CRISPR/Cas9 system inserted a cassette encoding a viral 2A oligopeptide (T2A) self-cleaving peptide, that mediates ribosomal skipping, fused to an C-terminal Cre recombinase fragment (CCre), directly downstream of the chemokine (C-X3-C motif) receptor 1 (Cx3cr1) gene. (J:302588)