Die Rolle der Proteinen der Tudor-Familie in der Biogenese der piRNAs und in der Erhaltung des Genoms
Zusammenfassung der Projektergebnisse
We have fully achieved the project goal, i.e. to understand the role of Qin in piRNA biogenesis. However, due to unexpected results, the work packages had to be redesigned. We have discovered a non-predicted function for Qin/Kumo as a RNAse and propose the following biological role for it. Disruption of Qin has remarkable consequences on the ping-pong cycle. Either knockout of Qin or deletion of its five extended Tudor domains results in an increase of the sense piRNA fraction for all families of sequenced transposable elements, while the antisense piRNA bias is lost because of a non-functional heterotypic ping-pong cycle. Instead, a homotypic ping-pong occurs between Aub:Aub, where the sense and antisense piRNA both bind to Aub. The same phenotype is observed upon Ago3 deletion. In addition, the transposon families showing an increase in the transcript level upon Qin mutation are all known to require Ago3 for silencing, reinforcing the hypothesis of a functional correlation between Qin and Ago3. Based on our results and on the similarity of the phenotypes for the Qin and Ago3 functional mutants, we propose that Qin is the main endonuclease responsible for the maturation of the sense piRNAs bound to Ago3. In our new model of the ping-pong cycle, the absence of Qin causes the heterotypic ping-pong to halt after the loading of the sense piRNAs on Ago3. Failure to process the 3’ end to yield mature sense piRNAs results in Ago3 stalling and leads to the same phenotype as Ago3 depletion. The excess of sense piRNAs, resulting from the lack of 3’ end processing on Ago3, may rebind to Aub, yielding a futile ping-pong cycle. In support of this model, in Qin mutant ovaries, the excess sense piRNA fraction, with a A bias at position 10, was found to be loaded on Aub.
Projektbezogene Publikationen (Auswahl)
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EXTENDED TUDOR-DOMAINS of the piRNA BIOGENESIS PATHWAY HAVE RNA-SPECIFIC NUCLEASE ACTIVITY. Cold Spring Harbor Laboratory.
Dhimole, Neha; zur Lage, Susanne; Klug, Wilfried & Carlomagno, Teresa
