ANTIGENIC VARIATION IN TRYPANOSOMES - SECRETS SURFACE SLOWLY

Among pathogenic micro-organisms that evade the mammalian immune respo nses, Trypanosoma brucei has developed the most elaborate capacity for antigenic variation, Trypanosomes branched early during eukaryotic ev olution. They are characterized by many aberrations, ranging from the unusual compartmentation of metabolic pathways to the heresy of RNA ed iting. The ubiquitous phenomenon of glycosylphosphatidylinositol-ancho ring of eukaryotic plasma membrane proteins and RNA trans-splicing (tr ypanosome genes contain no introns), which adds an identical leader se quence to all trypanosome mRNAs, were first defined during studies of antigenic variation. Genetic transformation of trypanosomes and the hi gh efficiency of gene targeting provide new opportunities to investiga te the regulation of antigenic variation. There is every reason to exp ect trypanosomes to provide further surprises and insights into the ev olution of genetic regulatory mechanisms.