The protozoan parasite, Leishmania chagasi, causes the fatal human disease visceral leishmaniasis. L. chagasi express an abundant surface protease GP63, which is important for parasite survival. GP63 is encoded by >18 tandem MSP genes, falling into 3 homologous classes whose expression varies throughout the parasite life cycle. MSPL genes are expressed in logarithmic, whereas MSPS genes are expressed in stationary phase when parasites achieve maximal virulence and express high levels of GP63 protein. Our studies focus on the post-transcriptional mechanisms regulating expression of different MSP gene classes. These include mRNA T½, the efficiency of trans-splicing, and protein T½. Using reporter gene constructs and transfection techniques we are localizing unique sequences in MSP 3'UTRs that interact with regulatory proteins. Additionally, using MALDI-TOF mass spec we are examining products of specific MSP class genes that are expressed in different parasite stages.
An ongoing epidemic of visceral leishmaniasis in northeast Brazil has led to our studies genetic loci associated with different outcomes of human L. chagasi infection (asymptomatic versus fatal). Using molecular genotyping methods (microsatellites, SSCP, RFLP, sequencing) we are examining polymorphic alleles of candidate genes for their contributions to disease susceptibility, in collaboration with Dr. Selma Jeronimo of Natal, Brazil. These studies will extend to a genome-wide scan and fine mapping of loci linked to different disease outcomes.