Structural messenger RNA contains cytokeratin polymerization and depolymerization signals.

We have previously shown that VegT mRNA plays a structural (translation-independent) role in the organization of the cytokeratin cytoskeleton in Xenopus oocytes. The depletion of VegT mRNA causes the fragmentation of the cytokeratin network in the vegetal cortex of Xenopus oocytes. This effect can be rescued by the injection of synthetic VegT RNA into the oocyte. Here, we show that the structural function of VegT mRNA in Xenopus oocyte depends on its combinatory signals for the induction or facilitation and for the maintenance of the depolymerization vs. polymerization status of cytokeratin filaments and that the 300-nucleotide fragment of VegT RNA isolated from the context of the entire molecule induces and maintains the depolymerization of cytokeratin filaments when injected into Xenopus oocytes. A computational analysis of three homologous Xenopus VegT mRNAs has revealed the presence, within this 300-nucleotide region, of a conserved base-pairing (hairpin) configuration that might function in RNA/protein interactions.