ALS and piRNA 1
The piRNAs, small non-coding RNAs, were thought to be restricted to germline cells. Although they have recently been found in somatic cells including neurons, it is still unclear how piRNA biogenesis is involved in neuronal diseases. Here, we examined possible role of Aubergine (Aub), a Piwi-family protein (PIWI) responsible for piRNA biogenesis in pathogenesis of ALS by using Drosophila ALS model targeting of Cabeza (Caz), Drosophila FUS. Overexpression of Aub enhanced the mobility defects accompanied with anatomical defects in motoneuron at neuromuscular junction induced by neuron-specific knockdown of Caz. To elucidate molecular basis of these observations, we examined the levels of pre-piRNAs and mature-piRNAs under these conditions. The qRT-PCR and RNA-seq analyses revealed that neuron-specific Caz-knockdown increased the pre-piRNAs, while it reduced the mature-piRNAs in the central nervous system (CNS), suggesting that Caz plays a role in production of pre-piRNA. Overexpression of Aub did not increase the level of the mature-piRNAs. These results suggest that the accumulated pre-piRNAs are abnormal abortive pre-piRNAs that cannot be further processed by PIWIs including Aub. We also demonstrated the association of Caz with the pre-piRNAs in the CNS by RNA immunoprecipitation. Immunocytochemical analyses also revealed that overexpression of Aub induced abnormal cytoplasmic localization of Caz. Based on these results, we propose a model that Caz-knockdown-induced abnormal pre-piRNAs associates with Caz, then translocate and accumulate in cytoplasm that is likely mediated by Aub. The novel roles of Caz and Aub found here by using fly ALS model may contribute to understand the pathogenesis of ALS.