Epigenetic inheritance of centromeres.

Area of Science:

• Epigenetics
• Molecular Biology
• Genetics

Background:

• Centromeres are crucial for chromosome segregation but their epigenetic inheritance mechanism remains unclear.
• Centromere identity depends on nucleosomes containing the histone variant CenH3 instead of canonical H3.
• Selfish centromere drive during female meiosis may have driven the evolution of epigenetic centromere inheritance.

Purpose of the Study:

• To investigate the mechanism of epigenetic centromere inheritance.
• To understand the structural and functional properties of CenH3-containing nucleosomes.
• To propose a model for how centromere identity is maintained.

Main Methods:

• Molecular studies of Drosophila and yeast centromeres.
• Analysis of nucleosome structure and DNA supercoiling.
• In vivo functional assays.

Main Results:

• Drosophila CenH3 nucleosomes are half the size of canonical H3 nucleosomes.
• CenH3 nucleosomes induce positive supercoils, unlike H3 nucleosomes which induce negative supercoils.
• Positive supercoiling suggests a right-handed DNA wrap, implying non-octameric structures and exposed surfaces for protein binding.

Conclusions:

• The unique topology of CenH3 nucleosomes likely explains centromere stability and maintenance as unique loci.
• This DNA wrapping mechanism provides a sequence-independent mode of centromere inheritance.
• Incompatibility of opposing nucleosome topologies may prevent centromere drive and ensure faithful inheritance.