Table 1.

Overview of genome editing and gene silencing technologies.

Name	Components	Mechanism of action	Specificity/off-target effects	Possibility to rapidly generate large-scale libraries
Genome editing
Zinc finger nucleases (ZFNs)	Fok1 restriction nuclease fused to multiple zinc finger peptides; each targeting 3 bp of genomic sequence	Induces double-strand breaks in target DNA	Can have off-target effects	No – requires customization of protein component for each gene
Transcription activator-like effector nucleases (TALENs)	Non-specific DNA-cleaving nuclease fused to a DNA-binding domain specific for a genomic locus	Induces double-strand breaks in target DNA	Highly specific	Feasible, but technically challenging (Reyon etal., 2012)
Homing meganucleases	Endonuclease with a large recognition site for DNA (12–40 base pairs)	Induces double-strand breaks in target DNA	Highly specific	No – limited target sequence specificity available
CRISPR/Cas	20 nt crRNA fused to tracrRNA and Cas9 endonuclease	Induces double-strand breaks in target DNA (wt Cas9) or single-strand DNA nicks (Cas9 nickase)	Some off-target effects that can be minimized by selection of unique crRNA sequences	Yes – requires simple adapter cloning of 20 nt Oligos targeting each gene into a plasmid
Gene silencing
Post-transcriptional gene silencing (e.g., RNA interference)	Double-stranded RNA	DICER-mediated mRNA degradation; (post-transcriptional)	Can have significant off-target effects	Yes (Moffat etal., 2006)
Morpholino oligonucleotides	Synthetic oligonucleotide analogs	Sterical blocking of translation initiation complex; (post-transcriptional)	Can have significant off-target effects	Feasible, but technically challenging
CRISPRi	sgRNA and catalytically inactive Cas9	Transcriptional repression of RNA synthesis	To be determined	Yes