title: Cryptococcus neoformans population includes hybrid strains homozygous at mating-type locus.
abstract: Recent attempts to characterise the hybrid strains of Cryptococcus neoformans have led to the identification of a cryptic population of hybrid strains ('H strains') with double DNA content but only a single mating-type allele. To verify a set of hypotheses concerning their origin, we investigated 14 previously isolated H strains and ten F1-progeny strains arising from H99 and JEC20 mating. The double DNA content was tested by flow cytometry; the presence of only one mating type was tested by amplifying 12 mating-type-specific genes and one gene unlinked with the mating-type locus (URA5). Analysis of the F1 progeny identified two H strains, and electrophoretic karyotyping confirmed the occurrence of genetic recombination. The simultaneous presence of the homozygous and heterozygous loci, and the fact that all of the F1-progeny strains presented a recombinant karyotype, suggest that the H strains originated from the post-meiotic random fusion of two of the four recombinant nuclei. Further studies are required to elucidate the role of the homozygous mating-type loci in the virulence of C. neoformans.
authors.affiliation: Istituto di Igiene e Medicina Preventiva, Università degli Studi di Milano - IRCCS Ospedale Maggiore di Milano, Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Cogliati
authors.forename: Maria Carmela
authors.initials: MC
authors.lastname: Esposto
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Tortorano
authors.forename: Maria Anna
authors.initials: MA
authors.lastname: Viviani
mesh_terms: D003433:Crosses, Genetic; D003455:Cryptococcus neoformans / Q000145:classification* / Q000235:genetics*; D005434:Flow Cytometry; D049770:Genes, Mating Type, Fungal / Q000235:genetics*; D005838:Genotype; D006720:Homozygote; D006801:Humans; D016133:Polymerase Chain Reaction; D011995:Recombination, Genetic