The full-of-bacteria gene is required for phagosome maturation during immune defense in Drosophila

Area of Science:

• Cell Biology
• Immunology
• Genetics

Background:

• Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is a fatal genetic disorder.
• Mutations in VPS33B or VPS16B genes cause ARC syndrome, affecting vacuole fusion.
• These genes encode subunits of the HOPS complex crucial for cellular fusion processes.

Purpose of the Study:

• To investigate the function of the Drosophila full-of-bacteria (fob) gene, a homolog of Vps16B.
• To understand the role of fob in cellular processes, particularly immune defense.
• To explore the link between phagosome maturation defects and ARC syndrome symptoms.

Main Methods:

• Generated null mutations in the Drosophila fob gene.
• Assessed the viability and fertility of fob mutant flies.
• Analyzed the immune response of fob mutant flies, focusing on hemocyte function and bacterial digestion.
• Utilized microscopy and molecular markers (e.g., Rab7) to track phagosome maturation.

Main Results:

• Flies null for fob are viable and fertile but exhibit impaired immunity.
• fob hemocytes engulf bacteria but fail to digest them due to defective phagosome-lysosome fusion.
• Phagosomes in fob cells reach a Rab7-positive stage but do not fully acidify.
• Autophagosome and endosome trafficking to lysosomes remain unaffected in fob cells.

Conclusions:

• The Drosophila fob gene is essential for phagosome maturation, specifically the fusion with late endosomes/lysosomes.
• Defects in phagosome maturation, as seen in fob mutants, may contribute to the recurrent infections observed in ARC syndrome patients.
• This study highlights a conserved role for Vps16B homologues in cellular defense mechanisms.