Expressed sequence tag (EST) analysis of the erythrocytic stages of Babesia bovis

Expressed sequence tags(ESTs) provide anefficientway toidentify large numbersof genesexpressed ina specificstageofthe life cycle of an organism. Here we analysed � 13,000 ESTs derived from the erythrocytic stage of the apicomplexan parasite Babesia bovis. The ESTs were clustered in order to obtain information on the expression level of a gene and to increase sequence lengthandreliability.Atotalof3522clusterswereobtainedandannotatedusingBLASTalgorithms.Theclusterswereestimatedto represent � 2600 genes of which in total � 2.1 Mbp sequence information was obtained. Expression levels of the genes, as determinedbythenumbersofESTscontainedwithinacluster,werecomparedtothoseoftheirclosesthomologsintheerythrocytic stageofPlasmodium falciparumandToxoplasmagondiitachyzoites.Pathwaysthatarerepresented relativelyabundantinB.bovis are, amongst others, the purine salvage pathway (displaying characteristics not identified before in apicomplexans), isoprenoid biosynthesisintheapicoplastandmanygenesencodingmitochondrialproteins.EspeciallyremarkableinthelattergrouparetheFtype ATPases ‐ which are hardly expressed in P. falciparum and T. gondii ‐ and two highly expressed glycerol-3-phosphate dehydrogenases creating a shuttle possibly controlling the cytoplasmic NADH/NAD + -ratio. A comparison of known antigenic proteinsfromAustralianandAmericanstrainsofB.boviswiththeIsraelstrainusedhereidentifiesconsiderablesequencevariation in the rhoptry associated protein-1 (RAP-1), merozoite surface proteins of the variable merozoite surface antigen (VMSA) family andsphericalbodyproteins.AnalysisoftheESTclustersrepresentingthevariable erythocyte surfaceantigenfamilyrevealsmany variant transcripts of which a few are dominant. Two putative pseudogenes also seem to be transcribed at high levels. # 2006 Elsevier B.V. All rights reserved.