Long terminal repeat (LTR) retrotransposons are a widespread
kind of transposable element present in eukaryotic genomes. They
are a major factor in genome evolution due to their ability to
create large scale mutations and genome rearrangements. Compared
to other transposable elements, little attention has been paid
to elements belonging to the metazoan BEL/Pao subclass of LTR
retrotransposons. No comprehensive characterization of these
elements is available so far. The aim of this study was to
describe all BEL/Pao elements in a set of 62 sequenced metazoan
genomes, and to analyze their phylogenetic relationship. We
identified a total of 7,861 BEL/Pao elements in 53 of our 62
study genomes. We identified BEL/Pao elements in 20 genomes
where such elements had not been found so far. Our analysis
shows that BEL/Pao elements are the second-most abundant class
of LTR retrotransposons in the genomes we study, more abundant
than Ty1/Copia elements, and second only to Ty3/Gypsy elements.
They occur in multiple phyla,