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

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 car 1 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 car 1 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.

Endocytosis of Wingless via a dynamin-independent pathway is necessary for signaling in Drosophila wing discs

“…The merged early endosomes containing Wg and DFz2 (10-15 min) in the wing disc are also positive for Rab5 GFP (Fig. S1 F-H), an early endosomal marker (28,29). Hence, these endosomes probably act as sites of colocalization and concentration of Wg and DFz2, even in regions where their surface concentrations are low.…”

Rab11 mediates post-Golgi trafficking of rhodopsin to the photosensitive apical membrane ofDrosophilaphotoreceptors

“…We further observed that RLVs label with GFP-tagged Rab7 (Entchev et al, 2000) (Fig. 2B), an endosomal protein that marks the limiting membrane of MVBs in Drosophila (Sriram et al, 2003) and other systems (Raiborg et al, 2003). RLVs also immunostain for Hrs (Fig.…”

hVps41 and VAMP7 function in direct TGN to late endosome transport of lysosomal membrane proteins

“…The Vps33b-VIPAR-Rab11a complex associates with recycling endosomes and functions in the apical delivery of membrane proteins in polarized cells of humans, mice and zebrafish 42 (and unpublished data of the Klumperman and Gissen labs). Moreover, in yeast and Drosophila, mutations in the core class-C proteins give distinct phenotypes, suggesting that individual subunits have distinct activities 29,39 . Thus, specific HOPS components might function in multiple complexes, located at distinct membranes and mediating separate pathways.…”