By homologous recombination targeting in ES cells, the exon (ENSMUSE00001275521) including the start codon was flanked by loxP sequences and was followed by a Pgk-neo cassette flanked by Frt sequences. The Pgk-neo cassette was removed by crossing with Rosa-Flp mice. Mice were crossed to mice expressing cre in germline to delete the exon containing the start codon. Western blot analysis confirmed the absence of protein expression in newborn ovaries from homozygous mutant females. This is a null allele.