Mitochondrial-specific perturbation of Drosophila RNase Z in neurons leads to motor impairments, disrupted learning and neurodegeneration

Clinical studies have linked a rare form of neurological disorder to the highly conserved RNase Z gene, which encodes an endoribonuclease responsible for the processing of nuclear and mitochondrial primary tRNA transcripts. Patients harboring mutant variants of this gene exhibit a spectrum of neurological dysfunction; however, no studies to date have established the causality of RNase Z-linked neuropathology. We employed CRISPR/Cas9 technology to create flies with a neuron-specific knockout of the RNase Z gene, which is rescued with transgenes encoding a wild-type or a mutant copy of RNase Z. Neuronal activity of RNase Z is vital, as mutants display striking morphological abnormalities in central and peripheral neurons, along with attenuated motor circuit function and associative learning performance. Neuron-specific mutations of RNase Z also led to mitochondrial fragmentation and elevated ROS production. By employing the rescue transgene encoding RNase Z devoid of a mitochondrial targeting signal (MTS), we segregated the mitochondrial activity of RNase Z from that in other compartments, allowing us to assess organelle-specific contributions to disease etiology and progression. We found that mutating mitochondrial RNase Z was sufficient to induce the neuropathology in flies, as they recapitulate the salient phenotypes observed in the pan-neuronal mutants. Collectively, our study validates the pathogenicity of mutant RNase Z and establishes mitochondrial-specific contributions to neuropathology.