Pre-determination of sex in pigs by application of CRISPR/Cas system for genome editing
In livestock industries, one sex is usually preferred because of the impact on the production (e.g. milk from cows, eggs from laying hens). Furthermore, in pig production, the male-specific boar taint is a big hurdle for consumer acceptance. Consequently, a shift in the ratio towards the desired sex would be a great benefit. The most widely applied method for pre-determination of the sex is fluorescence-activated sperm sorting, which relies on the different DNA content of the X- and Y-chromosomal sperm. However, the successful practical adaption of this method depends on its ease of use. At present, sperm sexing via fluorescence-activated cell sorting has only reached commercial application in cattle. Nevertheless, sperm sexing technology still needs to be improved with respect to efficiency and reliability, to obtain high numbers of sexed sperm and less invasive sperm treatment to avoid damage. New genome editing technologies such as Zinc finger nucleases (ZFN), Transcription-activator like endonucleases (TALENs) and the CRISPR/Cas system have emerged and offer great potential to affect determination of the sex at the genome level. The sex-determining region on the Y chromosome (SRY) serves as a main genetic switch of male gender development. It was previously shown that a knockout of the SRY gene in mice and rabbits displayed suppressed testis development in the fetal gonadal ridges resulting in a female phenotype. These new technologies hold great opportunities to pre-determine sex in pigs. However, further investigations are needed to exploit their full potential for practical application.