A Signature-Tagged Mutagenesis (STM)-based murine-infectivity assay for Cryptococcus neoformans

Genome-wide phenotypic profiling of transcription factors and identification of novel targets to control the virulence of Vibrio vulnificus

For successful infection, the life-threatening pathogen Vibrio vulnificus elaborately regulates the expression of survival and virulence genes using various transcription factors (TFs). In this study, a library of the V. vulnificus mutants carrying specific signature tags in 285 TF genes was constructed and subjected to 16 phenotypic analyses. Consequently, 89 TFs affecting more than one phenotype of V. vulnificus were identified. Of these, 59 TFs affected the in vitro survival including growth, stress resistance, biofilm formation and motility, and 64 TFs affected the virulence of V. vulnificus. Particularly, 27 of the 64 TFs enhanced the in vitro hemolytic or cytotoxic activities, and 8 of the 27 TFs also increased the in vivo brine shrimp or murine infectivities of V. vulnificus. Among the eight TFs, HlyU, IscR, NagC, MetJ and Tet2 did not affect the growth of V. vulnificus but still regulated the expression of major exotoxin genes, including rtxA, vvhA and plpA, thereby emerging as potential drug targets for anti-virulence therapies with low selective pressure for developing resistance. Altogether, this study characterized the functions of TFs at a genome-wide scale and identified novel targets to control the virulence of V. vulnificus.

Zinc-binding domain mediates pleiotropic functions of Yvh1 in Cryptococcus neoformans

Yvh1 is a dual-specificity phosphatase (DUSP) that is evolutionarily conserved in eukaryotes, including yeasts and humans. Yvh1 is involved in the vegetative growth, differentiation, and virulence of animal and plant fungal pathogens. All Yvh1 orthologs have a conserved DUSP catalytic domain at the N-terminus and a zinc-binding (ZB) domain with two zinc fingers (ZFs) at the C-terminus. Although the DUSP domain is implicated in the regulation of MAPK signaling in humans, only the ZB domain is essential for most cellular functions of Yvh1 in fungi. This study aimed to analyze the functions of the DUSP and ZB domains of Yvh1 in the human fungal pathogen Cryptococcus neoformans, whose Yvh1 (CnYvh1) contains a DUSP domain at the C-terminus and a ZB domain at the N-terminus. Notably, CnYvh1 has an extended internal domain between the two ZF motifs in the ZB domain. To elucidate the function of each domain, we constructed individual domain deletions and swapping strains by complementing the yvh1Δ mutant with wild-type (WT) or mutated YVH1 alleles and examined their Yvh1-dependent phenotypes, including growth under varying stress conditions, mating, and virulence factor production. Here, we found that the complementation of the yvh1Δ mutant with the mutated YVH1 alleles having two ZFs of the ZB domain, but not the DUSP and extended internal domains, restored the WT phenotypic traits in the yvh1Δ mutant. In conclusion, the ZB domain, but not the N-terminal DUSP domain, plays a pivotal role in the pathobiological functions of cryptococcal Yvh1.