Exons 7 and 8, encoding the code region of the JmjC demethylase domain, were flanked by loxP sites. A FRT-flanked neomycin resistance gene was inserted downstream of exon 8 before the second loxP site. Cre-mediated recombination deleted exons 7 and 8 and the selection cassette in the germline. Western blot and immunostaining on brains confirmed absence of protein.