RabX1 Organizes a Late Endosomal Compartment that Forms Tubular Connections to Lysosomes Consistent with a "Kiss and...

Area of Science:

• Cell biology
• Molecular mechanisms of endosomal trafficking
• Protein degradation pathways

Background:

• Endocytosed protein degradation relies on "kiss and run" events between late endosomes and lysosomes.
• The molecular machinery governing this "kiss and run" process remains largely unknown.

Purpose of the Study:

• To identify novel regulators of the late endosome-lysosome "kiss and run" mechanism.
• To elucidate the role of RabX1 in organizing endosomal compartments and facilitating protein degradation.

Main Methods:

• Utilized Drosophila melanogaster as a model system to study protein trafficking.
• Investigated the function of RabX1 in the follicular epithelium, analyzing Fasciclin2 degradation.
• Employed genetic manipulation and microscopy to observe endosomal morphology and protein localization.

Main Results:

• Identified RabX1 (small guanosine triphosphatase) as a key organizer of late endosomal tubules connecting to lysosomes.
• RabX1 deficiency impairs Fasciclin2 degradation, leading to its accumulation in enlarged late endosomes.
• RabX1-induced tubule formation is dependent on the V-ATPase proton pump, which is upregulated during epithelial differentiation.

Conclusions:

• RabX1 promotes the formation of dynamic tubular connections that facilitate lysosomal content influx into late endosomes, forming endolysosomes for protein degradation.
• V-ATPase activity is essential for RabX1 tubulation and enhances the endolysosomal pathway's capacity.
• Increased endolysosomal capacity, regulated by RabX1 and V-ATPase, is vital for developmental processes like epithelial morphogenesis.