Drosophila Models of Tauopathies: What Have We Learned?

Aggregates of the microtubule-associated protein Tau are neuropathological hallmark lesions in Alzheimer's disease (AD) and related primary tauopathies. In addition, Tau is genetically implicated in a number of human neurodegenerative disorders including frontotemporal dementia (FTD) and Parkinson's disease (PD). The exact mechanism by which Tau exerts its neurotoxicity is incompletely understood. Here, we give an overview of how studies using the genetic model organism Drosophila over the past decade have contributed to the molecular understanding of Tau neurotoxicity. We compare the different available readouts for Tau neurotoxicity in flies and review the molecular pathways in which Tau has been implicated. Finally, we emphasize that the integration of genome-wide approaches in human or mice with high-throughput genetic validation in Drosophila is a fruitful approach

Developmental expression of 4-repeat-Tau induces neuronal aneuploidy in Drosophila tauopathy models

Tau-mediated neurodegeneration in Alzheimer's disease and tauopathies is generally assumed to start in a normally developed brain. However, several lines of evidence suggest that impaired Tau isoform expression during development could affect mitosis and ploidy in post-mitotic differentiated tissue. Interestingly, the relative expression levels of Tau isoforms containing either 3 (3R-Tau) or 4 repeats (4R-Tau) play an important role both during brain development and neurodegeneration. Here, we used genetic and cellular tools to study the link between 3R and 4R-Tau isoform expression, mitotic progression in neuronal progenitors and post-mitotic neuronal survival. Our results illustrated that the severity of Tau-induced adult phenotypes depends on 4R-Tau isoform expression during development. As recently described, we observed a mitotic delay in 4R-Tau expressing cells of larval eye discs and brains. Live imaging revealed that the spindle undergoes a cycle of collapse and recovery before proceeding to anaphase. Furthermore, we found a high level of aneuploidy in post-mitotic differentiated tissue. Finally, we showed that overexpression of wild type and mutant 4R-Tau isoform in neuroblastoma SH-SY5Y cell lines is sufficient to induce monopolar spindles. Taken together, our results suggested that neurodegeneration could be in part linked to neuronal aneuploidy caused by 4R-Tau expression during brain development

Two-color in vivo imaging of photoreceptor apoptosis and development in Drosophila

We report a new two-color fluorescent imaging system to visualize the mosaic adult photoreceptor neurons (PRs) in real-time. Using this method, we examined a collection of 434 mutants and identified genes required for PR survival, planar cell polarity (PCP), patterning and differentiation. We could track the progression of PR degeneration in living flies. By introducing the expression of p35, a caspase inhibitor, we found mutations that specifically activate caspase-dependent death. Moreover, we showed that grh is required in R3 for correct PCP establishment. The "Tomato/GFP-FLP/FRT" method allows high-throughput, rapid and precise identification of survival and developmental pathways in living adult PRs at single-cell resolu

Pin1 modulates oxidative stress-induced dephosphorylation of tau in neurons: Implication of the peptidyl prolyl cis/trans isomerase in a pathological mechanism related to Alzheimer’s disease

info:eu-repo/semantics/publishe

Pin1 deregulation in Alzheimer's disease: A role in the aberrant cell cycle re-entry?

info:eu-repo/semantics/publishe

The peptidylprolyl cis/trans-isomerase Pin1 modulates stress-induced dephosphorylation of Tau in neurons. Implication in a pathological mechanism related to Alzheimer disease.

Deregulation of Tau phosphorylation is a key question in Alzheimer disease pathogenesis. Recently, Pin1, a peptidylprolyl cis/trans-isomerase, was proposed to be a new modulator in Tau phosphorylation in Alzheimer disease. In vitro, Pin1 was reported to present a high affinity for both Thr(P)-231, a crucial site for microtubule binding, and Thr(P)-212. In fact, Pin1 may facilitate Thr(P)-231 dephosphorylation by protein phosphatase 2A through trans isomerization of the Thr(P)-Pro peptide bound. However, whether Pin1 binding to Tau leads to isomerization of a single site or of multiple Ser/Thr(P)-Pro sites in vivo is still unknown. In the present study, Pin1 involvement was investigated in stress-induced Tau dephosphorylation with protein phosphatase 2A activation. Both oxidative (H2O2) and heat stresses induced hypophosphorylation of a large set of phospho-Tau epitopes in primary cortical cultures. In both cases, juglone, a Pin1 pharmacological inhibitor, partially prevented dephosphorylation of Tau at Thr-231 among a set of phosphoepitopes tested. Moreover, Pin1 is physiologically found in neurons and partially co-localized with Tau. Furthermore, in Pin1-deficient neuronal primary cultures, H2O2 stress-induced Tau dephosphorylation at Thr(P)-231 was significantly lower than in wild type neurons. Finally, Pin1 transfection in Pin1-deficient neuronal cell cultures allowed for rescuing the effect of H2O2 stress-induced Tau dephosphorylation, whereas a Pin1 catalytic mutant did not. This is the first demonstration of an in situ Pin1 involvement in a differential Tau dephosphorylation on the full-length multiphosphorylated substrate.info:eu-repo/semantics/publishe

Drosophila Fatty Acid Transport Protein Regulates Rhodopsin-1 Metabolism and Is Required for Photoreceptor Neuron Survival

Tight regulation of the visual response is essential for photoreceptor function and survival. Visual response dysregulation often leads to photoreceptor cell degeneration, but the causes of such cell death are not well understood. In this study, we investigated a fatty acid transport protein (fatp) null mutation that caused adult-onset and progressive photoreceptor cell death. Consistent with fatp having a role in the retina, we showed that fatp is expressed in adult photoreceptors and accessory cells and that its re-expression in photoreceptors rescued photoreceptor viability in fatp mutants. The visual response in young fatp-mutant flies was abnormal with elevated electroretinogram amplitudes associated with high levels of Rhodopsin-1 (Rh1). Reducing Rh1 levels in rh1 mutants or depriving flies of vitamin A rescued photoreceptor cell death in fatp mutant flies. Our results indicate that fatp promotes photoreceptor survival by regulating Rh1 abundance

Elevated Rh1 levels are responsible for PR loss in the <i>fatp</i> mutant.

<p>(A) Western blot analysis of Rh1 in boiled head extracts from control, <i>fatp^{k10307/k10307}</i>, <i>rh1^G69D/+</i> and <i>fatp^{k10307/k10307}</i>/<i>rh1^G69D/+</i> 1 to 11-day-old flies. Tubulin was used as a loading control. (B) Quantification of protein levels. Dimer and oligomer forms of Rh1 were due to the boiling of the extracts. Rh1 levels were twofold higher in the <i>fatp</i> mutant than in the control. The level of Rh1 was substantially lower in the <i>rh1^G69D/+</i> single mutant and in the <i>fatp^{k10307/k10307}</i>/<i>rh1^G69D/+</i> double mutant. (C) Western blot analysis of Rh1 and tubulin in <i>fatp</i> mutant mosaic retina extracts from 5-day-old flies reared from the embryonic stage on control (+VitA) and vitamin A-deficient (-VitA) media. Tubulin was used as a loading control. Rh1 was not detectable in flies reared on vitamin A-deficient medium. (D, E) Visualization of <i>fatp</i> mutant mosaic retina of 5-day-old flies reared from the embryonic stage on control (D) and vitamin A-deficient (E) media using the Tomato/GFP-FLP/FRT method (scale bar = 10 µm). (F) Quantification of mutant PR loss (t-test, n≥12). <i>fatp</i> mutant PR viability was dramatically restored in flies reared on vitamin A-deficient medium. (G–J) Analysis of the loss of <i>fatp^k10307</i>, <i>fatp^k10307 arr2^3/+</i> and <i>fatp^k10307 arr2^3/3</i> double mutant PRs using resin-embedded tangential sections in 34-day-old flies (scale bar = 10 µm). (H) Quantification of PR loss. In the double mutants retinas, PRs were significantly rescued (p = 0.0021 and p = 0.0016, t-test, n = 6).</p

<i>Rh1^G69D</i> rescues PR viability in the <i>fatp</i> mutant.

<p>(A–E) Analysis of the survival of control, <i>fatp^k10307</i>, <i>rh1^G69D/+</i> and <i>fatp^k10307rh1^G69D/+</i> double mutant PRs using the Tomato/GFP-FLP/FRT method in 15-day-old flies (scale bar = 10 µm). (E) Quantification of mutant PR losses (t-test, n≥12). PR loss in the <i>fatp^k10307 rh1^G69D/+</i> double mutant was dramatically lower than in the <i>fatp</i> single mutant. (F–J) Analysis of the survival of control, <i>fatp^k10307</i>, <i>rh1^G69D/+</i> and <i>fatp^k10307 rh1^G69D/+</i> double mutant PRs using resin-embedded tangential sections in 28-day-old flies (scale bar = 10 µm). (J) Quantification of PR loss. Significantly more PRs died in the <i>fatp</i> mutant than in control retina (t-test, n = 6). In the double mutant, PR losses were reduced to control levels. (K–N) Electron microscopy analysis of whole-eye control (K), <i>fatp^k10307</i> (L), <i>rh1^G69D/+</i> (M) and <i>fatp^k10307 rh1^G69D/+</i> (N) mutants in 28-day-old flies (scale bar = 1 µm). Whereas PRs degenerated in <i>fatp^k10307</i> ommatidia (arrow) and were phagocytosed by IOCs (*), PRs survived in <i>fatp^k10307 rh1^G69D/+</i> double mutant flies. Rhabdomeres of <i>rh1^G69D/+</i> and <i>fatp^k10307 rh1^G69D/+</i> outer PRs were reduced in size. Arrowheads show artifactual shadows on the sample.</p