Targeted Genome Editing via CRISPR in the Pathogen Cryptococcus neoformans

Area of Science:

• Microbiology
• Molecular Genetics
• Pathogen Research

Background:

• Homologous integration rates in Cryptococcus neoformans have been low for two decades, limiting molecular genetic studies.
• New tools are needed to facilitate genome manipulation in this significant fungal pathogen.

Purpose of the Study:

• To investigate the utility of a Class 2 CRISPR system for genome manipulation in Cryptococcus neoformans.
• To assess the impact of CRISPR-Cas9 expression on C. neoformans growth, virulence factor production, and in vivo virulence.

Main Methods:

• Expression of Streptococcus pyogenes Cas9 nuclease and self-cleaving guide RNAs targeting the ADE2 gene in C. neoformans.
• Testing transient and stable expression of CRISPR constructs.
• Evaluating CRISPR system functionality and its effect on homologous recombination rates.
• Assessing virulence in a murine inhalation model.

Main Results:

• Stable integration of the Cas9 construct is necessary for CRISPR system functionality in C. neoformans.
• Transient expression of guide RNA enhances homologous recombination in a Cas9-expressing background.
• Cas9 nuclease expression does not affect C. neoformans growth, in vitro virulence factor production, or in vivo virulence.

Conclusions:

• The developed CRISPR-Cas9 system is functional in Cryptococcus neoformans.
• This system significantly enhances homologous recombination rates, overcoming previous limitations in genetic studies.
• The CRISPR system is compatible with C. neoformans pathogenesis research and offers a powerful new tool for the field.