Functional DNA array' in the fly: implication for neuronal degeneration

Gain-of-function screen identifies a role of the Sec61alpha translocon in Drosophila postmitotic neurotoxicity

To elucidate the intrinsic mechanisms of neurotoxicity induction, including those underlying neural cell death and neurodegeneration, we developed a gain-of-function screen for gene products causing neural cell loss. To identify novel genes with a cell-death-related function in neurons, we screened 4,964 Drosophila GS lines, in which one or two genes from much of the Drosophila genome can be overexpressed. Approximately 0.68% of the GS lines produced phenotypes involving a loss of postmitotic neurons. Of these, we identified and characterized the endd2 gene, which encodes the Drosophila ortholog of Sec61alpha (DSec61alpha), an endoplasmic reticulum protein with protein translocation activity. Ectopic expression of DSec61alpha caused neural cell death accompanied by the accumulation of ubiquitinated proteins, which was mediated by DSec61alpha's translocon activity. This supported our previous observation that the DSec61alpha translocon contributes to expanded polyglutamine-mediated neuronal toxicity, which is also associated with ubiquitinated protein accumulation. These data suggest that the translocon may be a novel component of neural cell death and degeneration pathways. Our approach can be used to identify potential neurotoxic factors within the whole genome, which will increase our understanding of the molecular mechanisms of various types of cell death, including those associated with human neurodegenerative diseases.

Cytosol-endoplasmic reticulum interplay by Sec61alpha translocon in polyglutamine-mediated neurotoxicity in Drosophila

Intracellular deposition of aggregated and ubiquitinated proteins is a prominent cytopathological feature of most neurodegenerative disorders frequently correlated with neural cell death. To elucidate mechanisms in neural cell death and degeneration, we characterized the Drosophila ortholog of Sec61alpha (DSec61alpha), a component of the translocon that is involved in both protein import and endoplasmic reticulum-associated degradation. Loss-of-function experiments for DSec61alpha revealed that the translocon contributes to expanded polyglutamine-mediated neuronal toxicity, likely resulting from proteasome inhibition and leading to accumulation of ubiquitinated proteins. Taken together, proteasome inhibition by expanded polyglutamine tracts may lead to the accumulation of toxic undegraded proteins normally transported by the Sec61alpha translocon.