Novel Computational Methods for the Comparison of Leishmania Genomes and Transcriptomes

Abstract

Leishmania is a genus of protozoan parasites and the causative agent of Leishmaniasis. Twenty-one infectious species have been identified, with many previously being investigated by DNA and RNA-sequencing. However, significant genetic variation has prevented the comparison of this data across Leishmania species. Gene orthology grouping fails to compare over 70% of Leishmania genes’ expression across multiple species because of this variation. Here, we describe a novel method to reliably compare the genomes and transcriptomes of multiple Leishmania. This method produces a hybrid genome from the genetic sequence of any Leishmania species, while containing the rich sequence annotations of the L. major reference genome. In a demonstrative analysis, our approach allowed the comparison of 87% of genes in L. major against 5 other Leishmania species. Significant genetic variation was found to prevent comparison of many virulence-implicated genes, including surface antigens (e.g. amastins), cysteine proteases, and HSP-83. Within genes that could be compared, parasite transcriptomes segregated primarily by developmental stage (promastigote and amastigote). Transcriptomes secondarily separated by species. Genes upregulated in infection across all Leishmania were identified and included surface amastins, methyltransferases, and an apoptosis inhibition factor. Downregulated genes showed significantly greater sequence conservation than upregulated genes and comprised paraflagellar, flagellar, and HSP-70 proteins among others. The transcriptome differences between the clinical manifestations of leishmaniasis were additionally characterized. Taken together, these results provide much needed insight into the shared Leishmania pathway of infection and survival.