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Neuronal function and dysfunction of Drosophila dTDP.

Lin MJ, Cheng CW, Shen CK - PLoS ONE (2011)

Bottom Line: In contrast, overexpression of dTDP in the motor neurons also resulted in reduced larval and adult locomotor activities, but this was accompanied by a decrease of the number of boutons and axon branches at NMJ.On the other hand, constitutive mushroom body-specific knockdown of dTDP expression did not affect the structure of the mushroom bodies, but it impaired the learning ability of the flies, albeit moderately.The effects of mis-expression of dTDP on Drosophila NMJ suggest that eukaryotic TDP-43 guards against over development of the synapses.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.

ABSTRACT

Background: TDP-43 is an RNA- and DNA-binding protein well conserved in animals including the mammals, Drosophila, and C. elegans. In mammals, the multi-function TDP-43 encoded by the TARDBP gene is a signature protein of the ubiquitin-positive inclusions (UBIs) in the diseased neuronal/glial cells of a range of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-U).

Methodology/principal findings: We have studied the function and dysfunction of the Drosophila ortholog of the mammalian TARDBP gene, dTDP, by genetic, behavioral, molecular, and cytological analyses. It was found that depletion of dTDP expression caused locomotion defect accompanied with an increase of the number of boutons at the neuromuscular junctions (NMJ). These phenotypes could be rescued by overexpression of Drosophila dTDP in the motor neurons. In contrast, overexpression of dTDP in the motor neurons also resulted in reduced larval and adult locomotor activities, but this was accompanied by a decrease of the number of boutons and axon branches at NMJ. Significantly, constitutive overexpression of dTDP in the mushroom bodies caused smaller axonal lobes as well as severe learning deficiency. On the other hand, constitutive mushroom body-specific knockdown of dTDP expression did not affect the structure of the mushroom bodies, but it impaired the learning ability of the flies, albeit moderately. Overexpression of dTDP also led to the formation of cytosolic dTDP (+) aggregates.

Conclusion/significance: These data together demonstrate the neuronal functions of dTDP, and by implication the mammalian TDP-43, in learning and locomotion. The effects of mis-expression of dTDP on Drosophila NMJ suggest that eukaryotic TDP-43 guards against over development of the synapses. The conservation of the regulatory pathways of functions and dysfunctions of Drosophila dTDP and mammalian TDP-43 also shows the feasibility of using the flies as a model system for studying the normal TDP-43 function and TDP-43 proteinopathies in the vertebrates including human.

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Learning tests of Drosophila dTDP knockdown and overexpressing flies.The performance indexes of the control OK107>+ flies and flies with mushroom body-specific knockdown (OK107>38377 and OK107>38379) or overexpression (OK107>dTDP#5-1 and OK107>dTDP#18-1) of dTDP were measured by the olfactory learning tests. Note the dramatic lowering of the indexes of the dTDP-overexpressing lines (***, p<0.0001) and the relatively small but significant lowering of the index of OK107>38377 knockdown line (*, p<0.05). All value represented mean ± SD. N = 8 performance indexes per group.
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pone-0020371-g003: Learning tests of Drosophila dTDP knockdown and overexpressing flies.The performance indexes of the control OK107>+ flies and flies with mushroom body-specific knockdown (OK107>38377 and OK107>38379) or overexpression (OK107>dTDP#5-1 and OK107>dTDP#18-1) of dTDP were measured by the olfactory learning tests. Note the dramatic lowering of the indexes of the dTDP-overexpressing lines (***, p<0.0001) and the relatively small but significant lowering of the index of OK107>38377 knockdown line (*, p<0.05). All value represented mean ± SD. N = 8 performance indexes per group.

Mentions: The learning abilities of the above 4 dTDP mutant lines were assayed by the odor avoidance learning test in comparison to the control flies. As shown in Fig. 3, while the lowering of dTDP expression in the mushroom bodies of OK107>38377 by constitutive RNAi knockdown did not cause obvious defective phenotype of the mushroom bodies (Fig. 2C-b), the performance index of learning of this line showed modest (10%) but statistically significant reductions (p<0.05) when compared to the control flies. On the other hand, the olfactory learning abilities of the two dTDP-overexpressing lines were severely impaired when compared to the control. Furthermore, parallel to the structural defects of the mushroom bodies (Fig. 2C), the impairment of the learning ability was dTDP dose-dependent: flies with higher dTDP overexpression (OK107>dTDP#5-1) showed approximately ∼80% reduction in the performance score when compared to the control flies; on the other hand, the lower level of dTDP overexpression, as in OK107>dTDP#18-1, caused only 30% decrease of the learning ability (Fig. 3). The reductions of the learning capabilities of the two independent UAS-dTDP lines also suggested that the disruption of the learning ability was not due to a dominant effect of gene disruption at the insertion site of the transgene. The data of Figs. 2 and 3 together indicated that dTDP likely played a role in the learning function of the mushroom bodies. Furthermore, overexpression of dTDP in the mushroom bodies led to gain-of-negative function of dTDP causing abnormal axon lobe phenotype as well as impaired learning ability, a situation similar to FTLD-U (see Discussion).


Neuronal function and dysfunction of Drosophila dTDP.

Lin MJ, Cheng CW, Shen CK - PLoS ONE (2011)

Learning tests of Drosophila dTDP knockdown and overexpressing flies.The performance indexes of the control OK107>+ flies and flies with mushroom body-specific knockdown (OK107>38377 and OK107>38379) or overexpression (OK107>dTDP#5-1 and OK107>dTDP#18-1) of dTDP were measured by the olfactory learning tests. Note the dramatic lowering of the indexes of the dTDP-overexpressing lines (***, p<0.0001) and the relatively small but significant lowering of the index of OK107>38377 knockdown line (*, p<0.05). All value represented mean ± SD. N = 8 performance indexes per group.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105987&req=5

pone-0020371-g003: Learning tests of Drosophila dTDP knockdown and overexpressing flies.The performance indexes of the control OK107>+ flies and flies with mushroom body-specific knockdown (OK107>38377 and OK107>38379) or overexpression (OK107>dTDP#5-1 and OK107>dTDP#18-1) of dTDP were measured by the olfactory learning tests. Note the dramatic lowering of the indexes of the dTDP-overexpressing lines (***, p<0.0001) and the relatively small but significant lowering of the index of OK107>38377 knockdown line (*, p<0.05). All value represented mean ± SD. N = 8 performance indexes per group.
Mentions: The learning abilities of the above 4 dTDP mutant lines were assayed by the odor avoidance learning test in comparison to the control flies. As shown in Fig. 3, while the lowering of dTDP expression in the mushroom bodies of OK107>38377 by constitutive RNAi knockdown did not cause obvious defective phenotype of the mushroom bodies (Fig. 2C-b), the performance index of learning of this line showed modest (10%) but statistically significant reductions (p<0.05) when compared to the control flies. On the other hand, the olfactory learning abilities of the two dTDP-overexpressing lines were severely impaired when compared to the control. Furthermore, parallel to the structural defects of the mushroom bodies (Fig. 2C), the impairment of the learning ability was dTDP dose-dependent: flies with higher dTDP overexpression (OK107>dTDP#5-1) showed approximately ∼80% reduction in the performance score when compared to the control flies; on the other hand, the lower level of dTDP overexpression, as in OK107>dTDP#18-1, caused only 30% decrease of the learning ability (Fig. 3). The reductions of the learning capabilities of the two independent UAS-dTDP lines also suggested that the disruption of the learning ability was not due to a dominant effect of gene disruption at the insertion site of the transgene. The data of Figs. 2 and 3 together indicated that dTDP likely played a role in the learning function of the mushroom bodies. Furthermore, overexpression of dTDP in the mushroom bodies led to gain-of-negative function of dTDP causing abnormal axon lobe phenotype as well as impaired learning ability, a situation similar to FTLD-U (see Discussion).

Bottom Line: In contrast, overexpression of dTDP in the motor neurons also resulted in reduced larval and adult locomotor activities, but this was accompanied by a decrease of the number of boutons and axon branches at NMJ.On the other hand, constitutive mushroom body-specific knockdown of dTDP expression did not affect the structure of the mushroom bodies, but it impaired the learning ability of the flies, albeit moderately.The effects of mis-expression of dTDP on Drosophila NMJ suggest that eukaryotic TDP-43 guards against over development of the synapses.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.

ABSTRACT

Background: TDP-43 is an RNA- and DNA-binding protein well conserved in animals including the mammals, Drosophila, and C. elegans. In mammals, the multi-function TDP-43 encoded by the TARDBP gene is a signature protein of the ubiquitin-positive inclusions (UBIs) in the diseased neuronal/glial cells of a range of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-U).

Methodology/principal findings: We have studied the function and dysfunction of the Drosophila ortholog of the mammalian TARDBP gene, dTDP, by genetic, behavioral, molecular, and cytological analyses. It was found that depletion of dTDP expression caused locomotion defect accompanied with an increase of the number of boutons at the neuromuscular junctions (NMJ). These phenotypes could be rescued by overexpression of Drosophila dTDP in the motor neurons. In contrast, overexpression of dTDP in the motor neurons also resulted in reduced larval and adult locomotor activities, but this was accompanied by a decrease of the number of boutons and axon branches at NMJ. Significantly, constitutive overexpression of dTDP in the mushroom bodies caused smaller axonal lobes as well as severe learning deficiency. On the other hand, constitutive mushroom body-specific knockdown of dTDP expression did not affect the structure of the mushroom bodies, but it impaired the learning ability of the flies, albeit moderately. Overexpression of dTDP also led to the formation of cytosolic dTDP (+) aggregates.

Conclusion/significance: These data together demonstrate the neuronal functions of dTDP, and by implication the mammalian TDP-43, in learning and locomotion. The effects of mis-expression of dTDP on Drosophila NMJ suggest that eukaryotic TDP-43 guards against over development of the synapses. The conservation of the regulatory pathways of functions and dysfunctions of Drosophila dTDP and mammalian TDP-43 also shows the feasibility of using the flies as a model system for studying the normal TDP-43 function and TDP-43 proteinopathies in the vertebrates including human.

Show MeSH
Related in: MedlinePlus