Several Southern blot and PCR strategies were exploited in order to determine the genotype of the Capn2 locus. Southern blotting was carried out using the digoxigenin (DIG) non-radioactive system (Roche). In most cases, membranes were blotted with BamHI-digested genomic DNA and hybridized with a DIG-labeled 823 bp exon 4-containing BamHI-HindIII fragment located immediately upstream of the short arm of homology (Figure 1). A 681 bp PstI-XbaI fragment from the PGK-Neo cassette was also used to probe Southern blots in order to verify a single integration event in targeted clones.