Modulating and targeting meiotic double-strand breaks in Saccharomyces cerevisiae

Programming sites of meiotic crossovers using Spo11 fusion proteins

Meiotic recombination shapes the genetic diversity transmitted upon sexual reproduction. However, its non-random distribution along the chromosomes constrains the landscape of potential genetic combinations. For a variety of purposes, it is desirable to expand the natural repertoire by changing the distribution of crossovers in a wide range of eukaryotes. Toward this end, we report the local stimulation of meiotic recombination at a number of chromosomal sites by tethering the natural Spo11 protein to various DNA-binding modules: full-length DNA binding proteins, zinc fingers (ZFs), transcription activator-like effector (TALE) modules, and the CRISPR-Cas9 system. In the yeast Saccharomyces cerevisiae, each strategy is able to stimulate crossover frequencies in naturally recombination-cold regions. The binding and cleavage efficiency of the targeting Spo11 fusions (TSF) are variable, being dependent on the chromosomal regions and potential competition with endogenous factors. TSF-mediated genome interrogation distinguishes naturally recombination-cold regions that are flexible and can be warmed-up (gene promoters and coding sequences), from those that remain refractory (gene terminators and centromeres). These results describe new generic experimental strategies to increase the genetic diversity of gametes, which should prove useful in plant breeding and other applications.

The democratization of gene editing: Insights from site-specific cleavage and double-strand break repair

DNA double-strand breaks (DSBs) are dangerous lesions that if not properly repaired can lead to genomic change or cell death. Organisms have developed several pathways and have many factors devoted to repairing DSBs, which broadly occurs by homologous recombination, which relies on an identical or homologous sequence to template repair, or nonhomologous end-joining. Much of our understanding of these repair mechanisms has come from the study of induced DNA cleavage by site-specific endonucleases. In addition to their biological role, these cellular pathways can be co-opted for gene editing to study gene function or for gene therapy or other applications. While the first gene editing experiments were done more than 20 years ago, the recent discovery of RNA-guided endonucleases has simplified approaches developed over the years to make gene editing an approach that is available to the entire biomedical research community. Here, we review DSB repair mechanisms and site-specific cleavage systems that have provided insight into these mechanisms and led to the current gene editing revolution.