A comprehensive analysis of the Baboon-specific full-length LINE-1 retrotransposons

Long interspersed elements-1 (LINE-1s or L1s) and Alu elements are most successful retrotransposons that have generated genetic diversity and genomic fluidity in the primate genome. They account for ~ 27.7% of the primate genome. Interestingly, a previous study has shown that the retrotransposition rate of Alu elements is nine times higher in baboons than in humans.

The expansion of Alu copies could be dependent on the activity of L1-encoded proteins. Thus, we aimed to investigate full-length baboon-specific L1s and characterize structurally and functionally intact baboon-specific L1s (ORF1p/ORF2p and ORF2p only) that could induce trans-mobilization of Alu elements in the baboon genome.

A total of 673 baboon-specific L1 candidates (> 4 kb) were identified through the comparative genomic analysis. Applying the baboon-specific correction value obtained from the experimental validation, it demonstrated that approximately 446 baboon-specific L1s (> 4 kb) were present in the baboon reference genome (papAnu2). In addition, we observed phylogenetic relationship of the baboon-specific L1s through the neighbor-joining method and they diverged from the L1PA6 consensus sequence. Finally, we identified 36 full-length baboon-specific L1s that were intact both ORF1p and ORF2p.

The number of baboon-specific full-length L1s is fewer than the number of human-specific full-length L1s. Therefore, there is possibility that the "L1 master gene" or "L1 source gene" is more abundant in the baboon genome, or that in trans retrotransposition activity of baboon-specific L1s is relatively stronger than in the other genomes.