AN ECM-BOUND, PDGF-LIKE GROWTH-FACTOR AND A TGF-ALPHA-LIKE GROWTH-FACTOR ARE REQUIRED FOR GASTRULATION AND SPICULOGENESIS IN THE LYTECHINUSEMBRYO

Growth factors and the extracellular matrix have been shown to fulfill vital developmental roles in many embryonic systems. Our hypothesis i s that a developmental role played by the extracellular matrix in sea urchins may be the binding of a PDGF-like growth factor to promote sig naling activity. We report here that anti-human PDGF-B antibodies and anti-human TGF-alpha antibodies immunoprecipitated specific proteins i solated from Lytechinus embryos. Addition of these antibodies to Lytec hinus embryos inhibited gastrulation and spiculogenesis. The embryos a re sensitive to the antibodies from the four-cell through the hatching blastula stages, which suggests that the TGF-alpha-like and PDGF-Like ligands are required for the early differentiation of the gut and spi cules. We present evidence that the PDGF-like growth factor depends on the extracellular matrix for signaling activity. Synthetic peptides r epresenting the heparan sulfate proteoglycan binding sequence on human PDGE-B were added to Lytechinus embryo cultures to compete for bindin g sites with the endogenous PDGF-like growth factor. The experimental peptide inhibited gastrulation and caused radially arranged multiple s picules to form. Development was unaffected by a control peptide. Thes e studies support our hypothesis and suggest that TGE-alpha-like and P DGE-like growth factors induce signaling events required for sea urchi n gastrulation and spiculogenesis and suggest that an extracellular ma trix-associated PDGE-like growth factor is involved in differentiation along the oral-aboral axis. (C) 1995 Academic Press, Inc.