The RNA-binding protein TDP-43 has been linked to amyotrophic lateral sclerosis (ALS) both as a causative locus and as a marker of pathology. With several missense mutations being identified within TDP-43, efforts have been directed towards generating animal models of ALS in mouse, zebrafish, Drosophila and worms. Previous loss of function and overexpression studies have shown that alterations in TDP-43 dosage recapitulate hallmark features of ALS pathology, including neuronal loss and locomotor dysfunction. Here we report a direct in vivo comparison between wild-type and A315T mutant TDP-43 overexpression in Drosophila neurons. We found that when expressed at comparable levels, wild-type TDP-43 exerts more severe effects on neuromuscular junction architecture, viability and motor neuron loss compared with the A315T allele. A subset of these differences can be compensated by higher levels of A315T expression, indicating a direct correlation between dosage and neurotoxic phenotypes. Interestingly, larval locomotion is the sole parameter that is more affected by the A315T allele than wild-type TDP-43. RNA interference and genetic interaction experiments indicate that TDP-43 overexpression mimics a loss-of-function phenotype and suggest a dominant-negative effect. Furthermore, we show that neuronal apoptosis does not require the cytoplasmic localization of TDP-43 and that its neurotoxicity is modulated by the proteasome, the HSP70 chaperone and the apoptosis pathway. Taken together, our findings provide novel insights into the phenotypic consequences of the A315T TDP-43 missense mutation and suggest that studies of individual mutations are critical for elucidating the molecular mechanisms of ALS and related neurodegenerative disorders.
"t that this mutation was identified in only one patient with sporadic ALS ( Kabashi et al . , 2008 ) , we think its pathogenic nature should be taken with caution . However , given that we studied neuronal requirement and func - tional complementation of TDP - 43 , we cannot exclude there may be a cell - type specific requirement , as suggested by Estes et al . ( 2011 ) who observed toxicity when expressing this mutant selectively in glia in Drosophila ."
"Expressing either WT or A315T mutant TDP-43 causes mislocalization and aggregate formation in axons of eye imaginal disks, with WT TDP-43-expressing flies exhibiting more severe aggregation. Estes et al. (2011) Upregulation of endogenous chaperones reduces TDP-43 and TDP-25-associted phenotypes, including cellular aggregation. Gregory et al. (2012) Larvae overexpressing dTDP-43 produce a different expression profile in Drosophila CNS than larvae carrying dTDP-43-null mutants. "
[Show abstract][Hide abstract] ABSTRACT: For over a century Drosophila melanogaster, commonly known as the fruit fly, has been instrumental in genetics research and disease modeling. In more recent years, it has been a powerful tool for modeling and studying neurodegenerative diseases, including the devastating and fatal amyotrophic lateral sclerosis (ALS). The success of this model organism in ALS research comes from the availability of tools to manipulate gene/protein expression in a number of desired cell-types, and the subsequent recapitulation of cellular and molecular phenotypic features of the disease. Several Drosophila models have now been developed for studying the roles of ALS-associated genes in disease pathogenesis that allowed us to understand the molecular pathways that lead to motor neuron degeneration in ALS patients. Our primary goal in this review is to highlight the lessons we have learned using Drosophila models pertaining to ALS research.
Brain Research 10/2014; 1607. DOI:10.1016/j.brainres.2014.09.064 · 2.84 Impact Factor
"One possibility explaining the less severe effects we observe upon expression of wild-type TDP-43 is that wild-type TDP-43 autodownregulates the expression of endogenous TDP-43 (tbph), thus compensating for the increased HDAC6 levels (Ayala et al., 2011). Another possibility is that the pathogenic TDP43 proteins localize differently in comparison to the wild-type TDP-43, harboring additional or stronger effects on HDAC6 mRNA (Estes et al., 2011; Kim et al., 2010). The extent to which either of these mechanisms is at play in fly motor neurons needs to be further explored in the future. "
[Show abstract][Hide abstract] ABSTRACT: Presynaptic densities are specialized structures involved in synaptic vesicle tethering and neurotransmission; however, the mechanisms regulating their function remain understudied. In Drosophila, Bruchpilot is a major constituent of the presynaptic density that tethers vesicles. Here, we show that HDAC6 is necessary and sufficient for deacetylation of Bruchpilot. HDAC6 expression is also controlled by TDP-43, an RNA-binding protein deregulated in amyotrophic lateral sclerosis (ALS). Animals expressing TDP-43 harboring pathogenic mutations show increased HDAC6 expression, decreased Bruchpilot acetylation, larger vesicle-tethering sites, and increased neurotransmission, defects similar to those seen upon expression of HDAC6 and opposite to hdac6 null mutants. Consequently, reduced levels of HDAC6 or increased levels of ELP3, a Bruchpilot acetyltransferase, rescue the presynaptic density defects in TDP-43-expressing flies as well as the decreased adult locomotion. Our work identifies HDAC6 as a Bruchpilot deacetylase and indicates that regulating acetylation of a presynaptic release-site protein is critical for maintaining normal neurotransmission.
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