An alternative strategy for trypanosome survival in the mammalian bloodstream revealed through genome and transcriptome analysis of the ubiquitous bovine parasite trypanosoma (megatrypanum) theileri

Abstract

There are hundredsofTrypanosoma species that live inthebloodandtissue spacesof their vertebrate hosts. The vast majorityof these donot have theornate systemof antigenic variation thathas evolvedinthe smallnumberofAfrican trypanosomespecies,but can still maintain long-term infections in the face of the vertebrate adaptive immune system. Trypanosoma theileri is a typical example, has a restricted host range of cattle and other Bovinae, and is only occasionally reported to cause patent disease although no systematic survey of the effect of infection on agricultural productivity has been performed. Here, a detailed genome sequence and a transcriptome analysis of gene expression in bloodstream form T. theileri have been performed. Analysis of the genome sequence and expression showed that T. theileri has a typical kinetoplastid genome structure and allowed a prediction that it is capable ofmeiotic exchange, gene silencing via RNA interference and, potentially, density-dependent growth control. In particular, the transcriptome analysishas allowed a comparison oftwo distinct trypanosomecell surfaces, T.brucei andT. theileri, thathave each evolved to enable the maintenance of a long-term extracellular infection in cattle. The T. theileri cell surface can be modeled to contain a mixture of proteins encoded by four novel large and divergent gene families and by members of a major surface protease gene family. This surface composition isdistinct fromtheuniformvariant surface glycoprotein coatonAfrican trypanosomes providing aninsight into a second mechanism used by trypanosome species that proliferate in an extracellularmilieu in vertebrate hosts to avoid the adaptive immune response.