Differential L1 regulation in pluripotent stem cells of humans and apes

Abstract

Induced pluripotent stem-cell characterization reveals phenotypical differences between humans and non-human primates (NHPs): gene expression analysis shows differences in the regulation of long interspersed element-1 (L1) transposons, and in the expression of L1-restricting genes APOBEC3B and PIWIL2, correlating with higher L1 mobility in NHPs; this indicates that L1 mobility differences may have differentially shaped the human and NHP genomes. This paper reports the derivation and characterization of induced pluripotent stem (iPS) cells from chimpanzees and bonobos, and the use of the resulting iPS cells to study phenotypical differences between human and non-human primates (NHPs). Comparative gene expression analysis reveals greater expression of long interspersed element-1 (L1) in chimpanzees and bonobos than in humans. Differential expression of two genes (APOBEC3B and PIWIL2) between humans and the NHPs correlates with L1 transposon mobility and endogenous L1 messenger RNA levels. The authors propose that differences in L1 mobility may have differentially shaped the genomes of humans and NHPs and could have ongoing adaptive significance. Identifying cellular and molecular differences between human and non-human primates (NHPs) is essential to the basic understanding of the evolution and diversity of our own species. Until now, preserved tissues have been the main source for most comparative studies between humans, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus)1,2. However, these tissue samples do not fairly represent the distinctive traits of live cell behaviour and are not amenable to genetic manipulation. We propose that induced pluripotent stem (iPS) cells could be a unique biological resource to determine relevant phenotypical differences between human and NHPs, and that those differences could have potential adaptation and speciation value. Here we describe the generation and initial characterization of iPS cells from chimpanzees and bonobos as new tools to explore factors that may have contributed to great ape evolution. Comparative gene expression analysis of human and NHP iPS cells revealed differences in the regulation of long interspersed element-1 (L1, also known as LINE-1) transposons. A force of change in mammalian evolution, L1 elements are retrotransposons that have remained active during primate evolution3,4,5. Decreased levels of L1-restricting factors APOBEC3B (also known as A3B)6 and PIWIL2 (ref. 7) in NHP iPS cells correlated with increased L1 mobility and endogenous L1 messenger RNA levels. Moreover, results from the manipulation of A3B and PIWIL2 levels in iPS cells supported a causal inverse relationship between levels of these proteins and L1 retrotransposition. Finally, we found increased copy numbers of species-specific L1 elements in the genome of chimpanzees compared to humans, supporting the idea that increased L1 mobility in NHPs is not limited to iPS cells in culture and may have also occurred in the germ line or embryonic cells developmentally upstream to germline specification during primate evolution. We propose that differences in L1 mobility may have differentially shaped the genomes of humans and NHPs and could have continuing adaptive significance.