The mutational load in natural populations is significantly affected by high primary rates of retroposition

Abstract

Gene retroposition is known to contribute to patterns of gene evolution and adaptations. However, possible negative effects of gene retroposition remain largely unexplored, since most previous studies have focussed on between-species comparisons where negatively selected copies are mostly not observed, as they are quickly lost from the populations. Here, we show for natural house mouse populations that the primary rate of retroposition is orders of magnitude higher than previously thought. Comparisons with SNP distribution patterns in the same populations show that most retroposition events are deleterious. Transcriptomic profiling analysis shows that new retroposed copies become easily subject to transcription and have an influence on the expression level of their parental genes, especially when transcribed in the antisense direction. Our results imply that the impact of retroposition on the mutational load in natural populations has been highly underestimated, which has also implications for strategies of disease allele detection in humans. Significance statementThe phenomenon or retroposition (re-integration of reverse transcribed RNA into the genome), has been well studied in comparisons between genomes and has been identified as a source of evolutionary innovation. However, the negative effects of retroposition have been overlooked so far. Our study makes use of a unique population genomic dataset from natural mouse populations. It shows that the retroposition rate is magnitudes higher than previously suspected. We show that most of the newly transposed retrocopies have a deleterious impact through modifying the expression of their parental genes. In humans, this effect is expected to cause disease alleles and we propose that genetic screening needs to take into account the search for newly transposed retrocopies.