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deep-orange and carnation define distinct stages in late endosomal biogenesis in Drosophila melanogaster.

Sriram V, Krishnan KS, Mayor S - J. Cell Biol. (2003)

Bottom Line: However, removal of Dor from small sized Car-positive endosomes is slowed, and subsequent fusion with tubular lysosomes is abolished.Overexpression of Dor in car1 mutant aggravates this defect, implicating Car in the removal of Dor from endosomes.This suggests that, in addition to an independent role in fusion with tubular lysosomes, the Sec1p homologue, Car, regulates Dor function.

View Article: PubMed Central - PubMed

Affiliation: National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560 065, India.

ABSTRACT
Endosomal degradation is severely impaired in primary hemocytes from larvae of eye color mutants of Drosophila. Using high resolution imaging and immunofluorescence microscopy in these cells, products of eye color genes, deep-orange (dor) and carnation (car), are localized to large multivesicular Rab7-positive late endosomes containing Golgi-derived enzymes. These structures mature into small sized Dor-negative, Car-positive structures, which subsequently fuse to form tubular lysosomes. Defective endosomal degradation in mutant alleles of dor results from a failure of Golgi-derived vesicles to fuse with morphologically arrested Rab7-positive large sized endosomes, which are, however, normally acidified and mature with wild-type kinetics. This locates the site of Dor function to fusion of Golgi-derived vesicles with the large Rab7-positive endocytic compartments. In contrast, endosomal degradation is not considerably affected in car1 mutant; fusion of Golgi-derived vesicles and maturation of large sized endosomes is normal. However, removal of Dor from small sized Car-positive endosomes is slowed, and subsequent fusion with tubular lysosomes is abolished. Overexpression of Dor in car1 mutant aggravates this defect, implicating Car in the removal of Dor from endosomes. This suggests that, in addition to an independent role in fusion with tubular lysosomes, the Sec1p homologue, Car, regulates Dor function.

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Schematic of the biogenesis of Rab7-positive endolysosomal system in Drosophila hemocytes. The Drosophila scavenger receptor and markers of the fluid phase are internalized by independent endocytic pathways (Guha et al., 2003) and subsequently colocalize in Rab7-positive MVBs in a 5-min pulse of the two probes. These structures are Dor- and Car-positive and are capable of fusion. Multivesicular late endosomes are also accessed by Golgi-derived pro–cathepsin L via a heterotypic fusion reaction. They mature into smaller electron-dense organelles (t1/2 ∼12 min) and subsequently lose Dor reactivity but remain Car positive. This organelle eventually fuses with a tubular-vesicular Rab7-positive structure; at 2 h the degradation-competent tubular vesicular lysosomes are devoid of Car. Dor (and possibly Car) plays a specific role in endosomal delivery of Golgi- derived cargo (heterotypic fusion). Car regulates Dor membrane association; modulation of Dor governs the morphological progression of the multivesicular bodies to small sized organelles. Car is also involved independent of Dor in fusion of small sized endosomes with tubular lysosomal components. Colored boxes to the left of the model indicate molecular labels of the morphologically distinct endosomes.
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fig11: Schematic of the biogenesis of Rab7-positive endolysosomal system in Drosophila hemocytes. The Drosophila scavenger receptor and markers of the fluid phase are internalized by independent endocytic pathways (Guha et al., 2003) and subsequently colocalize in Rab7-positive MVBs in a 5-min pulse of the two probes. These structures are Dor- and Car-positive and are capable of fusion. Multivesicular late endosomes are also accessed by Golgi-derived pro–cathepsin L via a heterotypic fusion reaction. They mature into smaller electron-dense organelles (t1/2 ∼12 min) and subsequently lose Dor reactivity but remain Car positive. This organelle eventually fuses with a tubular-vesicular Rab7-positive structure; at 2 h the degradation-competent tubular vesicular lysosomes are devoid of Car. Dor (and possibly Car) plays a specific role in endosomal delivery of Golgi- derived cargo (heterotypic fusion). Car regulates Dor membrane association; modulation of Dor governs the morphological progression of the multivesicular bodies to small sized organelles. Car is also involved independent of Dor in fusion of small sized endosomes with tubular lysosomal components. Colored boxes to the left of the model indicate molecular labels of the morphologically distinct endosomes.

Mentions: Together with observations made in a separate study (Guha et al., 2003), these observations show that endocytosed probes in larval hemocytes are first delivered to a collection of Rab7-negative early endosomes followed by subsequent delivery to Rab7-positive multivesicular late endosomes. After a chase of 1 h (or 2 h), probes are visualized in Rab7-positive lysosomal network that is a tubular-vesicular system in live cells (Fig. 2). Although, these endosomal stages are persistently labeled by Rab7, they exhibit a characteristic dynamic of multiple molecular players as detailed below (see Fig. 11).


deep-orange and carnation define distinct stages in late endosomal biogenesis in Drosophila melanogaster.

Sriram V, Krishnan KS, Mayor S - J. Cell Biol. (2003)

Schematic of the biogenesis of Rab7-positive endolysosomal system in Drosophila hemocytes. The Drosophila scavenger receptor and markers of the fluid phase are internalized by independent endocytic pathways (Guha et al., 2003) and subsequently colocalize in Rab7-positive MVBs in a 5-min pulse of the two probes. These structures are Dor- and Car-positive and are capable of fusion. Multivesicular late endosomes are also accessed by Golgi-derived pro–cathepsin L via a heterotypic fusion reaction. They mature into smaller electron-dense organelles (t1/2 ∼12 min) and subsequently lose Dor reactivity but remain Car positive. This organelle eventually fuses with a tubular-vesicular Rab7-positive structure; at 2 h the degradation-competent tubular vesicular lysosomes are devoid of Car. Dor (and possibly Car) plays a specific role in endosomal delivery of Golgi- derived cargo (heterotypic fusion). Car regulates Dor membrane association; modulation of Dor governs the morphological progression of the multivesicular bodies to small sized organelles. Car is also involved independent of Dor in fusion of small sized endosomes with tubular lysosomal components. Colored boxes to the left of the model indicate molecular labels of the morphologically distinct endosomes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172926&req=5

fig11: Schematic of the biogenesis of Rab7-positive endolysosomal system in Drosophila hemocytes. The Drosophila scavenger receptor and markers of the fluid phase are internalized by independent endocytic pathways (Guha et al., 2003) and subsequently colocalize in Rab7-positive MVBs in a 5-min pulse of the two probes. These structures are Dor- and Car-positive and are capable of fusion. Multivesicular late endosomes are also accessed by Golgi-derived pro–cathepsin L via a heterotypic fusion reaction. They mature into smaller electron-dense organelles (t1/2 ∼12 min) and subsequently lose Dor reactivity but remain Car positive. This organelle eventually fuses with a tubular-vesicular Rab7-positive structure; at 2 h the degradation-competent tubular vesicular lysosomes are devoid of Car. Dor (and possibly Car) plays a specific role in endosomal delivery of Golgi- derived cargo (heterotypic fusion). Car regulates Dor membrane association; modulation of Dor governs the morphological progression of the multivesicular bodies to small sized organelles. Car is also involved independent of Dor in fusion of small sized endosomes with tubular lysosomal components. Colored boxes to the left of the model indicate molecular labels of the morphologically distinct endosomes.
Mentions: Together with observations made in a separate study (Guha et al., 2003), these observations show that endocytosed probes in larval hemocytes are first delivered to a collection of Rab7-negative early endosomes followed by subsequent delivery to Rab7-positive multivesicular late endosomes. After a chase of 1 h (or 2 h), probes are visualized in Rab7-positive lysosomal network that is a tubular-vesicular system in live cells (Fig. 2). Although, these endosomal stages are persistently labeled by Rab7, they exhibit a characteristic dynamic of multiple molecular players as detailed below (see Fig. 11).

Bottom Line: However, removal of Dor from small sized Car-positive endosomes is slowed, and subsequent fusion with tubular lysosomes is abolished.Overexpression of Dor in car1 mutant aggravates this defect, implicating Car in the removal of Dor from endosomes.This suggests that, in addition to an independent role in fusion with tubular lysosomes, the Sec1p homologue, Car, regulates Dor function.

View Article: PubMed Central - PubMed

Affiliation: National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560 065, India.

ABSTRACT
Endosomal degradation is severely impaired in primary hemocytes from larvae of eye color mutants of Drosophila. Using high resolution imaging and immunofluorescence microscopy in these cells, products of eye color genes, deep-orange (dor) and carnation (car), are localized to large multivesicular Rab7-positive late endosomes containing Golgi-derived enzymes. These structures mature into small sized Dor-negative, Car-positive structures, which subsequently fuse to form tubular lysosomes. Defective endosomal degradation in mutant alleles of dor results from a failure of Golgi-derived vesicles to fuse with morphologically arrested Rab7-positive large sized endosomes, which are, however, normally acidified and mature with wild-type kinetics. This locates the site of Dor function to fusion of Golgi-derived vesicles with the large Rab7-positive endocytic compartments. In contrast, endosomal degradation is not considerably affected in car1 mutant; fusion of Golgi-derived vesicles and maturation of large sized endosomes is normal. However, removal of Dor from small sized Car-positive endosomes is slowed, and subsequent fusion with tubular lysosomes is abolished. Overexpression of Dor in car1 mutant aggravates this defect, implicating Car in the removal of Dor from endosomes. This suggests that, in addition to an independent role in fusion with tubular lysosomes, the Sec1p homologue, Car, regulates Dor function.

Show MeSH
Related in: MedlinePlus