Abstract
Transfer RNA (tRNA)-derived small RNAs (tsRNAs) are newly identified non-coding small RNAs that have recently attracted attention due to their functional significance in both prokaryotes and eukaryotes. tsRNAs originated from the cleavage of precursor or mature tRNAs by specific nucleases. According to the start and end sites, tsRNAs can be broadly divided into tRNA halves (31–40 nucleotides) and tRNA-derived fragments (tRFs, 14–30 nucleotides). tsRNAs have been reported in multiple organisms to be involved in gene expression regulation, protein synthesis, and signal transduction. As a novel regulator, tsRNAs have also been identified in various protozoan parasites. The conserved biogenesis of tsRNAs in early-branching eukaryotes strongly suggests the universality of this machinery, which requires future research on their shared and potentially disparate biological functions. Here, we reviewed the recent studies of tsRNAs in several representative protozoan parasites including their biogenesis and the roles in parasite biology and intercellular communication. Furthermore, we discussed the remaining questions and potential future works for tsRNAs in this group of organisms.
Highlights
Transfer RNAs are essential adaptor molecules used to translate the information from nucleic acid to peptides and are highly conserved in all three domains of life. tRNAs can be distinguished from other RNAs by their unique characteristics, namely: (1) tRNAs have short sequences of 70–100 nucleotides, and are folded into a highly conserved cloverleaf secondary structure and an L-shaped tertiary structure [1], and (2) tRNAs are heavily modified at up to 20% of their nucleotides [2], which can prevent tRNA degradation [3] and affect amino acid charging [4,5] and protein biosynthesis [6]. tRNAs undergo several steps of posttranscriptional processing of the precursor tRNA transcript
Recent developments in unbiased high-throughput sequencing facilitated the discovery of a new class of non-coding RNA, tRNA-derived small RNAs, which map to the known tRNA genes [8–10]
The biological functions of tRNA-derived small RNAs (tsRNAs) in representative protozoan parasites have been linked to the regulation of cellular differentiation, stress response, and parasite-parasite or parasite-host interaction by fundamental mechanisms of: (a) tsRNAs export via extracellular vesicles to communicate to other parasites or to host cells leading to a variety of downstream phenotypic changes, (b) tsRNAs interact with ribosome and affect protein synthesis reported in Trypanosoma brucei
Summary
Transfer RNAs (tRNAs) are essential adaptor molecules used to translate the information from nucleic acid to peptides and are highly conserved in all three domains of life. tRNAs can be distinguished from other RNAs by their unique characteristics, namely: (1) tRNAs have short sequences of 70–100 nucleotides, and are folded into a highly conserved cloverleaf secondary structure and an L-shaped tertiary structure [1], and (2) tRNAs are heavily modified at up to 20% of their nucleotides [2], which can prevent tRNA degradation [3] and affect amino acid charging [4,5] and protein biosynthesis [6]. tRNAs undergo several steps of posttranscriptional processing of the precursor tRNA transcript. TRNA halves originate from a single cleavage at the anticodon loop of mature tRNAs and this process was first demonstrated under cellular stress condition catalyzed by angiogenin (ANG) [17]. They can be further classified as either 5 tRNA halves or 3 tRNA halves with a length range of 31 to 40 nucleotides [16]. At least two other classes of tRFs, (e) tRNA intronic circular RNA (tricRNA) synthesized from intron-containing tRNAs during intron splicing [19] and (f) 5 external transcribed spacer (ETS) and internal transcribed spacer (ITS) present in prokaryotic precursor tRNAs [15,20] (will not be discussed here), have been reported.
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