Derivation of haploid embryonic stem cells from mouse embryos

The diploid state that predominates in the genomes of complex organisms limits the variety of genetic approaches that can be used in biomedical model species such as mice. It has been previously suggested that because of the specifics of mammalian genetics, such as genomic imprinting and X inactivation, it is not possible to derive haploid stem cells from mice. But a study by Martin Leeb and Anton Wutz reports the successful production of mouse haploid embryonic stem cells. The cell lines can be established in culture and will open new possibilities for genetic screening in mammals. Most animals are diploid, but haploid-only and male-haploid (such as honeybee and ant) species have been described1. The diploid genomes of complex organisms limit genetic approaches in biomedical model species such as mice. To overcome this problem, experimental induction of haploidy has been used in fish2,3. Haploid development in zebrafish has been applied for genetic screening2. Recently, haploid pluripotent cell lines from medaka fish (Oryzias latipes) have also been established3. In contrast, haploidy seems less compatible with development in mammals4,5. Although haploid cells have been observed in egg cylinder stage parthenogenetic mouse embryos6, most cells in surviving embryos become diploid. Here we describe haploid mouse embryonic stem cells and show their application in forward genetic screening.