One of most common hallmarks of retrocopies (usually intronless RNA-based duplicates created from multi-exon parental genes through reverse transcription) is chromosomal gene movement, so situation in which retrocopy is located in a completely different genomic surrounding than a source gene. Number of previous studies showed a strong tendency for retrocopies to „escape” from chromosome X after retroposition, probably in order to avoid meiotic sex chromosome inactivation.
Here we examined, using bioinformatics and statistics methods, movement pattern for retrocopies in 15 animal genomes collected in RetrogeneDB (http://retrogenedb.amu.edu.pl). However, we used slightly different approach to these analyses because we decided to follow changes in localisation for each chromosome separately, not only for basic groups (all autosomes vs. chromosome X etc.). What is more, we analysed the pattern for all, as well as for expressed retrocopies only (according to our RNA-seq data analysis).
Our findings showed that chromosome X is on the top of the list of donor but for expressed retrocopies only for five species, while for majority of organisms retrocopies originated from one of the autosomes (i.e. chromosome 13 for human, 11 for marmoset, 6 for gorilla or 19 for chimp). Considering chromosomes that accept all retrocopies, for twelve species chromosome X presents maximum excess value, so there is visible trend for moving from automosome to sex chromosome. Only for human (chr 19), marmoset (chr 18), gorilla (chr 19) autosomes tend to gain more retrosequences. For expressed retrocopies, observed proportions are equal. We also tried to find if there are any factors describing those chromosomes served as donors or acceptors, especially for human.
Summing up, thanks to our approach, we can follow movement of retrocopies in details and observe differences related to expression pattern. Our results present an interesting perspective and will help to understand retroposition and it’s evolutionary consequences better.