Biology subjects

Ben-Tabou de-Leon, S.

Publications and source records attributed to Ben-Tabou de-Leon, S..

4 recordsLinked to original sources

bioRxiv2020

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

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 vesicle motion and the molecular mechanisms that control it, are not well understood. Sea urchin larval skeletogenesis provides an excellent platform for investigating the kinetics of mineral-bearing vesicles. Here we used lattice light-sheet microscopy to study the three-dimensional (3D) dynamics of calcium-bearing vesicles in the cells of normal sea urchin embryos and of embryos where skeletogenesis is blocked through the inhibition of Vascular Endothelial Growth Factor Receptor (VEGFR). We developed computational tools for displaying 3D-volumetric movies and for automatically quantifying vesicle dynamics. Our findings imply that calcium vesicles perform an active diffusion motion in both, calcifying (skeletogenic) and non-calcifying (ectodermal) cells of the embryo. The diffusion coefficient and vesicle speed are larger in the mesenchymal skeletogenic cells compared to the epithelial ectodermal cells. These differences are possibly due to the distinct mechanical properties of the two tissues, demonstrated by the enhanced f-actin accumulation and myosinII activity in the ectodermal cells compared to the skeletogenic cells. Vesicle motion is not directed toward the biomineralization compartment, but the vesicles slow down when they approach it, and probably bind for mineral deposition. VEGFR inhibition leads to an increase of vesicle volume but hardly changes vesicle kinetics and doesnt affect f-actin accumulation and myosinII activity. Thus, calcium vesicles perform an active diffusion motion in the cell of the sea urchin embryo, with diffusion length and speed that inversely correlate with the strength of the actomyosin network. Overall, our studies provide an unprecedented view of calcium vesicle 3D-dynamics and point toward cytoskeleton remodeling as an important effector of the motion of mineral-bearing vesicles. Authors summaryBiomineralization is a widespread, fundamental process by which organisms use minerals to harden their tissues. Mineral-bearing vesicles were observed in biomineralizing cells and play an essential role in biomineralization, yet little is known about their three-dimensional (3D) dynamics. Here we quantify 3D-vesicle-dynamics during calcite skeleton formation in sea urchin larvae, using lattice-light-sheet microscopy. We discover that calcium vesicles perform a diffusive motion in both calcifying and non-calcifying cells of the embryo. The diffusion coefficient and vesicle speed are higher in the mesenchymal skeletogenic cells compared to the epithelial ectodermal cells. This difference is possibly due to the higher rigidity of the ectodermal cells as demonstrated by the enhanced signal of f-actin and myosinII activity in these cells compared to the skeletogenic cells. The motion of the vesicles in the skeletogenic cells, is not directed toward the biomineralization compartment but the vesicles slow down near it, possibly to deposit their content. Blocking skeletogenesis through the inhibition of Vascular Endothelial Growth Factor Receptor (VEGFR), increases vesicle volume but doesnt change the diffusion mode and the cytoskeleton markers in the cells. Our studies reveal the active diffusive motion of mineral bearing vesicles that is apparently defined by the mechanical properties of the cells. Calcium-vesicle diffusion in biomineralization O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/244053v3_ufig1.gif" ALT="Figure 1"> View larger version (110K): org.highwire.dtl.DTLVardef@15ec7dborg.highwire.dtl.DTLVardef@1931222org.highwire.dtl.DTLVardef@8b8b80org.highwire.dtl.DTLVardef@173bd4d_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2020

The tolerance to hypoxia is defined by a time-sensitive response of the gene regulatory network in sea urchin embryos

Deoxygenation, the reduction of oxygen level in the oceans induced by global warming and anthropogenic disturbances, is a major threat to marine life. This change in oxygen level could be especially harmful to marine embryos that utilize endogenous hypoxia and redox gradients as morphogens during normal development. Here we show that the tolerance to hypoxic conditions changes between different developmental stages of the sea urchin embryo, due to the structure of the gene regulatory networks (GRNs). We demonstrate that during normal development, bone morphogenetic protein (BMP) pathway restricts the activity of the vascular endothelial growth factor (VEGF) pathway to two lateral domains and by that controls proper skeletal patterning. Hypoxia applied during early development strongly perturbs the activity of Nodal and BMP pathways that affect VEGF pathway, dorsal-ventral (DV) and skeletogenic patterning. These pathways are largely unaffected by hypoxia applied after DV axis formation. We propose that the use of redox and hypoxia as morphogens makes the sea urchin embryo highly sensitive to environmental hypoxia during early development, but the GRN structure provides higher tolerance to hypoxia at later stages. Summary statementThe use of hypoxia and redox gradients as morphogens makes sea urchin early development sensitive to environmental hypoxia. This sensitivity decreases later, due to the structure of the gene regulatory network.

developmental biology↗

bioRxiv2019

Developmental transcriptomes of the sea star, Patiria miniata, illuminate the relationship between conservation of gene expression and morphological conservation

Evolutionary changes in developmental gene expression lead to alteration in the embryonic body plan and biodiversity. A promising approach for linking changes in developmental gene expression to altered morphogenesis is the comparison of developmental transcriptomes of closely related and further diverged species within the same phylum. Here we generated quantitative transcriptomes of the sea star, Patiria miniata (P. miniata) of the echinoderm phylum, at eight embryonic stages. We then compared developmental gene expression between P. miniata and the sea urchin, Paracentrotus lividus (~500 million year divergence) and between Paracentrotus lividus and the sea urchin, Strongylocentrotus purpuratus (~40 million year divergence). We discovered that the interspecies correlations of gene expression level between morphologically equivalent stages decreases with increasing evolutionary distance, and becomes more similar to the correlations between morphologically distinct stages. This trend is observed for different sub-sets of genes, from various functional classes and embryonic territories, but is least severe for developmental genes sub-sets. The interspecies correlation matrices of developmental genes show a consistent peak at the onset of gastrulation, supporting the hourglass model of phylotypic stage conservation. We propose that at large evolutionary distance the conservation of relative expression levels for most sets of genes is more related to the required quantities of transcripts in a cell than to conserved morphogenesis processes. In these distances, the information about morphological similarity is reflected mostly in the interspecies correlations between the expressions of developmental control genes.\n\nAuthor summaryUnderstanding the relationship between the interspecies conservation of gene expression and morphological similarity is a major challenge in modern evolutionary and developmental biology. The Interspecies correlations of gene expression levels have been used extensively to illuminate these relationships and reveal the developmental stages that show the highest conservation of gene expression, focusing on the diagonal elements of the correlation matrices. Here we generated the developmental transcriptomes of the sea star, Patiria miniata, and used them to study the interspecies correlations between closely related and further diverged species within the echinoderm phylum. Our study reveals that the diagonal elements of the correlation matrices contain only partial information. The off-diagonal elements, that compare gene expression between distinct developmental stages, indicate whether the conservation of gene expression is indeed related to similar morphology or instead, to general cellular constraints that linger throughout development. With increasing evolutionary distances the diagonal elements decrease and become similar to the off-diagonal elements, reflecting the shift from morphological to general cellular constraints. Within this trend, the interspecies correlations of developmental control genes maintain their diagonality even at large evolutionary distance, and peak at the onset of gastrulation, supporting the hourglass model of phylotypic stage conservation.

evolutionary biology↗

bioRxiv2019

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

Biomineralization is the process in 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 existing components used for other purposes. The mechanistic understanding of the regulatory networks that drive biomineralization and their evolution is far from clear. The 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 under the control the vascular endothelial growth factor (VEGF) signaling. The VEGF pathway controls tubulogenesis and vascularization across metazoans while its regulation of biomineralization was only observed in echinoderms. 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 tubulogenesis during vertebrate vascularization. Human VEGF rescues sea urchin VEGF knock-down; VEGF-dependent vesicle deposition plays a significant role in both systems and sea urchin VEGF signaling activates hundreds of genes including biomineralization and vascularization genes. Five upstream transcription factors and three signaling genes active in spiculogenesis are homologous to vertebrate factors that regulate 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 co-opted for biomineralization in the echinoderm phylum. Significance statementThe sea urchin calcite spicules and vertebrate blood vessels are quite distinct in their function, yet both have a tubular structure and are controlled by the vascular endothelial growth factor (VEGF) pathway. Here we study the downstream program by which VEGF pathway drives sea urchin spiculogenesis and find remarkable similarities to the control of vertebrate vascularization. The similarities are observed both in the upstream gene regulatory network, in the downstream effector genes and the cellular processes that VEGF signaling controls at the site of the calcite spicule formation. We speculate that sea urchin spiculogenesis and vertebrate vascularization diverged from a common ancestral tubulogenesis program that was co-opted for biomineralization in the echinoderm phylum.

evolutionary biology↗