Telomeric Heterochromatin inPlasmodium falciparum

Abstract

Until very recently, little was known about the chromatin structure of the telomeres and subtelomeric regions in Plasmodium falciparum. In yeast and Drosophila melanogaster, chromatin structure has long been known to be an important aspect in the regulation and functioning of these regions. Telomeres and subtelomeric regions are enriched in epigenetic marks that are specific to heterochromatin, such as methylation of lysine 9 of histone H3 and lysine 20 of histone H4. In P. falciparum, histone modifications and the presence of both the heterochromatin “writing” (PfSir2, PKMT) and “reading” (PfHP1) machinery at telomeric and subtelomeric regions indicate that these regions are likely to have heterochromatic structure that is epigenetically regulated. This structure may be important for telomere functions such as the silencing of the var gene family implicated in the cytoadherence and antigenic variation of these parasites.

Analysis of the spatial and temporal arrangement of transcripts over intergenic regions in the human malarial parasite Plasmodium falciparum

“…falciparum chromosomes are typically divided into subtelomeric and chromosome-internal domains; reflecting their differing heterochromatic environment, multigene family composition, sub-nuclear organization and length plasticity [3,9,40-45]. Whilst we know there is a reduced gene density within subtelomeric regions, whether this is reflected in differences in the size and orientation of IGR is not known.…”

Characterization of Toxoplasma gondii subtelomeric-like regions: identification of a long-range compositional bias that is also associated with gene-poor regions

“…These are sets of genes responsible for pathogen diversity and for the clonal phenotype switches often associated with the parasite’s escape from the host immune system. In the Apicomplexan parasite P. falciparum , chromosome ends consist of the telomeric repeat (T(G/A)AAGGG)n followed by a telomere-associated repetitive elements (TARE1-6) organized in six blocks flanked with the members of the var, stevor and rif multi-gene families responsible for the antigenic variation and cytoadhesion [ 27 – 29 ]. TASs in this parasite also present a specialized chromatin, different from the rest of the genome, rich in nucleosomes containing H3K9me3 and the histone deacetylase PfSir2 [ 30 , 31 ].…”

Basidiomycetes Telomeres – A Bioinformatics Approach

“…The genome of P. falciparum is organized in 14 compartmentalized chromosomes where the conserved regions form the central chromosomal domains and the polymorphic regions are at the terminal domains. In this way, housekeeping genes tend to be located at the central regions of the chromosomes, whereas the highly variable gene families responsible for the antigenic variation of the parasite are clustered towards the telomeres (Hernandez-Rivas et al, 2010). Our results suggest that a similar type of chromosomal organization would be expected to occur in basidiomycetes, although a larger number of genomes should be studied to fully support this hypothesis.…”

“…Heterochromatin has been often said to be "poor in genes" and mainly constituted by repetitive DNA sequences. Moreover, since it is highly condensed and inaccessible to transcription factors, heterochromatin is generally transcriptionally silent (Hernandez-Rivas et al, 2010). Heterochromatin appears as blocks spread over the chromosomes when they are stained with Giemsa dye.…”