Toxoplasma gondii Subtelomeres: Gene Composition, Adaptation and Non-Coding RNAs

ANGEL SO

Conferencia; 3rd Global Virtual Symposium on Toxoplasmosis; 2023

United Scientific Group

Toxoplasma gondii is a protozoan parasite which its success in worldwide distribution is based on its high capacity to adapt to different mammals and bird species and cellular environments. T. gondii is capable of sensing different environments and responding by changing its gene expression program and modifying its metabolism, replication, differentiation, etc.. Subtelomeres (ST) are poor-gene chromosome regions that separate telomeres from euchromatin and play relevant roles in chromatin modulation, DNA replication and genome stability. While their functions are conserved, ST structure and genetic compositions are unique to each species. ST genes are subject to dynamic evolution and associated with environmental stress, metabolic pathways, pathogenicity and virulence. STs were defined at chromosome ends based on poor gene density in the 13 T. gondii chromosomes. The length of STs ranges from 8.1 to 232.4 kbp, with a gene density of 0.049 genes/kbp, lower than Me49 genome (0.15/kbp). Chromatin organization showed that H3K9me3, H2A.X and H3.3 are highly enriched near telomere and 5’ end of silenced genes, decaying in intensity towards euchromatin. H3K4me3 and H2A.Z/H2B.Z are shown to be enriched in the 5´ end of the active ST genes. Satellite DNA was detected in almost all STs, mainly the ST sat350 and sat240 families. Within STs, there were 12 functional annotated genes, 59 with unknown function (Hypothetical proteins, HP), 15 multigene FamB and 13 multigene family FamC. Some genes presented low interstrain synteny associated to the presence of satellite DNA. Orthologues of FamB and FamC were also detected only in Neospora caninum and Hammondia hammondi. A re-analysis of different previous transcriptomic data indicated that ST genes expression is strongly linked to the adaptation to different situations such as extracellular passage (Evolve and resequencing study) and changes in metabolism (lack of acetyl-CoA cofactor). Genes associated to environmental response include HP, FamB and FamC families. FamB and FamC present a similar basic gene structure, code for integral membrane proteins with conserved and variable regions, in some cases with repeated motifs, but they are not evolutionarily related. T. gondii FamC is associated to a conserved 15-Kpb DNA fragment and almost all of FamC genes show evidence of transcription by RT-PCR. Antibodies against FamC rTgC8 recombinant protein detected a 49-kDa band in T. gondii lysate. TgC8 is localized at apical region of T. gondii although attempts for overexpression failed. rTgC8 and rTgC6 reacted poorly with serum from mice experimentally infected and T. gondii-infected individuals. In addition to gene-associated mRNAS, transcripts exist along ST in gene-free regions. A detailed study indicates that these could be putative lncRNAs. In conclusion, the ST region of the T. gondii chromosomes was defined, the STs genes were determined, and it was possible to associate them with a high interstrain plasticity and a role in the adaptability of T. gondii to environmental changes. The identity and function of these genes as well as the putative lncRNAs could yield new functions for the T. gondii STs.