Endo16 is required for gastrulation in the sea urchin Lytechinus variegatus

The Endo16 gene encodes a large extracellular protein with several functional domains that provide some insight into the role of this protein during embryonic development. We isolated the full-length cDNA sequence from Lytechinus variegatus and utilized morpholinos to further investigate the role of Endo16 during embryonic development in this species. Endo16-deficient embryos failed to undergo gastrulation and the blastocoele became filled with dissociated cells after 24 h of incubation. Moreover, there was a delay in endoderm differentiation as assayed by staining with an antibody that recognizes Endo1. The differentiation of other cell types including oral ectoderm, primary mesenchymal cells (PMC) and secondary mesenchymal cells (SMC) appeared to be normal, although the patterns of protein expression did not resemble control embryos due to the gross morphological abnormalities elicited by the LvEndo16 morpholino. Microinjection of full-length EGFP mRNA with the LvEndo16 morpholino-targeted sequence confirmed that this phenotype can be attributed specifically to the loss of Endo16 protein. Taken together, our data suggest that Endo16 may be required for the cell-extracellular matrix (ECM) interactions that are required for endoderm differentiation in the sea urchin embryo.