Removal of beneficial insertion effects prevent the long-term persistence of transposable elements within simulated asexual populations

摘要

Transposable elements (TEs) are short regions of non-coding DNA (100-10,000 bp) which can proliferate throughout a genome, and are significant genomic components of a taxonomically diverse range of species [1–3]. Understanding the processes which drive TE variation across different species is an important goal in answering the so-called ‘C-value’ paradox (the observed lack of relationship between genome size and organismal complexity) [4]. TEs are thought to accumulate within a population through a number of evolutionary mechanisms which include (i) positive selection, (ii) genetic drift, (iii) co-evolution with the host, (iv) sexual recombination or (v) horizontal transfer. Kremer et al. [5] investigated the fate of TE populations where none of these population genetic scenarios were possible [5]. Using in-silico modelling, the authors established an asexual population where (i) TE insertions had serious negative effects on host fitness, (ii) TEs could not evolve insertion site preferences (i.e. no co-evolution with the host) and (iii) TEs were not able to be horizontally transferred. Surprisingly, even in the absence of these evolutionary forces, TEs accumulated in a limited number (3%) of scenarios. The authors concluded that these rare accumulation events may be explained through ‘TE engineering’; a process in which the activity of TEs significantly alters the landscape of a genome to facilitate further proliferation. Specifically, they suggest that the cycle of TE proliferation and degradation may provide new non-coding regions in which future TEs can insert with little or no consequence on host fitness. Changes in TE abundance which occur through their interactions with either the host genome or other transposons comprise a poorly studied field known as ‘TE ecology’ [6, 7]. Consequently, Kremer et al. [5] appears to have identified a novel mechanism for TE proliferation, with important implications regarding our understanding of TE dynamics.