Co-chaperone Hsp70/Hsp90 organizing protein (Hop) is Required for Transposon Silencing and piRNA Biogenesis [Gene Regulation]

piRNAs are 26-30nt germ-line specific small non-coding RNAs that have evolutionarily conserved function in mobile genetic element (transposons) silencing and maintenance of genome integrity. Drosophila Hsp70/90 Organizing Protein Homolog (Hop), a co-chaperone, interacts with piRNA binding protein Piwi and mediates silencing of phenotypic variations. However, it is not known if Hop has a direct role in piRNA biogenesis and transposon silencing. Here, we show that knockdown of Hop in the germ-line nurse cells (GLKD) of Drosophila ovaries leads to activation of transposons. Hop GLKD females can lay eggs at the same rate as wild type counterparts but the eggs do not hatch into larvae. Hop GLKD leads to the accumulation of γ-H2Av foci in the germline indicating increased DNA damage in the ovary. We also show that Hop GLKD induced transposon up-regulation is due to inefficient piRNA biogenesis. Based on these results, we conclude that Hop is a critical component of piRNA pathway and it maintains genome integrity by silencing transposons.

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