Nucleosomes inhibit target cleavage by CRISPR-Cas9 in vivo.

Genome editing with CRISPR-Cas nucleases has been applied successfully to a wide range of cells and organisms. There is, however, considerable variation in the efficiency of cleavage and outcomes at different genomic targets, even within the same cell type. Some of this variability is likely due to the inherent quality of the interaction between the guide RNA and the target sequence, but some may also reflect the relative accessibility of the target.

Comparing zinc finger nucleases and transcription activator-like effector nucleases for gene targeting in Drosophila.

Zinc-finger nucleases have proven to be successful as reagents for targeted genome manipulation in Drosophila melanogaster and many other organisms. Their utility has been limited, however, by the significant failure rate of new designs, reflecting the complexity of DNA recognition by zinc fingers. Transcription activator-like effector (TALE) DNA-binding domains depend on a simple, one-module-to-one-base-pair recognition code, and they have been very productively incorporated into nucleases (TALENs) for genome engineering.

Donor DNA Utilization During Gene Targeting with Zinc-Finger Nucleases.

Gene targeting is the term commonly applied to experimental gene replacement by homologous recombination (HR). This process is substantially stimulated by a double-strand break (DSB) in the genomic target. Zinc-finger nucleases (ZFNs) are targetable cleavage reagents that provide an effective means of introducing such a break in conjunction with delivery of a homologous donor DNA.

High-efficiency gene targeting in Drosophila with zinc finger nucleases.

We describe a method for making targeted double-strand breaks in Drosophila melanogaster using zinc finger nucleases (ZFNs). After design and construction of the appropriate coding sequences, synthetic mRNAs for the ZFNs are injected directly into fly embryos. Frequencies of target cleavage and mutagenesis in the range of 1-10% have been achieved at several different loci.

Genetic analysis of zinc-finger nuclease-induced gene targeting in Drosophila.

Using zinc-finger nucleases (ZFNs) to cleave the chromosomal target, we have achieved high frequencies of gene targeting in the Drosophila germline. Both local mutagenesis through nonhomologous end joining (NHEJ) and gene replacement via homologous recombination (HR) are stimulated by target cleavage. In this study we investigated the mechanisms that underlie these processes, using materials for the rosy (ry) locus.

Efficient gene targeting in Drosophila by direct embryo injection with zinc-finger nucleases.

We report very high gene targeting frequencies in Drosophila by direct embryo injection of mRNAs encoding specific zinc-finger nucleases (ZFNs). Both local mutagenesis via nonhomologous end joining (NHEJ) and targeted gene replacement via homologous recombination (HR) have been achieved in up to 10% of all targets at a given locus. In embryos that are wild type for DNA repair, the products are dominated by NHEJ mutations.

Gene targeting in Drosophila and Caenorhabditis elegans with zinc-finger nucleases.

Zinc-finger nucleases (ZFNs) are promising new tools for enhancing the efficiency of gene targeting in many organisms. Because of the flexibility of zinc finger DNA recognition, ZFNs can be designed to bind many different genomic sequences. The double-strand breaks they create are repaired by cellular processes that generate new mutations at the cleavage site.

Efficient gene targeting in Drosophila with zinc-finger nucleases.

This report describes high-frequency germline gene targeting at two genomic loci in Drosophila melanogaster, y and ry. In the best case, nearly all induced parents produced mutant progeny; 25% of their offspring were new mutants and most of these were targeted gene replacements resulting from homologous recombination (HR) with a marked donor DNA. The procedure that generates these high frequencies relies on cleavage of the target by designed zinc-finger nucleases (ZFNs) and production of a linear donor in situ.