Horizontal Transfer of Non-LTR Retrotransposons

<p>Horizontal transfer is a complex phenomenon usually used as explanation of phylogenetic inconsistence which can not be interpreted in terms of vertical evolution. Most examples of horizontal transfer of eukaryotic genes involve transposable elements. An intriguing feature of horizontal transfer is that its frequency differs among transposable elements classes. Although horizontal transfer is well known for DNA transposons and LTR retrotransposons, majority of previously described cases of horizontal transfer for non-LTR retrotransposons were dismissed based on the analysis of non-LTR retrotransposon sequence change rates. Nevertheless, recent findings suggest that non-LTR retrotransposons can be horizontally transmitted. Thus, one cannot completely exclude the possibility of horizontal transfer for this group of transposable elements. We review the occurrence of horizontal transfer of non-LTR retrotransposons and examine the criteria used to infer such transfers.</p>