The Effect Of STE12α Gene On The Virulence Of Cryptococcus Neoformans

Cryptococcus neoformans is a basidiomycetous fungal pathogen which can be found all around the world.Cryptococcus neoformans is an important opportunistic pathogen that causes disease in immunocompromised individuals.In our country,most of the cryptococcosis occur in the immumocompetent host.The incidence of cryptococcosis happened in the patients with acquired immunmdeficiency syndrome(AIDS) has increased significantly during the past decades.The study on the pathogenesis of the cryptoccus neoformans is not sufficient. Currently,the virulence factors of the cryptoccus neoformans which has been studied include growth under37℃,enzyme activity,melanin production and capsule.Cryptococcus neoformans is a fungal human pathogen with a bipolar mating system.Mating gene control the progress of sexual development and reproduction.It also lead the creation of the important pathogen basidiomycetous spore,current study in the Saccharomyces cerevisia show that the procedures of sexual development and reproduction are regulated by mitogen-activated protein kinase(MAPK)cascade. Components of MAP kinase signaling cascades that function in Cryptococcus neoformans have recently been identified.We have identified that the STE12,STE11,STE20 protein act as transcription factor in MAPK cascade.The similar procedure can be found in cryptoccus neoformans.The STE12,STE11, STE20 family protein homolog also exist in the components of MAP kinase signaling cascades.All of the three genes which encode these proteins locate in the range of MAT locus.Components of MAP kinase signaling cascades,STE12 protein,maybe play an important role in the virulence of Cryptococcus neoformans.In the research,we have disrupted the STE12αgene in BLS71(BO) and clinical isolate GJF83(GO) to get the defective strains(GD,BD).Then the STE12αlocus was reconstituted with the wild-type allele by cotransformation to get the reconstituted strains(GR,BR).Female C57BL/6 mouse were injected from tail vein with suspension of each strains.24 hours and 72 hours after injection organs of the mouse (kidney,heart,brain,lung,liver) were taken to homogenated and cultivated on Sabourand medium.Mortalities of the mouse were monitored and colony quantities and colony diameters were measured for comparing the virulence of the six isolates.Indian ink negative staining were made to compare the capsules of different isolates.In this research, STE12αmutant strains exhibit a severe defect in capsular size and colony diameters.But in colony quantities,the defective strains(GD,BD) exhibit more vigorus growth capability.In the most Sabourand mediums colony quantities of defective strains(GD,BD)are more than that of the original strains(GO,BO) and the reconstituted strains(GR,BR).The experiment showed that the mouse injected the defective strains(GD,BD) showed lower survival rate from the comparison of the different survival curves.The result imply that the defective strains(GD,BD) have stronger virulence,...