal spicule formation[17, 66, 67]. Based on these works and on our observation, we offer the following hypothesis for mineral deposition: The calcium vesicles attach to the inner membrane of the spicule chord, and secret their content by regulated acto-myosin contractions around the vesicle.…”

Section: Discussionmentioning

confidence: 99%

Calcium-vesicles perform active diffusion in the sea urchin embryo during larval biomineralization

Winter

Morgulis

et al. 2020

Preprint

Biomineralization is the process by which organisms use minerals to harden their tissues and provide them with physical support. Biomineralizing cells concentrate the mineral in vesicles that they secret into a dedicated compartment where crystallization occurs. The dynamics of mineral-vesicle motion and the molecular mechanisms that regulate it, are not well understood. Sea urchin larval skeletogenesis provides an excellent platform for the analyses of vesicle kinetics. Here we used calcein labeling and lattice light-sheet microscopy to investigate the three-dimensional (3D) vesicle dynamics in control sea urchin embryos and in Vascular Endothelial Growth Factor Receptor (VEGFR) inhibited embryos, where skeletogenesis is blocked. We developed computational tools for displaying 3D-volumetric movies and for automatically quantifying vesicle dynamics in the different embryonic tissues. Our findings imply that calcium vesicles perform an active diffusion motion in all the cells of the embryo. This mode of diffusion is defined by the mechanical properties of the cells and the dynamic rearrangements of the cytoskeletal network. The diffusion coefficient is larger in the mesenchymal skeletogenic cells compared to the epithelial ectodermal cells, possibly due to the distinct mechanical properties of the two tissues. Vesicle motion is not directed toward the biomineralization compartment, but the vesicles slow down when they approach it, and probably bind for mineral deposition. Under VEGFR inhibition, vesicle volume increases and vesicle speed is reduced but the vesicles continue in their diffusive motion. Overall, our studies provide an unprecedented view of calcium vesicle 3D-dynamics and illuminate possible molecular mechanisms that control vesicle dynamics and deposition.