GENETIC-ANALYSIS IN TOXOPLASMA - GENE DISCOVERY WITH EXPRESSED SEQUENCE TAGS AND RAPID MAPPING OF NATURAL POLYMORPHISMS

Genetic analysis of the protozoan parasite Toxoplasma gondii has under gone a rapid expansion in recent years. This is due to effort in a num ber of laboratories that have worked on the development of molecular g enetic techniques. It is also due, however, to the natural biology of this system (including a well-described sexual cycle) that makes possi ble genetic mapping of the F-1 progeny from a cross. In this article, we present a detailed methodology for rapidly mapping natural polymorp hisms between the ME49 and CEP strains for which extensive restriction fragment length polymorphism analysis has already been performed. The example we present shows that the failure to detect expression of bra dyzoite-specific surface antigens in the CEP strain under conditions t hat promote differentiation in vitro is not a result of a general fail ure to express such genes; instead, it is apparently due to antigenic polymorphism in the gene products concerned, This conclusion was reach ed rapidly and definitively by genetic mapping, whereas molecular appr oaches would have taken considerably longer, We also show how the rece nt effort to create an extensive database of expressed sequence tags f or this parasite can promote the very rapid discovery of genes that re veal much about the biology of Toxoplasma. The example presented deals with the expression of a family of closely related surface antigens i n the tachyzoite stage. (C) 1997 Academic Press.