Li, W. et al. Cell Stem Cell doi:10.1016/j.stem.2013.11.016 (19 December 2013).

The study of gene function in diploid organisms such as the rat is impeded by the fact that each gene exists as two copies. Li et al. report the derivation of androgenetic haploid embryonic stem cells (ESCs) from the Dark Agouti rat. They remove the maternal pronucleus after fertilization, mature the embryos in vivo to the blastocyst stage and derive ESCs from harvested embryos under established conditions. Periodic FACS permits stable maintenance of haploid cells in culture over many passages. Haploid rat ESCs display many markers of pluripotency, including contribution to all germ layers and to the germ line in chimeras, although differentiation results in diploidization as has been seen for mouse. The cells remain haploid upon mutagenesis by random or targeted methods and will contribute to the study of gene function in this model organism.