Cryptococcus neoformans, Unlike Candida albicans, Forms Aneuploid Clones Directly from Uninucleated Cells under Fluconazole Stress

The gold standard of cryptococcosis treatment consists of induction therapy with amphotericin B followed by lifelong maintenance therapy with fluconazole (FLC). However, prolonged exposure to FLC induces the emergence of clones heteroresistant to azoles. All the heteroresistant clones thus far analyzed have been shown to be aneuploids, but how the aneuploid is formed remains unclear. Aneuploidy in fungi and other eukaryotic cells is known to result most commonly from chromosome missegregation during cell division due to defects in any one of the multiple components and processes that are required for the formation of two genetically identical daughter cells. Although formation of multinucleated cells has been observed in cells exposed to FLC, evidence for the emergence of drug-resistant aneuploid populations directly from such cells has been lacking. We show the evidence that the aneuploid in fluconazole-heteroresistant clones ofCryptococcus neoformans is derived neither from multinucleated cells nor from chromosome missegregation.