Molecular Characterization of two argonaute-like proteins in D. discoideum

Dept. Genetics, Kassel University, Heinrich-Plett-Str. 40, 34132 Kassel

Research on RNA mediated gene silencing expanded dramatically since the discovery of RNA Interference. This regulation is driven by different classes of small RNAs e.g. siRNAs, piRNAs or miRNAs and takes place on a transcriptional or posttranscriptional level. Argonaute proteins play an important role in all of these related mechanisms. In D. melanogaster several argonaute proteins are involved in silencing of retrotransposons in the germline.

The social amoeba Dictyostelium discoideum encodes five argonaute proteins(AgnA-E). We investigated the function of AgnA and AgnB in vivo. In agnA KO strains a loss of siRNAs from the LTR retrotransposon DIRS-1 and an enrichment of full length DIRS-1 transcripts is observed. In contrast, we saw an upregulation of siRNAs derived from the retrotransposon Skipper in agnA and in other KOs of the RNAi machinery. One of the microRNA candidates(mica1190) of D. discoideum is enriched in the agnA KO, but a second one(mica1198) is uneffected. AgnA thus appears to have opposing functions in the regulation of siRNAs and a subset of miRNAs. A different class of miRNAs may be controlled by other argonaute proteins.

So far we have not observed any significant effects of an agnB KO on either the developmental phenotype or the expression of small RNAs.