Distinct regulatory states control the elongation of individual skeletal rods in the sea urchin embryo

Background Understanding how gene regulatory networks (GRNs) control developmental progression is a key to the mechanistic understanding of morphogenesis. The sea urchin larval skeletogenesis provides an excellent platform to tackle this question. In the early stages of sea urchin skeletogenesis, skeletogenic genes are uniformly expressed in the skeletogenic lineage. Yet, during skeletal elongation, skeletogenic genes are expressed in distinct spatial sub-domains. The regulation of differential gene expression during late skeletogenesis is not well understood. Results Here we reveal the dynamic expression of the skeletogenic regulatory genes that define a specific regulatory state for each pair of skeletal rods, in the sea urchin Paracentrotus lividus. The vascular endothelial growth factor (VEGF) signaling, essential for skeleton formation, specifically controls the migration of cells that form the postoral and distal anterolateral skeletogenic rods. VEGF signaling also controls the expression of regulatory genes in cells at the tips of the postoral rods, including the transcription factors Pitx1 and MyoD1. Pitx1 activity is required for normal skeletal elongation and for the expression of some of VEGF target genes. Conclusions Our study illuminates the fine-tuning of the regulatory system during the transition from early to late skeletogenesis that gives rise to rod-specific regulatory states.

Automated summary

The study reveals the dynamic expression of skeletogenic regulatory genes that define a specific regulatory state for each pair of skeletal rods in the sea urchin Paracentrotus lividus. Vascular endothelial growth factor (VEGF) signaling is essential for skeleton formation, specifically controlling the migration of cells that form specific skeletal rods. VEGF signaling also regulates the expression of regulatory genes in cells at the tips of certain skeletal rods.