Gender disparity in survival of early porcine fetuses due to altered androgen receptor or associated U2 spliceosome component

A single locus on the X chromosome codes for androgen receptor (AR) although this gene is subject to alternative splicing. AR is expressed in multiple tissues in males and females and is essential for reproductive success in the male. Since male and female mice are viable following naturally occurring and engineered loss of function with male mice infertile as anticipated, functional deletion of AR in pigs was hypothesized to provide a genetic containment strategy for males with edited genomes. In addition, deletion of AR might be a method to manage boar taint, hence contributing to a perceived improvement in animal welfare. The CRISPR/Cas9 technology was used to edit either exon 2 or exon 5 of the pig AR gene. Although pregnancies were established following embryo transfer of edited embryos, they were not maintained beyond day 25. Furthermore, normal M:F sex ratios were present in edited blastocysts and 19-day fetuses, but all fetuses recovered on day 21 or later were female. The pig AR gene differs from the mouse in having a U2 spliceosome component encoded in the intronic region. Hence, the absence of fetal survival beyond day 25 may be due to interference with the U2 component rather than AR.