Early response gene expression during differentiation of cultured Leishmania donovani

The promastigote form of the unicellular parasite, Leishmania donovani, mus t differentiate into the amastigote form to establish an infection in a mam malian host. Identification of genes whose expression changes during differ entiation could help reveal mechanisms of Leishmania gene regulation and id entify targets for controlling the diseases caused by this human pathogen. Two genomic clones were isolated, P9 that is more highly expressed in proma stigotes than in axenic amastigotes and A14 that is preferentially expresse d in axenic amastigotes. Analysis of the DNA sequences revealed open readin g frames that would encode 55.5 kDa and 100 kDa proteins, respectively, wit h no homology to known proteins. The mRNA level for these genes during 24 h time courses of parasite differentiation in culture was compared to two ge nes known to be differentially expressed, c-lpk2 and mkk. Changes in RNA le vel occurred within 2 h for each gene and continued in advance of morpholog ical changes. The expression levels of these four genes in axenic amastigot es correlated with results from animal-derived parasites.