On the origins of congenic MATα and MATa strains of the pathogenic yeast Cryptococcus neoformans

The basidiomycetous yeast Cryptococcus neoformans infects humans and causes a meningoencephalitis that is uniformly fatal if untreated. The organism has a defined sexual cycle involving mating of haploid MATa and MAT alpha strains, gene disruption by transformation and homologous recombination is now readily accomplished, and robust animal models for infection have been well established. In addition, a pair of congenic MAT alpha and MATa haploid strains have been constructed that permit detailed studies on physiology and virulence by classical genetic approaches. These strains represent a valuable resource for further studies in this organism, and the genomic sequence of one of these strains, JEC21 (=B-4500), was recently chosen to be sequenced by an international consortium. Because of the importance of these strains for genetic studies in C, neoformans and the fact that the genomic sequence of one of these strains is in progress, we review here how these congenic strains were originally constructed, (C) 1999 academic Press.