Elling, U. et al. Nature 550, 114–118 (2017).

When trying to understand the function of a gene, ideally a clone carrying a mutation is compared with an otherwise identical clone that carries the wild-type gene. Current mutagenesis approaches, while able to efficiently introduce mutations, do not easily produce pools of clones that vary only in a single mutation. An international team of researchers led by Ulrich Elling and Josef Penninger from the Institute of Molecular Biotechnology of the Austrian Academy of Sciences systematically targeted 16,970 mouse genes in haploid embryonic stem cells (ESCs) with barcoded vectors to achieve insertional mutagenesis. Flanking recombination sites allowed for two reversals of the vector, which made it possible to restore wild-type gene expression followed by another inactivation of the gene. The team used the resource to, for example, profile genes needed for resistance to a common cold virus. Clones are available at https://www.haplobank.at/.