Comparison of the expression profiles of promastigotes and axenic amastigotes in Leishmania donovani using serial analysis of gene expression

In this study, we examined the transcriptome of Leishmania donovani promastigotes and axenic amastigotes to identify differentially regulated mRNAs utilizing the serial analysis of gene expression (SAGE). The axenic culture of amastigotes was initiated from stationary phase promastigotes. Transformation from promastigote to amastigote occurred when cultures in Medium 199 (pH 5.5), supplemented with 20% (v/v) fetal bovine serum, were transferred from 26°C to 37°C. A total of 20,299 and 20,132 tags were generated from promastigote and amastigote libraries, respectively. The containing unique genes identified in these two SAGE libraries were 8,615 and 7,835, respectively. Characteristics of the expressed genes' frequency distribution were remarkably similar in both libraries: the most abundant tags (frequency >=20), whose levels were equal to or >1.3% of the identified tags, constituted >23% of the total sequenced tags. Correspondingly, 75.72% or 71.65% of the genes accounted for those tags present at low abundance (frequency = 1) contributed only 32.13% or 27.89% of the total tags. A total of 968 genes (11.2% of the total genes in promastigotes and 12.4% in amastigotes) were recorded to have statistically different transcript levels between promastigotes and axenic amastigotes. Of the 968 distinct total genes, there are 326 promastigote-enriched transcripts and 642 amastigote-enriched mRNAs.