Analysis of chromosome conserved end regions (ChCERs) of Toxoplasma gondii.

DALMASSO MC; AGÜERO F; ANGEL SO

Mar del Plata

Congreso; IX Congreso Argentino de Protozoologia y Enfermedades Parasitarias; 2011

Sociedad Argentina de Protozoologia

BM. Analysis of Chromosome Conserved End Regions (ChCERs) of Toxoplasma gondii María Carolina Dalmasso, Fernán Agüero and Sergio Angel. IIB-INTECH, Cmo. Circunv. Laguna Km6, (7130) Chascomus, Buenos Aires Toxoplasma gondii is an Apicomplexan parasite that causes toxoplasmosis. This infectious disease is distributed worldwide and is particularly damaging to young children, immunocompromised patients, and unborn babies (through placental transmission). In many pathogens, a number of virulence genes are clustered at subtelomeric regions. It has been described that the chromosome ends of Plasmodium falciparum (Apicomplexa) have a non-coding region containing six Telomere Asociated Repetitive Elements (TAREs) and a coding region containing virulence genes. TAREs are involved in chromosome segregation, and clustering of telomeres at the nucleus periphery in order to facitlitate var gene rearrangements. In the T. gondii genomes currently available, telomeres are not completely assembled, and chromosome ends have not yet been analyzed. Moreover, no virulence gene clusters have been described at subtelomeric regions in this parasite. Therefore, our goal in this study was to analyze the presence of specific arrangements at chromosome ends in T. gondii. We started by performing an all-vs-all pairwise comparison of T. gondii chromosomes using ACT (http://www.sanger.ac.uk/Software/ACT). As a result we could observe the presence of a conserved? region of aproximately 25 to 30 Kbp that we denominated chromosome conserved end region (ChCER). ChCERs are present at the ends? of 10 of the 14 chromosomes of T. gondii, and show more than 65% identity among them. Subsequently, we compared each ChCER to each other using Dotter (http://sonnhammer.sbc.su.se/Dotter.html). With this tool we were able uncover a shared pattern in all these regions: a repetitive sequence (REP1) followed by a fragment of ~ 10 Kbp (Fragment A), and a second repetitive sequence (REP2) followed by other genomic fragment of ~ 10 Kpb (Fragment B). A detailed analysis of each ChCER using the ToxoDB - Genome Browser (http://toxodb.org/cgi-bin/gbrowse/toxodb/) suggested that these regions contain mostly silenced sequences, except for the presence of an hypothetical protein localized at the end of every Fragment B. These hypothetical proteins are annotated as members of the ´Toxoplasma specific family´ (TSF). All TSF genes are apparently transcribed (have associated EST and mRNA-seq data, and H3K9ac of H3K4me3 peaks that indicate the presence of an active promoter). However, there is currently no evidence of expression at the protein level for any of them (mass spectrometry evidence at ToxoDB). ChCERs are specific for T. gondii and are syntenic in the three strains analyzed (ME49, VEG and GT1) with more than 98% identity among strains. These results demonstrate the presence of specific patterns in the chromosome ends of T. gondii, that might be important for the parasite biology.