GSE39203
A role for Fkbp6 and the chaperone machinery in piRNA amplification and transposon silencing
Epigenetic silencing of transposons by Piwi-interacting RNAs (piRNAs) constitutes an RNA-based genome defense mechanism. Piwi endonuclease action amplifies the piRNA pool by generating new piRNAs from target transcripts by a poorly understood mechanism. Here, we identified mouse Fkbp6 as a factor in this biogenesis pathway delivering piRNAs to the Piwi protein Miwi2. Mice lacking Fkbp6 derepress LINE1 (L1) retrotransposon and display reduced DNA methylation due to deficient nuclear accumulation of Miwi2. Like other co-chaperones, Fkbp6 associates with the molecular chaperone Hsp90 via its tetratricopeptide repeat (TPR) domain. Inhibition of the ATP-dependent Hsp90 activity in an insect cell culture model results in the accumulation of short antisense RNAs in Piwi complexes. We identify these to be by-products of piRNA amplification that accumulate only in nuage-localized Piwi proteins. We propose that the chaperone machinery normally ejects these inhibitory RNAs, allowing turnover of Piwi complexes for their continued participation in piRNA amplification. Overall design: Small RNAs were purified for preparation of high-throughput sequencing libraries. All libraries except JX56, JX57, JX36 and JX37 were generated from isolated small RNAs obtained by immunoprecipitation of the indicated proteins (Mili, Miwi2, Siwi or Ago3). JX56 and JX57 were prepared from small RNAs extracted from mouse testis. JX36 and JX37 were prepared from polyA+ RNAs extracted from the Bombyx mori cell line BmN4. Libraries prepared from mouse were prepared from mice having the indicated genotype. BmN4 cells were treated with the Hsp90 inhibitor geldanamycin (GA) before performing the immunoprecipitation in the indicated libraries. This lead to accumulation to a short species of small RNAs (16nt long) in Ago3 complexes which we called ping-pong by-product. Details can be found in Xiol et al. 2012, Molecular Cell.