tSplit the TE-splitter

Extract terminal repeats from retrotransposons (LTRs) or DNA transposons (TIRs). Returns compontent segments of the element for use with transposon mapping tools.

Optionally, tsplit TIR can also compose synthetic MITES from complete DNA transposons.

Table of contents

• Algorithm overview
• Options and usage
  • Installing tSplit
  • Example usage

Algorithm overview

tSplit attempts to identify terminal repeats in transposable elements by first aligning each element to itself using blastn or nucmer, and then applying a set of tuneable heuristics to select an alignment pair most likely to represent an LTR or TIR, as follows:

1. Exclude all diagonal/self-matches
2. If tsplit LTR: Retain only alignment pairs on the same strand (tandem repeats)
3. If tsplit TIR: Retain only alignment pairs on opposite strands (inverse repeats)
4. Retain pairs for which the 5' match begins within x bases of element start and whose 3' match ends within x bases of element end
5. If multiple candidates remain select alignment pair with largest internal segment (i.e. closest to element ends)

Options and usage

Installing tSplit

Requirements:

• pymummer version >= 0.10.3 with wrapper for nucmer option --diagfactor.
• MUMmer
• BLAST+ (Optional)

Installation options:

```bash

Install from PyPi:

pip install tsplit

Clone and install latest dev version from this repository:

git clone https://github.com/Adamtaranto/tSplit.git && cd tSplit && pip install -e '.[dev]' ```

Example usage

tSplit can be run in two modes: tsplit LTR and tsplit TIR, for extracting long terminal repeats or terminal inverted repeats, respectively.

Options are the same for each.

tsplit TIR

For each element in TIR_element.fa split into internal and external (TIR) segments.

Split segments will be written to TIRsplittsplit_output.fasta with suffix "I" for internal or "TIR" for external segments.

TIRs must be at least 10bp in length and share 80% identity and occur within 10bp of each end of the input element.

Additionally, synthetic MITEs will be constructed by concatenation of left and right TIRs, with internal segments excised.

```bash tsplit TIR -i tests/data/TIRelement.fa -p TIRsplit --makemites --keeptemp

Equivalet to defaults

tsplit TIR -i tests/data/TIRelement.fa -p TIRsplit --maxdist 10 --minid 80.0 --minterm 10 --method blastn --splitmode split --makemites --keeptemp ```

Output: TIR_split_tsplit_output.fasta

tsplit LTR

For each element in LTR_retrotransposon.fa split into internal and external segments.

Split segments will be written to LTRsplittsplit_output.fasta with suffix "I" for internal or "LTR" for external segments.

LTRs must be at least 10bp in length and share 80% identity and occur within 10bp of each end of the input element.

bash tsplit LTR -i tests/data/LTR_retrotransposon.fa -p LTR_split

Output: LTRsplittsplit_output.fasta

License

Software provided under MIT license.