Investigation of Cryptococcus neoformans magnesium transporters reveals important role of vacuolar magnesium transporter in regulating fungal virulence factors.

Cryptococcus neoformans is an important opportunistic fungal pathogen in humans. Recent studies have demonstrated that metals are critical factors for the regulation of fungal virulence in hosts. In this study, we systemically investigated the function of C. neoformans magnesium transporters in controlling the intracellular Mg balance and virulence-associated factors. We identified three Mg transporters in C. neoformans: Mgt1, Mgt2, and Mgt3. While we could not detect a Mg2+ -related growth phenotype in mgt1 and mgt3 knockout strains, a GAL7p-Mgt2 strain showed significant Mg-dependent growth defects in the presence of glucose. Further analysis demonstrated that MGT2 is a homolog of MNR2 in Saccharomyces cerevisiae, which is localized to the vacuolar membrane and participates in intracellular Mg transport. Interestingly, a transcriptome analysis showed that Mgt2 influenced the expression of 19 genes, which were independent of Mg2+ . We showed that melanin synthesis in C. neoformans required Mg2+ and Mgt2, and that capsule production was negatively regulated by Mg2+ and Mgt2. Repressing the expression of MGT2-induced capsule, which resulted in an increased fungal burden in the lungs. Cumulatively, this study sets the stage for further evaluation of the important role of Mg homeostasis in the regulation of melanin and capsule in C. neoformans.

[Gene cloning, sequence analysis and tissue expression of estrogen-related receptor alpha (Erralpha) in Japanese medaka and its transcriptional responses after differential EDCs exposure].

Endocrine disrupting chemicals (EDCs) can bind or block nuclear receptors in the body and subsequently affect growth, development and reproduction of fish. Estrogen-related receptors (ERRs), belonging to the nuclear receptor superfamily, have been implicated in diverse physiological processes in estrogen signal pathway in mammals, while little is known about them in fishes. Complete mRNA sequence of ERRalpha from medaka (Oryzias latipes) was cloned, and the sequence is similar to those of other vertebrates, especially that the DNA-binding domain (DBD) of ERRalpha is highly conserved among the vertebrates (97.4%-100% sequence identities) and the ligand-binding domain (LBD) of medaka ERRalpha is 66.4%-67.0% sequence identities with those of mammals. The DBD of medaka ERRalpha is of the same length and has high sequence identity with those of estrogen receptor (ERalpha and ERbeta) and androgen receptor (ARalpha and ARbeta) of medaka, but much difference was found between the LBD of medaka ERRalpha with those of ERalpha, ERbeta, ARalpha and ARbeta. ERRalpha gene is located in chromosome 14 and is consisted of 5 exons. The expressions of ERRalpha in different tissues and the transcriptional responses of ERRalpha in testis of medaka exposed differential EDCs were studied by quantitative real-time RT-PCR. ERRalpha is expressed at apparently high levels in gonad, brain, eye, spleen and intestine, though it was broadly expressed in tissues. Significant transcriptional difference was found between testis and ovary, implying ERRalpha would be involved in sex differentiation and gonad development in fish. After 3 weeks exposure of medaka to 200 ng/L ethynylestradiol (EE2), 200 ng/L estrone (E1), 200 ng/L diethylstilbestrol (DES), 100 microg/L atrazine (AT) and 200 ng/L 17beta-estradiol (E2), transcripts of ERRalpha were significantly decreased to 0.54, 0.56, 0.61, 0.63 and 0.65 of control (p < 0.05) in the testes, respectively. And those in the 1 microg/L tributyltin (TBT) and 1 microg/L triphenyltin (TPT) exposure groups were up-regulated to 1.34 and 1.35 folds of control (p > 0.05), respectively. These results suggested that ERRalpha would take actions in the disruption of sex differentiation and gonad development in fish by EDCs. In addition, no multiple steroid hormone-response element half-sites was found in medaka, which were reported in the upstream of ERRalpha gene in mammals, indicating there would be different regulation patters of ERRalpha between teleost and mammal.