Hsp90 and its interacting partners in the piRNAs pathway

Hsp90 is a molecular chaperone stabilizing many key regulatory proteins. Recently it was shown that the functional alteration of Hsp90 causes activation of transposons in Drosophila germ cells due to alterations in the piRNA pathway. This disfunction results in the induction of a series of phenotypic variants. Therefore Hsp90 works as suppressor of variability that can be generated by the movement of transposons. Preliminary experiments show that the "heat shock" treatment activates the movement of transposons in Drosophila thus suggesting that stress may trigger a functional shift of Hsp90. To address this point, we performed experiments whose results strongly suggest that a functional shift of Hsp90 induced by stress could be related to the involvement of Hsp90 in complexes that are different in normal and stress conditions. In other words, Hsp90 functions in piRNA pathway in absence of stress, but under stress conditions, its role changes by its interaction with different factors. A further result obtained in this work is the involvement of GW182 in piRNA pathway. GW182 interact with Hsp90 and localizes in nuage where piRNA biogenesis occurs. In addition, Hsp90 disfunction causes GW182 and Vasa delocalization from nuage. Therefore we can speculate that, in piRNA pathway, the functions of these three proteins are interconnected.