TEMPORAL REGULATION OF THE XENOPUS FGF RECEPTOR IN DEVELOPMENT - A TRANSLATION INHIBITORY ELEMENT IN THE 3'-UNTRANSLATED REGION

Early frog embryogenesis depends on a maternal pool of mRNA to execute critical intercellular signalling events, FGF receptor-1, which is re quired for normal development, is stored as a stable, untranslated mat ernal mRNA transcript in the fully grown immature oocyte, but is trans lationally activated at meiotic maturation, We have identified a short cis-acting element in the FGF receptor 3' untranslated region that in hibits translation of synthetic mRNA, This inhibitory element is suffi cient to inhibit translation of heterologous reporter mRNA in the imma ture oocyte without changing RNA stability, Deletion of the poly(A) tr act or polyadenylation signal sequences does not affect translational inhibition by this element, At meiotic maturation, we observe the reve rsal of translational repression mediated by the inhibitory element, m imicking that seen with endogenous maternal FGF receptor mRNA at meios is, In addition, the activation of synthetic transcripts at maturation does not appear to require poly(A) lengthening, We also show that an oocyte cytoplasmic protein specifically binds the 3' inhibitory elemen t, suggesting that translational repression of Xenopus FGF receptor-1 maternal mRNA in the oocyte is mediated by RNA-protein interactions, T hese data describe a mechanism of translational control that appears t o be independent of poly(A) changes.