Evidence of mRNA-mediated intron loss in the human-pathogenic fungus Cryptococcus neoformans

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• Introns are integral to eukaryotic genomes, but mechanisms of intron gain and loss remain poorly understood.
• The reverse transcription of mRNA followed by homologous recombination is a proposed model for intron loss, yet direct evidence of recent events is scarce.

Purpose of the Study:

• To investigate intron loss mechanisms in Cryptococcus fungi.
• To provide evidence for mRNA-mediated intron loss using comparative genomic analyses.

Main Methods:

• Comparative genome analysis of Cryptococcus gattii and Cryptococcus neoformans (var. grubii and var. neoformans).
• Surveyed gene structures to identify intron conservation and loss events across divergent lineages.

Main Results:

• Identified a recent loss of 10 adjacent introns in a 22-exon gene in Cryptococcus neoformans.
• Found over 99.9% intron conservation across surveyed genomes.
• Observed evidence of intron loss in 20 genes, with no convincing evidence of intron gain.

Conclusions:

• Cryptococcus introns are highly stable over evolutionary timescales.
• Supported the mRNA-mediated intron loss model with evidence from observed loss events.
• Occasional intron loss events occur, primarily through mRNA reverse transcription and integration.