In this chapter, we focus on the structure and function of telomeres and
subtelomeres of human protozoan parasites T. cruzi, T. rangeli and Leishmania spp..
Beyond their role in maintaining the integrity of chromosomes, telomeres and
subtelomeres are involved in the survival mechanisms of these single-celled parasites.
The telomeric repeat (5'-TTAGGG-3')n is conserved among trypanosomatid species, but
adjacent subtelomers vary between species and chromosomes within the same cell. The
chromosome ends of T. rangeli, for example, exhibit a simple organization with short
subtelomeres whereas T. cruzi subtelomeres are a complex mosaic of genomic
fragments including gene/pseudogenes corresponding to large gene families of surface
proteins and retrotransposons. Differences in the copy number and organization of
these genes determine the variation in the size of subtelomeres on each T. cruzi
chromosome. Leishmania subtelomeres, in contrast, lack genes encoding surface
antigens; instead they carry conserved repeat sequences referred to as telomereassociated
sequences. T. cruzi and T. rangeli chromosomes share a high level of
synteny which is lost in the subtelomeric regions. It has been suggested that T. cruzi
subtelomeres can serve as recombination hotspots and thus promoting the increase of
the repertoire of surface antigens. Many pieces of evidence indicate that telomere
maintenance in Kinetoplastids occurs primarily by a telomerase-mediated elongation. The catalytic subunit of telomerase (TERT) is present in all sequenced trypanosomatid
species, whereas the RNA component containing a template for telomere repeat
extension has recently been identified in T. brucei and Leishmania. Further studies are
needed to understanding the regulation of telomere homeostasis and the biology of
subtelomeres of trypanosomatids.
Keywords: Base modification, Chromosomes ends, Contingency genes,
Retrotransposons, Subtelomere, Surface protein genes, Telomerase, Telomere
generation, Telomere junction, Telomere repeats.
