Internal initiation of reverse transcription in a Penelope-like retrotransposon
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The paper presents an exciting new discovery about Penelope-like elements (PLEs), which are a class of retrotransposons that are distinct from the long-terminal repeat (LTR) retrotransposons. The key finding is that the PLE from Anolis carolinensis (the green anole lizard) is able to mobilize via a unique mechanism of reverse transcription that is different from the LTR retrotransposons.
The main evidence for this finding comes from the in vitro characterization of the PLE from Anolis carolinmaculate. The authors expressed the PLE protein in E. coli under conditions that allowed for proper folding of the protein. Using purified and folded PLE protein, as well as the associated reverse transcriptase, they performed in vitro assays to study the mechanism of transposition of this element. They found that the PLE is able to mobilize via a novel reverse transcription mechanism.
The key finding is that the PLE utilizes a novel type of reverse transcription that is different from the canonical reverse transcription that occurs with LTR retrotransposons. Specifically, the PLE utilizes a type of reverse transcription that requires a "seed" nucleotide to initiate reverse transcription. This was demonstrated through the identification of point mutations that knock out the activity of this PLE element.
Typically, LTR retrotransposons utilize reverse transcription mediated by an enzyme called reverse transcriptase, which is encoded by the virus upon infection. However, in the case of this PLE from Anolis carolinensis, the mechanism of reverse transcription is different and is mediated by a different enzyme that is encoded by the host genome. Furthermore, this enzyme uses self-tryptophan
Self-tryptophan is a natural amino acid found in green anoles. Overall, the PLE is able to utilize the host's machinery for reverse transcription, which is very different from the LTR retrotransposons.
This finding is significant because it gives insight into the evolution of the machinery required for mobilization of these elements. The fact that the PLE can utilize the protein machinery from the host genome indicates that the host has developed a specific mechanism for mobilization of these elements. This is in contrast with the LTR retrotransposons such as the majority of the NCTR elements. As such, the host has evolved a specific machinery to make both the virus and the host factors required for mobilization in a concerted way.
This insight can help to better understand the evolution of genetic novelty and novelty of host factors. The machinery required for mobilization of host factors indicates that the host was able to produce the host factors required for mobilization of genetic novelty through mutations to host proteins.
There are some additional potential insights and implications from this paper:
This finding demonstrates that the green anole has evolved a competent mechanism for the mobilization of genetic novelty through genetic changes to allow mobilization of genetic novelty from the host genome. This indicates that the mobilization of genetic novelty from the host genome arose due to a genetic adaptation in the host organism.
The fact that the LincRNA machinery is involved in mobilization indicates that this mechanism arose in a common ancestor of the insect lineage, as the machinery is involved in the mobilization of factors encoded from the linx53 element that covers the insect genomes. This suggests that the ancestors of the insect lineage such as ascomycetes may have played a role in the spread of this mechanism across insect genomes and played a role in the origin of this mechanism.
The fact that the mobilization machinery involved tryptophan as the host factor indicates that its spread across insect genomes may have been mediated by the spread of tryptophan utilization in those genomes. Some insect phytopaths are known to utilize tryptophan for virulence. If the origin of the machinery emerged in the insect ancestors, it may have emerged from an associated tryptophan utilization mechanism.
The ability to produce genetic novelty from the host genome may have played a role in the ability of the host to rapidly adapt to novel environments and environments with specific challenges. For example, if specific stress challenges must be overcome, the ability to produce genetic novelty could allow the host to adapt more efficiently. If specific challenges must be overcome, such as heat/cold stress, Phytophthora/fungi/bacterial infections, the ability to produce genetic novelty may allow the host to adapt more efficiently.
Overall, this paper presents an exciting discovery about the novel mechanism of mobilization of genetic novelty from the host genome. This discovery has important implications for understanding the origins of genetic novelty and adaptation, as well as its spread and evolution across species. The finding provides insights into how machinery for genetic mobility spreads across the genomes and how genetic novelty enables adaptation to specific environments through mutations, horizontal transfer and mobility of genetic novelty.
https://link.springer.com/article/10.1186/s13100-024-00322-z
