In the study of differential gene expression of Cryptococcus neoformans, a transcript of COX1 (cytochrome oxidase c subunit 1) was identified in a serotype A strain. The transcript was upregulated at 37˚C compared to 30˚C and expressed by yeasts infecting the central nervous system. Northern analysis of COX1 from the serotype A strain revealed two polycistronic transcripts, a temperature-upregulated 2?3 kb transcript and a 1?9 kb transcript that was not affected by temperature. In contrast, COX1 in a serotype D strain showed only a 1?9 kb polycistronic transcript plus a 1?6 kb monocistronic message, and temperature had no effect on the transcripts. The sequence of COX1 revealed similar coding regions between the two strains, but the serotype D strain had five introns whereas no introns were found in the serotype A strain. The serotype D strain had reduced growth rates compared to the serotype A strain at 37˚C, but in an AD hybrid strain the serotype D COX1 gene could support efficient high temperature growth. These studies have revealed mitochondrial molecular differences between serotype A and D strains which show evolutionary divergence. It will be important to determine whether differences in mitochondrial structure and function can influence cryptococcosis.
INTRODUCTIONCryptococcus neoformans is an encapsulated yeast with a propensity for invading the central nervous system of healthy and immunocompromised individuals. Since the beginning of the AIDS pandemic (in the early 1980s), the occurrence of cryptococcal infection has increased sharply, and although several antifungal drugs, including amphotericin B, flucytosine, fluconazole and itraconazole, have shown moderate efficacy in treatment of this infection, a significant number of relapses and treatment failures still occur (Perfect, 1989). The discovery of new antifungal agents which selectively kill or inhibit the growth of C. neoformans in the host is needed for more effective management of this serious and sometimes fatal infection.Recent studies into the pathobiology of C. neoformans have established effective molecular tools to examine the pathogenicity of this fungus and thus identify potential genetic targets for drugs (Chang et al., 1996; Chang & KwonChung, 1994;Lodge et al., 1994;Odom et al., 1997; Salas et al., 1996). Several C. neoformans genes disrupted by targeted gene replacement have now been shown to be associated with the pathogenicity of this yeast. Some examples are those for capsule formation (Chang et al., 1996), laccase for melanin production (Salas et al., 1996), urease , phospholipase and mannose metabolism (Wills et al., 2001). Signal transduction pathways for control of virulence include calcineurin (Odom et al., 1997), GPA1 (Alspaugh et al., 1997), PKA1 (D' Souza et al., 2001) and RAS1 (Alspaugh et al., 2000), which regulate genes for the three major virulence phenotypes of capsule, melanin and growth at 37˚C.The specific hypothesis for this study is that detectable changes in gene expression directed by certain pathobiologic...