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Rab4 spatially and functionally converges with Rab7 in the degradative endolysosomal network
Stephen M Farmer1,2,3, Shiyu Xu1, Yue Yu1,2
1Center for Metabolic and Degenerative Diseases, The Brown Foundation Institute of Molecular Medicine, McGovern Medical School at the University of Texas Health Science Center at Houston (UTHealth), Houston, Texas, 77030.
Molecular Biology of the Cell
|January 15, 2026
Summary
In Drosophila, Rab4 and Rab7 GTPases colocalize and have opposing effects on endolysosome size. Rab4 also aids degradation by directing cargo into the Rab7 pathway.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Rab GTPases regulate endosomal trafficking in eukaryotes.
- Rab4 is typically associated with early endosomes for recycling, while Rab7 is linked to late endosomes for degradation in mammalian cells.
Purpose of the Study:
- To investigate the localization and function of Rab4 and Rab7 in Drosophila endosomal trafficking.
- To determine the relationship and functional overlap between Rab4 and Rab7 in regulating endolysosome dynamics and cargo processing.
Main Methods:
- Immunofluorescence microscopy to assess colocalization of endogenous Rab4 and Rab7 in Drosophila tissues.
- Genetic manipulation (overexpression and knockout/mutants) of Rab4 and Rab7 to study their effects on endolysosome size and cargo trafficking.
- Analysis of fly viability in different Rab mutant combinations.
- Western blotting to quantify levels of βPS-Integrin in Rab4 mutants and overexpression lines.
- Live imaging of integrin trafficking in mammalian cells and mouse brains.
Main Results:
- Endogenous Rab4 and Rab7 extensively colocalize in Drosophila across tissues and developmental stages.
- Rab4 and Rab7 have opposing effects on endolysosomal size; Rab4 overexpression or Rab7 impairment enlarges them, while Rab4 loss or active Rab7 reduces their size.
- Rab4 deficiency specifically impacts the viability of rab7-deficient flies, indicating functional overlap.
- Rab4 directs cargo like βPS-Integrin into the Rab7-mediated degradation pathway, a role beyond simple recycling.
- Rab4 and Rab7 also colocalize in mammalian cells, with dynamic β1-integrin trafficking observed between these compartments.
Conclusions:
- Contrary to mammalian cells, Rab4 and Rab7 function together in the same endosomal compartments in Drosophila.
- Rab4 plays a dual role in endosomal trafficking, participating in both recycling and degradation pathways via Rab7.
- These findings reveal a conserved functional interplay between Rab4 and Rab7 in regulating endolysosomal cargo processing and organelle size.
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