Hansenula polymorpha cells lacking the ER-localized peroxins Pex23 or Pex29 show defects in mitochondrial function...

Area of Science:

• Cell Biology
• Molecular Biology
• Yeast Genetics

Background:

• Pex23 family proteins are endoplasmic reticulum-localized factors involved in peroxisome and lipid body biogenesis.
• Hansenula polymorpha possesses four Pex23 family members: Pex23, Pex24, Pex29, and Pex32.
• Previous studies indicated Pex24 and Pex32 are essential for peroxisome formation via peroxisome-endoplasmic reticulum contact sites.

Purpose of the Study:

• To investigate the impact of the absence of all four Pex23 family proteins on cellular organelles in Hansenula polymorpha.
• To determine the specific roles of individual Pex23 family members in peroxisome, lipid droplet, and mitochondrial dynamics.
• To elucidate the relationship between Pex23 family proteins and mitochondrion-endoplasmic reticulum interactions.

Main Methods:

• Generation and analysis of single deletion strains for Pex23, Pex24, Pex29, and Pex32 in Hansenula polymorpha.
• Microscopic examination of cellular organelles, including vacuoles, lipid droplets, and mitochondria, in deletion mutants.
• Genetic manipulation, including deletion of DNM1, to assess suppression of observed phenotypes.
• Analysis of mitochondrial activity and cell growth rates.

Main Results:

• Vacuoles remained unaffected in all deletion strains.
• Absence of Pex23 or Pex29, but not Pex24 or Pex32, led to reduced lipid droplet numbers.
• Mitochondria were fragmented and clustered in pex23 and pex29 cells, associated with decreased Fzo1 levels and impaired mitochondrial function.
• Deletion of DNM1 suppressed mitochondrial morphology defects and partially rescued growth retardation in pex23 and pex29 mutants.
• An artificial mitochondrion-endoplasmic reticulum tether partially suppressed growth defects, suggesting altered organelle contact sites.

Conclusions:

• Different Pex23 family members regulate distinct aspects of organelle biogenesis, with Pex23 and Pex29 specifically influencing lipid droplet formation.
• Pex23 and Pex29 are critical for maintaining mitochondrial integrity and function, potentially through regulation of mitochondrion-endoplasmic reticulum contact sites.
• The Pex23 family plays a multifaceted role in cellular organization, extending beyond peroxisomes to impact lipid droplets and mitochondria.