An optimized temporally controlled Gal4 system in Drosophila reveals degeneration caused by adult-onset neuronal Vps13D knockdown

Mutations in the human gene VPS13D cause the adult-onset neurodegenerative disease ataxia. Our previous work showed that disruptions in the Vps13D gene in Drosophila neurons causes mitochondrial defects. However, developmental lethality caused by Vps13D loss limited our understanding of the long-term physiological effects of Vps13D perturbation in neurons. Here, we optimized a previously generated system to temporally knock down Vps13D expression precisely in adult Drosophila neurons using a modification to the Gal4/UAS system. Adult-onset activation of Gal4 was enacted using the chemically-inducible tool which fuses a destabilization-domain to the Gal4 repressor Gal80 (Gal80-DD). Optimization of the Gal80-DD tool shows that feeding animals the DD-stabilizing drug trimethoprim (TMP) during development and rearing at a reduced temperature maximally represses Gal4 activity. Temperature shift and removal of TMP from the food after eclosion robustly activates Gal4 expression in adult neurons. Using the optimized Gal80-DD system, we find that adult-onset Vps13D RNAi expression in neurons causes the accumulation of mitophagy intermediates, progressive deficits in locomotor activity, early lethality, and brain vacuolization characteristic of neurodegeneration. The development of this optimized system allows us to more precisely examine the degenerative phenotypes caused by Vps13D disruption, and can likely be utilized in the future for other genes associated with neurological diseases whose manipulation causes developmental lethality in Drosophila.

VPS13D-related disorders presenting as a pure and complicated form of hereditary spastic paraplegia

Background

Alterations of vacuolar protein sorting‐associated protein 13 (VPS13) family members including VPS13A, VPS13B, and VPS13C lead to chorea acanthocytosis, Cohen syndrome, and parkinsonism, respectively. Recently, VPS13D mutations were identified as a cause of VPS13D‐related movement disorders, which show several phenotypes including chorea, dystonia, spastic ataxia, and spastic paraplegia.

Methods

We applied whole‐exome analysis for a patient with a complicated form of hereditary spastic paraplegia (HSP) and her unaffected parents. Then, we screened the candidate genes in 664 Japanese families with HSP in Japan.

Results

We first found a compound heterozygote VPS13D mutation and a heterozygote ABHD4 variation in a sporadic patient with spastic paraplegia. Then, we found three patients with VPS13D mutations in two Japanese HSP families. The three patients with homozygous mutations (p.Thr1118Met/p.Thr1118Met and p.Thr2945Ala/p.Thr2945Ala) in the VPS13D showed an adult onset pure form of HSP. Meanwhile, the patient with a compound heterozygous mutation (p.Ser405Arg/p.Arg3141Ter) in the VPS13D showed a childhood onset complicated form of HSP associated with cerebellar ataxia, cervical dystonia, cataracts, and chorioretinal dystrophy.

Conclusion

In the present study, we found four patients in three Japanese families with novel VPS13D mutations, which may broaden the clinical and genetic findings for VPS13D‐related disorders.