Rab7: a key to lysosome biogenesis.

Area of Science:

• Cell Biology
• Molecular Biology
• Cellular Compartmentalization

Background:

• Lysosome biogenesis and the organization of late endocytic structures are not fully understood.
• The small GTPase Rab7's role in lysosome association and perinuclear compartment regulation remains unclear.
• Previous studies implicated Rab7 primarily in early to late endosome transport.

Purpose of the Study:

• To investigate the role of Rab7 in lysosome biogenesis and the maintenance of the perinuclear lysosome compartment.
• To determine Rab7's association with lysosomes and its function in regulating their perinuclear localization.
• To elucidate the molecular mechanisms by which Rab7 influences late endocytic structure organization.

Main Methods:

• Transient expression of Enhanced Green Fluorescent Protein (EGFP)-tagged Rab7 wild-type and mutant proteins in HeLa cells.
• Analysis of lysosome localization, aggregation, and fusion using microscopy and colocalization studies.
• Assessment of lysosome acidity and accessibility to endocytosed molecules.

Main Results:

• EGFP-Rab7 wild-type and active mutants localized to late endocytic structures/lysosomes, promoting their perinuclear aggregation and fusion.
• Dominant-negative Rab7 mutants disrupted the perinuclear lysosome aggregate, leading to dispersed, acidified, and inaccessible lysosomes.
• Early endosomes, late endosomes, and the trans-Golgi network remained unaffected by Rab7 manipulation.

Conclusions:

• Rab7 is demonstrated to be essential for the maintenance of the perinuclear lysosome compartment.
• Rab7 controls the aggregation and fusion of late endocytic structures, directly impacting lysosome organization.
• These findings reveal a critical role for Rab7 in regulating lysosome positioning and function within the cell.