Abstract
Characteristics of trans-splicing in Schistosoma mansoni were examined to explore the significance and determinants of spliced leader (SL) addition in flatworms. Only a small subset of mRNAs acquire the SL. Analysis of 30 trans-spliced mRNAs and four genes revealed no discernable patterns or common characteristics in the genes, mRNAs, or their encoded proteins that might explain the functional significance of SL addition. While the mRNA encoding the glycolytic enzyme enolase is trans-spliced, mRNAs encoding four other glycolytic enzymes are not, indicating trans-splicing is not prevalent throughout this metabolic pathway. Although the 3' end of flatworm SLs contribute an AUG to mRNAs, the SL AUG does not typically serve to provide a methionine for translation initiation of reading frames in recipient mRNAs. SL RNA expression exhibits no apparent sex, tissue, or cell specificity. Trans-spliced genes undergo both cis- and trans-splicing, and the sequence contexts for these respective acceptor sites are very similar. These results suggest trans-splicing in flatworms is most likely associated either with some property conferred on recipient mRNAs by SL addition or related to some characteristic of the primary transcripts or transcription of trans-spliced genes.
Highlights
Characteristics of trans-splicing in Schistosoma mansoni were examined to explore the significance and determinants of spliced leader (SL) addition in flatworms
These results suggest trans-splicing in flatworms is most likely associated either with some property conferred on recipient mRNAs by SL addition or related to some characteristic of the primary transcripts or transcription of trans-spliced genes
Available evidence suggests that a low percentage of schistosome mRNAs are transspliced based on the following: 1) only one of five glycolytic mRNAs we examined is trans-spliced, 2) the frequency of trans-splicing among mRNAs and their genes whose ends have been characterized and reported in the literature or data bases, 3) analysis of several types of schistosome cDNA
Summary
Characteristics of trans-splicing in Schistosoma mansoni were examined to explore the significance and determinants of spliced leader (SL) addition in flatworms. Trans-spliced genes undergo both cis- and trans-splicing, and the sequence contexts for these respective acceptor sites are very similar. These results suggest trans-splicing in flatworms is most likely associated either with some property conferred on recipient mRNAs by SL addition or related to some characteristic of the primary transcripts or transcription of trans-spliced genes. In one form of trans-splicing, a leader sequence (the spliced leader, SL) is donated from the 59 end of a small, non-polyadenylated RNA (the spliced leader RNA, SL RNA) to pre-mRNAs to form the 59-terminal exon of mature mRNAs This form of RNA maturation was first described in trypanosomes [7, 8] and subsequently in other kinetoplastida and the flagellated protozoan Euglena [9]
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