Plasmids encoding a guide RNA (ACTCCAGTCTTTCTAGAAGA) were designed to insert a cassette encoding a CMV-IE enhancer/chicken beta-actin/rabbit beta-globin hybrid promoter (CAG) followed by a floxed STOP cassette and a 3xHA (hemaglutinin) C-terminal tagged Insm1 gene into the Gt(ROSA)26Sor locus. A viral 2A oligopeptide (T2A) self cleaving peptide, that mediates ribosomal skipping, fused to a red fluorescent protein sequence (tdTomato) was inserted downstream. (J:336865)