Mutation and selection explain why many eukaryotic centromeric DNA sequences are often A + T rich.

Area of Science:

• Genetics
• Evolutionary Biology
• Molecular Biology

Background:

• Centromeres are crucial for chromosome segregation during cell division.
• The sequence composition and evolutionary dynamics of centromeric DNA are not fully understood.
• Native centromeres in Schizosaccharomyces pombe provide a model for studying centromere function.

Purpose of the Study:

• To investigate the functional requirements of centromeric DNA sequences.
• To explore the evolutionary forces shaping centromere composition across diverse species.
• To determine if A+ T-rich DNA can function as a centromere.

Main Methods:

• Chromosome engineering in fission yeast (Schizosaccharomyces pombe) to replace native centromeric DNA with test sequences.
• Analysis of A+ T content in centromeric DNA across 43 Opisthokonta species.
• Genome size used as a proxy for effective population size (Ne).

Main Results:

• A+ T-rich DNA, both synthetic and bacterial, successfully functions as a centromere in fission yeast.
• The A+ T content of centromeric DNA scales with effective population size (Ne) across Opisthokonta.
• Neo-centromere sequences differ from native centromeric DNA, suggesting distinct establishment or propagation requirements.

Conclusions:

• Most A+ T-rich DNA sequences can function as centromeres in Opisthokonta species.
• A balance between mutation and selection likely determines centromeric A+ T content.
• The plasticity of centromeric DNA sequences may facilitate rapid evolutionary changes.