Bridgin connects the outer kinetochore to centromeric chromatin

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The outer kinetochore links microtubules to centromeric chromatin via specific pathways originating from the constitutive centromere associated network (CCAN).
• Many CCAN components and kinetochore linkers have been lost during the evolution of Basidiomycota fungi.

Purpose of the Study:

• To investigate the mechanisms of kinetochore-chromatin linkage in Basidiomycota, specifically in Cryptococcus neoformans.
• To identify novel kinetochore proteins and elucidate their function in chromosome segregation.

Main Methods:

• Kinetochore interactome analyses in Cryptococcus neoformans.
• In vivo and in vitro functional analyses of identified proteins.

Main Results:

• A novel forkhead-associated domain-containing protein, named "bridgin," was identified as a kinetochore component.
• Bridgin connects the outer kinetochore with centromeric chromatin, ensuring accurate chromosome segregation.
• Bridgin is recruited at the outer kinetochore, representing a distinct family of kinetochore proteins separate from CCAN-based linkers.

Conclusions:

• Bridgin is a novel kinetochore protein essential for chromosome segregation in Basidiomycota.
• The discovery of bridgin highlights a divergent evolutionary strategy for outer kinetochore-centromeric chromatin bridging.
• Homologs of bridgin in non-fungal lineages suggest an ancient origin for this alternative linkage mechanism.