Growth factors reverse developmental arrest by zinc in embryos of the sea urchinHemicentrotus pulcherrimus

Abstract

During sea urchin development, zinc (Zn) ions produce developmentally arrested embryos called permanent blastulae. In this study, the effects of growth factors on Zn-arrested embryos were examined to elucidate the relation between Zn arrest and morphogenesis that is mediated by growth factors. Embryos treated with Zn maintained their spherical form for a few days in the absence of growth factors. When the culture medium was supplemented with horse serum, gastrulation occurred in the Zn-arrested embryos, some of which developed into symmetrical larvae closely resembling normal plutei. The growth factors basic fibroblast growth factor (bFGF), TGF-β1, TGF-β2, and activin A also induced recovery of the Zn-arrested embryos. Of the four growth factors tested, activin showed the most intense activity and allowed development of a radial larva with a thick ciliated band and a partially invaginated archenteron. Histochemical staining with ALPase demonstrated the formation of a morphologically and functionally mature digestive tract in the activin-treated embryos. Immunofluorescent staining showed that spicules formed within the msp130-positive mesenchyme cells in the activin-treated embryos. Reversal of Zn arrest did not occur in embryos cultured with serum albumin. These results suggest that Zn arrests development by inhibiting the initiation of morphogenesis and this is mediated by peptide growth factors.