Exon 2 of the beta form, which is exon 8 of the alpha form, was flanked by loxP sites and an FRT-flanked neomycin cassette was inserted. This codes for part of the âspacerâ region, a motif shared by other members of this family. Deletion leads to a frameshift variant with predicted loss of any remaining protein. Flp-mediated recombination removed the neomycin cassette. Exon2/8 was removed via cre-mediated recombination.