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Aberrant lysosomal carbohydrate storage accompanies endocytic defects and neurodegeneration in Drosophila benchwarmer.

Dermaut B, Norga KK, Kania A, Verstreken P, Pan H, Zhou Y, Callaerts P, Bellen HJ - J. Cell Biol. (2005)

Bottom Line: Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions.Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner.We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Lysosomal storage is the most common cause of neurodegenerative brain disease in preadulthood. However, the underlying cellular mechanisms that lead to neuronal dysfunction are unknown. Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions. At the bnch larval neuromuscular junction, we observe similar inclusions and find defects in synaptic vesicle recycling at the level of endocytosis. In addition, loss of bnch slows endosome-to-lysosome trafficking in larval garland cells. In adult bnch flies, we observe age-dependent synaptic dysfunction and neuronal degeneration. Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner. We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

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Loss of bnch leads to severe progressive neurodegeneration. (A–D) Brain and retinal morphology of bnch adult escapers. Eosin and hematoxylin stained horizontal sections of adult heads (A and B). Compared with wild type (A), a severe decrease in the cortical neuronal density is observed in transheterozygous bnch mutant escapers (B). Arrows indicate cortical vacuoles. In mutants (B), the external surface of the medulla is not entirely parallel to the face of the lamina, indicating that the medulla has not rotated properly during development. PAS staining in horizontal sections of the adult retina (C, C′, D, and D′). In the control, normal ommatidial organization is seen with lenses, cone cells, pigment cells, and photoreceptors, but no PAS-positive reaction (C and C′). In a bnch transheterozygous escaper (D), the ommatidia as seen in C are disrupted and is accompanied by a marked accumulation of PAS-positive granules (arrows in D′ compared with C′). Names of optic lobe regions are abbreviated as Re (retina), La (lamina), Me (medulla), Lo (lobula), and Lp (lobula plate). (E–I) Retinal light microscopical sections of bnch mutant eye clones stained with toluidine blue. Homozygous bnch mutant eye tissue of 1-d-old flies (F) displays vacuolar degeneration (arrows), swelling of the cytoplasm and cytoplasmic inclusions. Compared with the lesions of 1-d-old flies (F), there is significant increase in size and number of vacuoles after 30 d (G). Such lesions are never found in 30-d-old control flies (E). 7-d-old bnch mutant eyes consistently demonstrate a significant number of vacuoles (>1/2 size of a single ommatidium) (H). In the presence of Spin-GFP (expressed under control of ey-Gal4) these vacuoles are largely absent (I). An occasional small vacuole is present (<1/2 size of a single ommatidium). The occasional ommatidial loss seen in both bnch mutant eyes and controls is an artifact of the GMR-hid insertion present on the FRT chromosome used to induce clones.
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fig8: Loss of bnch leads to severe progressive neurodegeneration. (A–D) Brain and retinal morphology of bnch adult escapers. Eosin and hematoxylin stained horizontal sections of adult heads (A and B). Compared with wild type (A), a severe decrease in the cortical neuronal density is observed in transheterozygous bnch mutant escapers (B). Arrows indicate cortical vacuoles. In mutants (B), the external surface of the medulla is not entirely parallel to the face of the lamina, indicating that the medulla has not rotated properly during development. PAS staining in horizontal sections of the adult retina (C, C′, D, and D′). In the control, normal ommatidial organization is seen with lenses, cone cells, pigment cells, and photoreceptors, but no PAS-positive reaction (C and C′). In a bnch transheterozygous escaper (D), the ommatidia as seen in C are disrupted and is accompanied by a marked accumulation of PAS-positive granules (arrows in D′ compared with C′). Names of optic lobe regions are abbreviated as Re (retina), La (lamina), Me (medulla), Lo (lobula), and Lp (lobula plate). (E–I) Retinal light microscopical sections of bnch mutant eye clones stained with toluidine blue. Homozygous bnch mutant eye tissue of 1-d-old flies (F) displays vacuolar degeneration (arrows), swelling of the cytoplasm and cytoplasmic inclusions. Compared with the lesions of 1-d-old flies (F), there is significant increase in size and number of vacuoles after 30 d (G). Such lesions are never found in 30-d-old control flies (E). 7-d-old bnch mutant eyes consistently demonstrate a significant number of vacuoles (>1/2 size of a single ommatidium) (H). In the presence of Spin-GFP (expressed under control of ey-Gal4) these vacuoles are largely absent (I). An occasional small vacuole is present (<1/2 size of a single ommatidium). The occasional ommatidial loss seen in both bnch mutant eyes and controls is an artifact of the GMR-hid insertion present on the FRT chromosome used to induce clones.

Mentions: In agreement, we observe severe neuronal loss in histological sections of brains of bnch pharate adults and escapers. This neuronal loss is characterized by a significant decrease in the number of neuronal cell bodies and severe vacuolization in cortical brain layers (Fig. 8, A and B). In addition, the layered architecture of the visual lobe is disrupted (Fig. 8, A and B). The medulla of bnch mutants does not undergo its normal rotation with respect to the antero-posterior axis.


Aberrant lysosomal carbohydrate storage accompanies endocytic defects and neurodegeneration in Drosophila benchwarmer.

Dermaut B, Norga KK, Kania A, Verstreken P, Pan H, Zhou Y, Callaerts P, Bellen HJ - J. Cell Biol. (2005)

Loss of bnch leads to severe progressive neurodegeneration. (A–D) Brain and retinal morphology of bnch adult escapers. Eosin and hematoxylin stained horizontal sections of adult heads (A and B). Compared with wild type (A), a severe decrease in the cortical neuronal density is observed in transheterozygous bnch mutant escapers (B). Arrows indicate cortical vacuoles. In mutants (B), the external surface of the medulla is not entirely parallel to the face of the lamina, indicating that the medulla has not rotated properly during development. PAS staining in horizontal sections of the adult retina (C, C′, D, and D′). In the control, normal ommatidial organization is seen with lenses, cone cells, pigment cells, and photoreceptors, but no PAS-positive reaction (C and C′). In a bnch transheterozygous escaper (D), the ommatidia as seen in C are disrupted and is accompanied by a marked accumulation of PAS-positive granules (arrows in D′ compared with C′). Names of optic lobe regions are abbreviated as Re (retina), La (lamina), Me (medulla), Lo (lobula), and Lp (lobula plate). (E–I) Retinal light microscopical sections of bnch mutant eye clones stained with toluidine blue. Homozygous bnch mutant eye tissue of 1-d-old flies (F) displays vacuolar degeneration (arrows), swelling of the cytoplasm and cytoplasmic inclusions. Compared with the lesions of 1-d-old flies (F), there is significant increase in size and number of vacuoles after 30 d (G). Such lesions are never found in 30-d-old control flies (E). 7-d-old bnch mutant eyes consistently demonstrate a significant number of vacuoles (>1/2 size of a single ommatidium) (H). In the presence of Spin-GFP (expressed under control of ey-Gal4) these vacuoles are largely absent (I). An occasional small vacuole is present (<1/2 size of a single ommatidium). The occasional ommatidial loss seen in both bnch mutant eyes and controls is an artifact of the GMR-hid insertion present on the FRT chromosome used to induce clones.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171373&req=5

fig8: Loss of bnch leads to severe progressive neurodegeneration. (A–D) Brain and retinal morphology of bnch adult escapers. Eosin and hematoxylin stained horizontal sections of adult heads (A and B). Compared with wild type (A), a severe decrease in the cortical neuronal density is observed in transheterozygous bnch mutant escapers (B). Arrows indicate cortical vacuoles. In mutants (B), the external surface of the medulla is not entirely parallel to the face of the lamina, indicating that the medulla has not rotated properly during development. PAS staining in horizontal sections of the adult retina (C, C′, D, and D′). In the control, normal ommatidial organization is seen with lenses, cone cells, pigment cells, and photoreceptors, but no PAS-positive reaction (C and C′). In a bnch transheterozygous escaper (D), the ommatidia as seen in C are disrupted and is accompanied by a marked accumulation of PAS-positive granules (arrows in D′ compared with C′). Names of optic lobe regions are abbreviated as Re (retina), La (lamina), Me (medulla), Lo (lobula), and Lp (lobula plate). (E–I) Retinal light microscopical sections of bnch mutant eye clones stained with toluidine blue. Homozygous bnch mutant eye tissue of 1-d-old flies (F) displays vacuolar degeneration (arrows), swelling of the cytoplasm and cytoplasmic inclusions. Compared with the lesions of 1-d-old flies (F), there is significant increase in size and number of vacuoles after 30 d (G). Such lesions are never found in 30-d-old control flies (E). 7-d-old bnch mutant eyes consistently demonstrate a significant number of vacuoles (>1/2 size of a single ommatidium) (H). In the presence of Spin-GFP (expressed under control of ey-Gal4) these vacuoles are largely absent (I). An occasional small vacuole is present (<1/2 size of a single ommatidium). The occasional ommatidial loss seen in both bnch mutant eyes and controls is an artifact of the GMR-hid insertion present on the FRT chromosome used to induce clones.
Mentions: In agreement, we observe severe neuronal loss in histological sections of brains of bnch pharate adults and escapers. This neuronal loss is characterized by a significant decrease in the number of neuronal cell bodies and severe vacuolization in cortical brain layers (Fig. 8, A and B). In addition, the layered architecture of the visual lobe is disrupted (Fig. 8, A and B). The medulla of bnch mutants does not undergo its normal rotation with respect to the antero-posterior axis.

Bottom Line: Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions.Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner.We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Lysosomal storage is the most common cause of neurodegenerative brain disease in preadulthood. However, the underlying cellular mechanisms that lead to neuronal dysfunction are unknown. Here, we report that loss of Drosophila benchwarmer (bnch), a predicted lysosomal sugar carrier, leads to carbohydrate storage in yolk spheres during oogenesis and results in widespread accumulation of enlarged lysosomal and late endosomal inclusions. At the bnch larval neuromuscular junction, we observe similar inclusions and find defects in synaptic vesicle recycling at the level of endocytosis. In addition, loss of bnch slows endosome-to-lysosome trafficking in larval garland cells. In adult bnch flies, we observe age-dependent synaptic dysfunction and neuronal degeneration. Finally, we find that loss of bnch strongly enhances tau neurotoxicity in a dose-dependent manner. We hypothesize that, in bnch, defective lysosomal carbohydrate efflux leads to endocytic defects with functional consequences in synaptic strength, neuronal viability, and tau neurotoxicity.

Show MeSH
Related in: MedlinePlus