Species-Specific Duplication of Surface Antigen Genes in Paramecium

Abstract

Paramecium is a free-living ciliate that undergoes antigenic variation and still the functions of these variable surface antigen coats in this non-pathogenic ciliate remain elusive. Only a few surface antigen genes have been described, mainly in the two model species P. tetraurelia strain 51 and P. primaurelia strain 156. Given the lack of suitable sequence data to allow for phylogenetics and deeper sequence comparisons, we screened the genomes of six different Paramecium species for serotype genes and isolated 548 candidates. Our approach identified the subfamilies of the isogenes of individual serotypes that were mostly represented by intrachromosomal gene duplicates. These showed different duplication levels, and chromosome synteny suggested rather young duplication events after the emergence of the P. aurelia species complex, indicating a rapid evolution of surface antigen genes. We were able to identify the different subfamilies of the surface antigen genes with internal tandem repeats, which showed consensus motifs across species. The individual isogene families showed additional consensus motifs, indicating that the selection pressure holds individual amino acids constant in these repeats. This may be a hint of the receptor function of these antigens rather than a presentation of random epitopes, generating the variability of these surface molecules.

A Review for the Special Issue on Paramecium as a Modern Model Organism

“…In P. caudatum, this immature period lasts for about 50 fissions. Using the important technique of microinjection, Haga and Hiwatashi [70] identified a cytoplasmic factor that inhibits mating by mature cells. From the cytoplasm used to inhibit mating, Haga and Hiwatashi isolated a small protein they called immaturin.…”

“…From the cytoplasm used to inhibit mating, Haga and Hiwatashi isolated a small protein they called immaturin. P. caudatum cells age and, when they reach senescence, are unable to mate [70]. Immaturin also has the property of reversing senility in aging cells.…”