Publication Date:
2015-02-14
Description:
Polycistronic mRNAs transcribed from operons are resolved via the trans -splicing of a spliced-leader (SL) RNA. Trans -splicing also occurs at monocistronic transcripts. The phlyogenetically sporadic appearance of trans -splicing and operons has made the driving force(s) for their evolution in metazoans unclear. Previous work has proposed that germline expression drives operon organization in Caenorhabditis elegans , and a recent hypothesis proposes that operons provide an evolutionary advantage via the conservation of transcriptional machinery during recovery from growth arrested states. Using a modified cap analysis of gene expression protocol we mapped sites of SL trans -splicing genome-wide in the marine chordate Oikopleura dioica . Tiled microarrays revealed the expression dynamics of trans -spliced genes across development and during recovery from growth arrest. Operons did not facilitate recovery from growth arrest in O. dioica . Instead, we found that trans -spliced transcripts were predominantly maternal. We then analyzed data from C. elegans and Ciona intestinalis and found that an enrichment of trans -splicing and operon gene expression in maternal mRNA is shared between all three species, suggesting that this may be a driving force for operon evolution in metazoans. Furthermore, we found that the majority of known terminal oligopyrimidine (TOP) mRNAs are trans -spliced in O. dioica and that the SL contains a TOP-like motif. This suggests that the SL in O. dioica confers nutrient-dependent translational control to trans -spliced mRNAs via the TOR-signaling pathway. We hypothesize that SL- trans -splicing provides an evolutionary advantage in species that depend on translational control for regulating early embryogenesis, growth and oocyte production in response to nutrient levels.
Print ISSN:
0737-4038
Electronic ISSN:
1537-1719
Topics:
Biology
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