Roles Of ACT And ICL Genes In Starvation Response Of Cryptococcus Neoformans

Cryptococcus neoformans is a major opportunistic human fungal pathogen, mainly infecting patients with severe cell immunity deficiency such as AIDS patients and patients receving long-term treatment of large doses of steroid drugs. Cryptococcal yeast is a clinically leading cause of fungal meningitis. C. neoformans cells can survive for years as a latent form in the macrophage of immunocompromised patients and eventually proliferate and spread to the neverous systems causing fatal menagitis if untreated. Previous studies have shown that VPS41 gene plays an essential role in the starvation response in vitro, macrophage survival and pathogenicity of C. neoformans.To identify other components of the VPS41-mediated starvation signaling pathway, digital gene expression (DGE) sequencing was performed to reveal differentially expressed genes in the wide type strain H99 and deletion mutant VPS41A under nitrogen starvation conditions. Two candidate target genes, ACT and ICL encoding acetyl transferase and isocitrate lyase respectively, were independly deleted via homologous recombination. Nitrogen starvation response experiments showed that deletion of ICL or ACT significantly impaired the survival of respective mutant strains. After nitrogen starvation for 48 h, the respective survival rates for the H99, mutant act A and reconstituted strain actA::ACT were 86.93%、4.52%、59.92%, while that of mutant iclA and reconstituted strain icl△::ICL were 5.76%、76.90%. The above results provide strong genetic evidence that both ICL or ACT genes play a crucial role in the proper starvation response of cryptococcal cells in the enviroment. Further elucidation of the functional role of ICL and ACT in the VPS41 starvation signaling pathway will help decipher the molecular mechanism underlying the long term survival of cryptoccal cells in the environment.