mRNA Destabilization: The Role of the 3?UTR in Post-transcriptional Regulation of Wnt8 Transcripts

wnt8 is essential for normal embryonic development in vertebrates: severe developmental malformations occur when wnt8 is either over- or under- expressed. Therefore, wnt8 has to be activated at a specific time and for a specific duration to promote proper development. While Wnt8 signaling is regulated at several levels, factors that regulate the extent or duration of Wnt8 signaling are not well understood. One possible mechanism is through the action of microRNAs (miRNAs), 21-22 bp oligomers that are complementary to particular mRNA binding sites found in the 3' untranslated regions (3' UTRs) of target transcripts. The binding of miRNAs to specific sites in mRNAs causes one of two fates: the mRNA is degraded or translation of the transcript is suppressed. The zebrafish wnt8 locus is complex and produces transcripts with alternative 3' UTR elements, each of which has several putative miRNA binding sites. To advance our understanding of wnt8 regulation, we are testing whether the zebrafish wnt8 3'UTR elements destabilize wnt8 transcripts, and we will pinpoint the UTR sequences that mediate this function. Our results indicate that the zebtrafish wnt8 3' UTRs destabilize transcripts in a similar fashion and in a sequence dependent manner. This mode of regulation is not tissue restricted. By making deletions, it was found that one of these alternate 3' UTRs contains much of its activity within a 5' portion that is 120 nucleotides in length. However, this portion does not recapitulate all of the UTR activity which is indicative of a synergistic effect of multiple regulatory elements such as through miRNAs