Research

Biomineralization had apparently evolved independently in different phyla, using distinct minerals, organic scaffolds and gene regulatory networks (GRNs, Ben-Tabou de-Leon, Cells 2022 ). However, diverse eukaryotes from unicellular organisms, through echinoderms to vertebrates, use the actomyosin network during biomineralization.  We study the role of cytoskeleton remodeling, adhesion and mechanosensing during skeletal elongation in the sea urchin embryo. We believe that distinct GRNs across metazoans had independently employed a common mechanosensing circuit, in response to the increase of the extracellular matrix  stiffness during the evolution of biomineralization.

The 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. We studied the downstream program by which VEGF signaling drives sea urchin spiculogenesis and find remarkable similarities to the control of vertebrate vascularization (Morgulis et al, PNAS 2019). 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 uniquely co-opted for biomineralization in the echinoderm phylum. We now aim to unravel the structure and function of the control system that drives tubulogenesis and biomineralization in the sea urchin embryo. We believe that this will advance the understanding of the molecular control of tubulogenesis and biomineralization, two morphogenesis processes essential for living organisms from animals to plants. Additionally, it will illuminate how ancestral genetic developmental programs are co-opted to generate novel functions that are phylum-specific.

Across the animal kingdom, embryos of closely related species show high morphological similarity despite genetic and environmental distances. Deciphering the molecular mechanisms that underlie morphological conservation and those that support embryonic adaptation are keys to understand developmental robustness and evolution. Comparative studies of developmental gene regulatory networks and gene expression can track the genetic changes that lead to evolutionary novelties. We discovered a striking conservation of the expression kinetics of developmental regulatory genes between two closely related sea urchin species (Gildor and SBD, Plos Genetics, 2015). This tight conservation probably underlies the morphological similarities between the embryos of these species. We uncovered the developmental transcriptome of the Mediterranean sea urchin, P. lividus, (Gildor et al. Marine Genomics 2016) and compare genome-wide gene expression kinetics between two sea urchin species (Malik et al, Dev. Biol. 2017). We extended our studies and compared gene expression dynamics between the two sea urchin species and a sea star species that diverged from the sea urchins 500 million years ago (Gildor et al, IJDB 2017, Gildor et al, Sci. Reports). Interestingly the expression of both developmental and housekeeping genes show significant conservation at this large evolutionary distance, possibly since the general morphology within the echinoderm is largely conserved.