A novel role for Celf1 in vegetal RNA localization during Xenopus oogenesis

The localization of certain mRNAs to the vegetal cortex of Xenopus oocytes is of crucial importance for germ cell development and early embryonic patterning. Vegetal RNA localization is mediated by cis-acting RNA localization elements (LE). Several proteins assemble on the RNA LE and direct transport to the vegetal cortex. Although a number of localization RNP components have been identified, their full composition is unknown. In an RNA affinity purification approach, using the dead end 1 (dnd1) RNA LE, we identified Xenopus Celf1 as a novel component of vegetal localization RNP complexes. Celf1 is part of an RNP complex together with known vegetal localization factors and shows specific interactions with LEs from several but not all vegetally localizing RNAs. Immunostaining experiments reveal co-localization of Celf1 with vegetally localizing RNA and with known localization factors. Inhibition of Celf1 protein binding by localization element mutagenesis as well as Celf1 overexpression interfere with vegetal RNA localization. These results argue for a role of Celf1 in vegetal RNA localization during Xenopus oogenesis.