XB-ART-52877RNA. January 1, 2017; 23 (4): 504-520.
Xenopus Piwi proteins interact with a broad proportion of the oocyte transcriptome.
Piwi proteins utilize small RNAs (piRNAs) to recognize target transcripts such as transposable elements (TE). However, extensive piRNA sequence diversity also suggests that Piwi/piRNA complexes interact with many transcripts beyond TEs. To determine Piwi target RNAs, we used ribonucleoprotein-immunoprecipitation (RIP) and cross-linking and immunoprecipitation (CLIP) to identify thousands of transcripts associated with the Piwi proteins XIWI and XILI (Piwi-protein-associated transcripts, PATs) from early stage oocytes of X. laevis and X. tropicalis Most PATs associate with both XIWI and XILI and include transcripts of developmentally important proteins in oogenesis and embryogenesis. Only a minor fraction of PATs in both frog species displayed near perfect matches to piRNAs. Since predicting imperfect pairing between all piRNAs and target RNAs remains intractable, we instead determined that PAT read counts correlate well with the lengths and expression levels of transcripts, features that have also been observed for oocyte mRNAs associated with Drosophila Piwi proteins. We used an in vitro assay with exogenous RNA to confirm that XIWI associates with RNAs in a length- and concentration-dependent manner. In this assay, noncoding transcripts with many perfectly matched antisense piRNAs were unstable, whereas coding transcripts with matching piRNAs were stable, consistent with emerging evidence that Piwi proteins both promote the turnover of TEs and other RNAs, and may also regulate mRNA localization and translation. Our study suggests that Piwi proteins play multiple roles in germ cells and establishes a tractable vertebrate system to study the role of Piwi proteins in transcript regulation.
PubMed ID: 28031481
PMC ID: PMC5340914
Article link: RNA.
Grant support: R00 HD057298 NICHD NIH HHS , R01 AG052465 NIA NIH HHS , R01 GM086434 NIGMS NIH HHS , R01 GM108548 NIGMS NIH HHS , P30 NS045713 NINDS NIH HHS
Genes referenced: piwil1 piwil2