The field of genomic engineering is changing quickly during the last years. Beginning with custom zinc finger nucleases in 2009, a number of techniques have been established to facilitate the introduction of deletions and mutations into mammalian genes via specific nucleases.
The most effective systems are CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) and TALENs (Transcription Activator-Like Effector Nucleases). These techniques allow for direct manipulation of genes within the oocyte by injection into the pronucleus of mice, rats or other animal models. Transfection of the nucleases into cell lines allows the introduction of genetic changes in a very efficient way.