Genetic variability in esag6

Acta Tropica 93 (2005) 63–73

Genetic variability in ESAG6 genes among Trypanosoma evansi isolates and in comparison to other Trypanozoon members
William H. Witolaa , Nopporn Sarataphanb , Noboru Inouec , Kazuhiko Ohashia , Misao Onumaa,∗
a

Laboratory of Infectious Diseases, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan b Parasitology Section,National Institute of Animal Health, Kaset Klang, Bangkhen, Bangkok 10900, Thailand c National Research Centre for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan Received 13 June 2004; received in revised form 12 August 2004; accepted 14 September 2004 Available online 22 October 2004

Abstract Bloodstream trypanosomes take up ironneeded for their propagation through the transferrin receptor that, in Trypanosoma brucei, is encoded by expression-site-associated genes (ESAGs), ESAG6 and 7 genes located in variant surface glycoprotein expression sites. ESAG6 and 7 genes in different expression sites have been shown to encode transferrin receptors with varying affinities for polymorphic transferrins. T. brucei could cope with thedifferent host transferrins by switching between expression sites. ESAG6- and 7-encoded transferrin receptor appear to be present in Trypanosoma evansi but the genes have not yet been characterized. In this study, we cloned and sequenced different members of ESAG6 genes in seven isolates of T. evansi from geographically distinct localities in Thailand. We assessed the intra- and inter-species geneticvariability in the transferrin receptor gene regions involved in transferrin binding and established that T. evansi, like T. brucei, has widely diverse ESAG6 genes. In addition, T. evansi possess a clade of ESAG6 variants not observed in T. brucei and different T. evansi strains share at least two conserved variants. We further noted that T. evansi possesses all the reported T. equiperdum ESAG6variants as a subset. Our findings depict a correlation between the genetic diversity in the transferrin-binding regions of ESAG6 genes with the broad host range of T. evansi and T. brucei compared to the narrow host range of Trypanosoma equiperdum. © 2004 Elsevier B.V. All rights reserved.
Keywords: Trypanosoma evansi; Transferrin receptor; ESAG6 genes; Genetic variability

1. IntroductionCorresponding author. Tel.: +81 11 7065215; fax: +81 11 7065217. E-mail address: monuma@vetmed.hokudai.ac.jp (M. Onuma). 0001-706X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2004.09.006
∗

The flagellated protozoan parasite, Trypanosoma evansi, is widely distributed and infects and cause disease in a variety of mammalian species including

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W.H.Witola et al. / Acta Tropica 93 (2005) 63–73

horses, mules, camels, buffalo, cattle, pigs, dogs, and deer. The disease is endemic in Southeast Asia, Africa and South America where thousands of animals die annually due to the disease (Reid, 2002). T. evansi is much more closely related to Trypanosoma equiperdum than to Trypanosoma brucei based on biochemical and molecular data (Brun et al.,1998). However, T. evansi and T. brucei have a similarly wider host range than T. equiperdum, which only infects equines. Bloodstream trypanosomes utilize the transferrin receptor for the uptake of all the iron they need for propagation (Schell et al., 1991a,b). The transferrin receptor isolated from T. brucei is a heterodimeric glycosylphosphatidylinositol-anchored receptor, that is encoded by twohomologous expression-siteassociated genes (ESAGs), ESAG6 and 7 (Chaudhri et al., 1994; Ligtenberg et al., 1994; Steverding et al., 1994; Salmon et al., 1994). There are as many as 20 pairs of the ESAG6 and 7, equivalent to the number of variant surface glycoprotein (VSG) expression sites, but only one pair is active at a given time (Bitter et al., 1998). The ESAG6 and 7 heterodimers encoded by...