Mitochondrial inheritance in haploid x non-haploid crosses in Cryptococcus neoformans

Abstract

<p>Cryptococcus neoformans is among the most common human fungal pathogen and the leading cause of meningoencephalitis among immunocompromised individuals. It consists of two divergent serotypes A and D as well as their hybrid serotype AD. Strains of serotype A and D are mostly haploid in the natural environment and among clinical isolates while AD hybrids are either aneuploid or diploid. C. <em>neoformans</em> is a bipolar heterothallic fungus in which completion of the sexual (meiotic) cycle is dependent upon interaction between cells of opposite mating type, MAT<strong>a</strong> and MATα<strong></strong>. In crosses between haploid MAT<strong>a</strong> and MATα strains, most fusion products and meiotic segregants inherit mitochondrial DNA (mtDNA) from the MAT<strong>a</strong> parent. Besides mating between haploid strains, haploid x aneuploid and haploid x diploid crosses, collectively referred to as haploid x non-haploid crosses, can also occur in C. <em>neoformans.</em> However, it was previously unknown whether the uniparental mitochondrial inheritance operates in C. <em>neoformans</em> haploid x non-haploid crosses as well. In my thesis, I analyzed mitochondrial inheritance in the fusant and meiotic segregant populations of the two types of opposite-sex haploid x non-haploid crosses, MAT<strong>a</strong>/<strong>a</strong> and MATα and MAT<strong>a</strong> and MATα/α. The study showed that: (1) unlike haploid x haploid crosses, mitochondrial inheritance in the progeny of haploid x non-haploid crosses was not dominantly uniparental although it was biased towards inheritance of MAT<strong>a</strong>(/<strong>a</strong>) parent-specific mtDNA, and that (2) there was a significant variation within and between crosses of each type in the percent of progeny with other mtDNA types. The findings of my study expand our understanding of mitochondrial inheritance process in C. <em>neoformans</em> and, potentially, in other eukaryotes.</p>