Poster abstracts

Poster number 40 submitted by Nicholas Arredondo

Trans-spliced Leader Sequences Present a Novel Evolutionary Target of the DM15 Region of LARP1

Nicholas Arredondo (Department of Biological Sciences; University of Pittsburgh), Andrea Berman (Department of Biological Sciences; University of Pittsburgh)

The RNA-binding protein La-related protein 1 (LARP1) is present in most eukaryotes. In vertebrates, LARP1 regulates the translation of the mRNAs that encode the translation machinery. These mRNAs are characterized by a 5’ terminal oligopyrimidine (TOP) motif, which is directly bound by the LARP1 DM15 domain to repress their translation in response to mTOR kinase signaling inhibition. Interestingly, lower eukaryotes including the cnidarian Hydra also have LARP1 and TOR kinase signaling but lack TOP mRNAs. What is the target of the LARP1 DM15 region in organisms that lack TOP mRNAs?

The DM15 region is well conserved throughout evolution, especially along its RNA-binding surface. Because of this, we expect the LARP1 targets in Hydra have sequence and structural similarities to the TOP motif. Many Hydra mRNAs undergo a posttranscriptional processing called spliced leader (SL)-based trans-splicing. This phenomenon exists in many lower eukaryotes, in part, to post-transcriptionally resolve polycistronic pre-mRNAs into individual mRNAs. In this process, an SL sequence containing a m2,2,7G-trimethylated (TMG) cap is appended to the 5’ end of an mRNA. Similar to TOP motifs, SL sequences are pyrimidine rich. Therefore, we hypothesize that this TMG-capped SL sequence represents a potential motif for LARP1-directed translation regulation of these transcripts. Preliminary data demonstrates that the LARP1 DM15 region from cnidarian Styllophora pistallata directly and specifically binds an SL sequence, and likely associates with the TMG cap. Interestingly, in a chordate that undergoes SL-based trans-splicing, the translational regulation of SL-associated transcripts is controlled by TOR signaling (Danks, 2019). It has also been shown that in regenerative flatworms, 85% of their neoblast (stem cell) genes are trans-spliced. Neoblast proliferation and differentiation are responsible for the bulk of flatworm regeneration. Therefore, this study aims to elucidate the molecular mechanism by which these transcripts are regulated. Results from this study could also implicate LARP1’s differential binding ability in the regenerative capacities of lower eukaryotes.

Keywords: Trans-splicing, LARP, RBP