br Acknowledgments We thank Mrs

Acknowledgments We thank Mrs Jessica Franzot for technical support with Western blotting. This work was supported by grants from the government of the Friuli Venezia Giulia Region (SPINAL project), the Fund for Transregional Cooperation (MINA project), and the IBRO Return Home Programme Grant (to MM). AD was supported by the project DIANET, 2007/2013 Operational Program of the European Social Fund of the autonomous Region Friuli Venezia Giulia.
Introduction Pluripotent stem (-)-p-Bromotetramisole Oxalate Supplier (PSCs) allow experimental access to cell types and differentiation stages that are difficult or impossible to investigate in humans. Similarly, PSCs from non-human primates would allow to study the molecular and cellular basis of human-specific traits, as recently shown for the differential regulation of LINE-1 transposons in human and ape PSCs (Marchetto et al., 2013). In addition to studying differences, human and non-human PSCs could be very useful to analyze conserved features of molecular and cellular phenotypes (Enard, 2012). On the level of DNA, evolutionary conservation is an established and highly useful measure e.g. to infer the functional relevance of disease associated mutations (Cooper and Shendure, 2011). In a similar manner, evolutionary conservation should be helpful to infer the functional relevance at the level of molecular and cellular phenotypes and it has been used e.g. to analyze regulatory networks of stress response in fungi (Roy et al., 2013) or to compare transcriptional patterns of human and murine immune cells (Shay et al., 2013). Primate PSCs, in particular induced pluripotent stem cells (iPSCs) and their derivatives could be a practically feasible way to exploit this kind of information for humans\' closest relatives. Although it has been shown that iPSCs can be generated from a range of primates (Marchetto et al., 2013; Wu et al., 2010; Wunderlich et al., 2012; Ben-Nun et al., 2011; Liu et al., 2008), a quantitative assessment on how molecular phenotypes like expression patterns differ among primate PSCs has not been described. As a first step in this direction, we have generated and characterized human, gorilla, bonobo and cynomolgus monkey iPSCs. We demonstrate that they have comparable differentiation potentials that are similar to human, cynomolgus and rhesus monkey embryonic stem cells (ESCs), and that their gene expression patterns evolve fast, but under considerable constraint. Our results show that primate iPSCs can provide a rich source to identify conserved and species-specific gene expression patterns for cellular phenotypes in humans\' closest relatives.
Material and methods
Results and discussion
Conclusions In summary, we show that iPSCs are a practical and promising tool to analyse molecular and cellular phenotypes among primates. Despite very similar morphology, culture characteristics and general differentiation potential, expression differences between PSCs of the analyzed primates are more than 3-fold larger than differences between individual PSC clones. But since pseudogenes differ twice as much, expression levels are also constrained in their evolution. These patterns are of similar magnitude as in various somatic tissue types. Thus, primate iPSCs are likely to be informative for identifying conserved and derived expression patterns. Maybe the most informative will be the use of such cells to analyze the evolution of gene expression and regulatory networks during cell differentiation (e.g. Roy et al., 2013; Gifford et al., 2013). Hence, we think that primate iPSCs will become an important tool for understanding primate evolution on a cellular and molecular level. The following are the supplementary data related to this article.
Acknowledgments We thank Ines Bliesener and Victor Wiebe (MPI-EVA) for their excellent technical support. This work was funded by the Max Planck Society (M.K., W.E. and S.P.) and by the German Research Foundation (Cluster of Excellence REBIRTH, EXC 62/3).