CAL1 is the Drosophila CENP-A assembly factor

Area of Science:

• Epigenetics
• Molecular Biology
• Chromosomal Biology

Background:

• Centromeres, essential for chromosome segregation, are epigenetically defined by the histone H3 variant CENP-A.
• While conserved HJURP/Scm3 chaperones deposit CENP-A in vertebrates and fungi, these are absent in insects and plants.
• The fly-specific protein CAL1 was previously implicated in centromeric CENP-A deposition in Drosophila.

Purpose of the Study:

• To identify and characterize the function of the missing CENP-A chaperone in Drosophila.
• To elucidate the mechanism by which CAL1 mediates CENP-A deposition and centromere specification.
• To investigate the evolutionary conservation of centromere assembly mechanisms.

Main Methods:

• Targeting CAL1 to non-centromeric DNA in Drosophila cells.
• Assessing recruitment of CENP-A, kinetochore proteins, and microtubule attachments.
• Biochemical analysis of CAL1-CENP-A interactions and nucleosome assembly.
• Mapping CAL1 domains responsible for assembly and centromere targeting.

Main Results:

• Targeting CAL1 to ectopic DNA sites successfully recruited CENP-A, kinetochore proteins, and induced microtubule attachments.
• CAL1 selectively binds CENP-A and facilitates the assembly of functional CENP-A nucleosomes.
• The N-terminal domain of CAL1 mediates CENP-A assembly, while the C-terminus interacts with CENP-C for centromere targeting.

Conclusions:

• CAL1 functions as the essential CENP-A chaperone in Drosophila, analogous to HJURP/Scm3 in other lineages.
• This study identifies a conserved mechanism for centromere specification involving CAL1, bridging insect and vertebrate systems.
• The findings reveal fundamental principles governing epigenetic centromere identity across diverse eukaryotes.