Molecular mechanisms of diversity of theileria parasite genes distributed in middle and South America

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Theileria sergenti is a tick-borne protozoa of cattle. Benign bovine theileria parasites, which are presumed to be of the T. sergenti / buffeli / orientalis group are distributed in Asian countries. The parasites have the major piroplasm surface protein (MPSP) gene which is one of the means of parasite evasion of host immunity.Ticks represent one of the most important groups of anthropods, and transmit theileria parasites. To compare the tick salivary gland derived molecules among ticks distributed all over the world, molecular cloning of saliva derived molecules, such as calreticulin, a Ca<++>-binding multifunctional protein showing anti-complement and anti-thrombin antivities. In this study, the calreticulin gene from a tick species Rhipicephalus appendiculatus, which is a major vector of T. parva causing East coast fever in Africa was clearified. A calreticulin cDNA clone was obtained from a R. appendiculatus cDNA library by the 3' and 5' RACE methods. The mucleotide and deduced amino acid sequences of the calreticulin genes showed high homology with those of known calreticulin genes of other tick species, Amblyoma americanum and Boopiylus microplus. The expression of this gene is now under investigation.Next, we examined the molecular cloning of serine proteinase inhibitors (serpins). Serpins are known to regulate important functions in maintenance of homeostasis, such as the blood coagulation cascade, fibrinolysis, food digestion and fertilization. Three and 4 serpin cDNAs were obtained from H. longicornis and R. appendiculatus cDNA libraries, respectively. These clones showed high homology with known serpin genes of other ticks or mammalian species. Expression of these genes in E. coli and examination of biological activities are now under investigation.