Mitotic processes which restore genome balance in Aspergillus nidulans

Area of Science:

• * Genetics
• * Molecular Biology
• * Mycology

Background:

• * Haploid and diploid strains of Aspergillus nidulans with duplicate chromosome segments exhibit mitotic instability.
• * Previous studies suggested spontaneous deletion as the primary mechanism for restoring genome balance.
• * High-frequency deletion was proposed to be provoked by and confined to excess chromosomal segments.

Purpose of the Study:

• * To investigate the mechanisms of genome imbalance correction in diploid strains with extra, translocated chromosome segments.
• * To rigorously test the association between excess segments and deletions.
• * To determine if mitotic crossing over plays a significant role in eliminating excess segments.

Main Methods:

• * Studied a diploid strain of Aspergillus nidulans homozygous for an extra, translocated chromosome segment.
• * Analyzed variants arising from this strain to identify mechanisms of genome correction.
• * Compared deletion breakpoints with those observed in haploid strains with duplications.

Main Results:

• * Elimination of translocated segments in diploids occurs more frequently via mitotic crossing over than deletion.
• * The studied diploid strain was highly unstable, producing variants with balanced or near-balanced genomes.
• * Variants arose through simultaneous deletions and deletions with novel breakpoints, distinct from haploid strains.

Conclusions:

• * Diverse mechanisms contribute to the correction of genome imbalance during mitosis.
• * Mitotic instability and its resolution are influenced by chromosome segment balance and ploidy.
• * The findings challenge the exclusive role of deletion and highlight mitotic crossing over in managing aneuploidy.