Multigenic Family Analysis among the Encephalitozoon Genus

Encephalitozoon cuniculi is a parasite presenting a wide range of hosts among mammals (including human). Bioinformatic analysis of the genome sequence (11 chromosomes for a haploid genome size of 2.9 Mbp) revealed the presence of multigenic families in a subterminal position on the chromosomes (in 5′ of the rDNA copies on 22 extremities). One of these families was called InterB and clustered together about 30 genes within 10 homology groups. According to the predictions, the typical InterB protein presents in its N-terminal part a signal peptide, followed by two transmembrane domains. The core of this protein is characterized by an α hypervariable region rich in glutamine and lysine. The C-terminal region presents several conserved motifs (GGAR, YHL and FQI). A set of specific and generic oligonucleotides was designed to study the InterB genomic repertoire. The migration profile of the generic primers PCR products presents five to six bands. This profile is well conserved for the E. cuniculi isolates as well as for the different Encephalitozoon species. Some polymorphism is evident with amplicons of 300 bp in average. Sequence analysis revealed a higher level of polymorphism, especially in the α region. The InterB repertoire of transcripts was studied by reverse transcription. All InterB genes should be transcribed. There is no known homologue for InterB but, considering the position of the genes, we speculate on the possible role of InterB proteins. Similar multigenic family organizations have been described for proteins involved in pathogenicity of parasites such as Trypanosoma, Plasmodium, Giardia or Pneumocysti.