SURAMIN AND HEPARIN - ASPECIFIC INHIBITORS OF MESODERM INDUCTION IN THE XENOPUS-LAEVIS EMBRYO

Xenopus embryos in solutions containing suramin show a dose-dependent decrease in the formation of dorsoanterior structures. Continuous trea tment with 1 mM suramin produces embryos without mesodermal derivative s but with mesenchymal cells. Brief immersions of 20 min were used to determine the most sensitive stages and to establish dose-effect curve s: a 20 min treatment with 3 mM suramin at stages 7-8.5 produces blast ula-like embryos, never classified before, with atypical epidermis, ce lls full of yolk and mesenchyme in between. The lack of dorsal mesoder m was confirmed by an RNase protection assay with ct-cardiac actin pro be. Heparin also causes a reduction in dorsal structures, but its acti on is weaker and and there are also strong toxic effects such as super ficial cell dissociation. The effect of heparin is dose-dependent and brief immersions show a very sensitive period around stage 6.5. The lo west DAI obtained is 1.5, an extremely microcephalic embryo with forke d tail codes, a stocky notochord, and abnormally shaped, abundant neur al tissue. Immunofluorescence shows that the distribution of fibronect in-containing fibrils is normal in heparin-treated embryos, whereas th ere are no such fibrils in suramin-treated embryos at control stage 12 .