Abstract
Telomerase RNAs (TERs) are highly divergent between species, varying in size and sequence composition. Here, we identify a candidate for the telomerase RNA component of Leishmania genus, which includes species that cause leishmaniasis, a neglected tropical disease. Merging a thorough computational screening combined with RNA-seq evidence, we mapped a non-coding RNA gene localized in a syntenic locus on chromosome 25 of five Leishmania species that shares partial synteny with both Trypanosoma brucei TER locus and a putative TER candidate-containing locus of Crithidia fasciculata. Using target-driven molecular biology approaches, we detected a ∼2,100 nt transcript (LeishTER) that contains a 5′ spliced leader (SL) cap, a putative 3′ polyA tail and a predicted C/D box snoRNA domain. LeishTER is expressed at similar levels in the logarithmic and stationary growth phases of promastigote forms. A 5′SL capped LeishTER co-immunoprecipitated and co-localized with the telomerase protein component (TERT) in a cell cycle-dependent manner. Prediction of its secondary structure strongly suggests the existence of a bona fide single-stranded template sequence and a conserved C[U/C]GUCA motif-containing helix II, representing the template boundary element. This study paves the way for further investigations on the biogenesis of parasite TERT ribonucleoproteins (RNPs) and its role in parasite telomere biology.
Highlights
Leishmania spp. are trypanosomatid protozoa, considered ancient eukaryotes whose nuclear genome is organized in linear chromosomes [1,2]
Leishmania telomeres are formed by conserved 59-TTAGGG-39 telomeric repeats that typically end in a 39 overhang that serves as substrate for repeat addition by telomerase [3,4,5,6], a ribonucleoprotein enzyme minimally composed of two catalytically essential subunits: the telomerase reverse transcriptase protein (TERT) and the telomerase RNA (TER) component, which contains the template that specifies the sequence of the telomeric repeats [7,8]
LmjF.25.0870 is orthologous to Tb927.11.0850, which is the second gene downstream of the TER locus in T. brucei, so we explored the synteny surrounding the putative TER locus in the genomes of three different trypanosomatid genera by using the ACT tool [26] to visualize tBLASTx comparisons of chr25 from L. major and L. mexicana, chr28 from Crithidia fasciculata and chr11 from T. brucei (Figure 1)
Summary
Leishmania spp. are trypanosomatid protozoa, considered ancient eukaryotes whose nuclear genome is organized in linear chromosomes [1,2]. Like most eukaryotes, their chromosomes end termini are characterized by sequences known as telomeres [3]. Leishmania telomeres are formed by conserved 59-TTAGGG-39 telomeric repeats that typically end in a 39 overhang that serves as substrate for repeat addition by telomerase [3,4,5,6], a ribonucleoprotein enzyme minimally composed of two catalytically essential subunits: the telomerase reverse transcriptase protein (TERT) and the telomerase RNA (TER) component, which contains the template that specifies the sequence of the telomeric repeats [7,8].
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