This &ldquo;safe harbor landing pad&rdquo; allele on the FVB/NJ background 
provides a tool for precise, site-specific insertion of single-copy 
sequence into the Gt(ROSA)26Sor intron 1 in a manner that is in
 the desired orientation and free from vector sequence. In practice, a 
plasmid containing a single cognate 38 bp attB-GT site and the 
donor sequence is first converted into a vector-less DNA minicircle 
donor. The DNA minicircle is delivered along with the Bxb1 integrase 
(mRNA or protein) into the pronucleus of fertilized oocytes containing 
the 48 bp attP-GT landing pad attachment site. The result is a unidirectional, single-copy integration of the sequence into the Gt(ROSA)26Sor locus. The inserted sequence will be flanked by the recombined attachments sites, now called Bxb1 attL and Bxb1 attR,
 but will be: (1) free from residual vector sequence from the plasmid 
backbone, (2) present as a single-copy (no concatemers), and (3) 
inserted precisely into a known and verifiable locus (Gt(ROSA)26Sor). [<a href="https://pubmed.ncbi.nlm.nih.gov/35361849/">Low et al., 2022</a>]
 The donating investigator indicates that 5% of integrations result in 
aberrant integration events. In addition, RMKI strategy is successful 
with inserts up to approximately 15 kb. Both heterozygous and homozygous mice are viable and fertile with normal
 breeding, and no reported gross phenotypic or behavioral abnormalities.

The use of this mouse model is subject to the terms and conditions of the Limited Use Label License from Caribou Biosciences, Inc.

The use of this mouse strain or other product (the "Licensed Product") is subject to the terms and conditions of the Limited License from The Broad Institute.

Use of MICE by companies or for-profit entities requires a no-fee JAX Leap License prior to shipping.

RosaBxb-GT mice are a resource for the rapid creation of vector-free targeted alleles in the Gt(ROSA)26Sor locus on the FVB/NJ background. The single Bxb1 integrase attP-site "safe harbor landing pad" in the first intron of Gt(ROSA)26Sor enables efficient and precise integration of a donor DNA sequence directly in zygotes by recombinase-mediated knock-in (RMKI) using vector-free minicircle donor DNA carrying the transgene of interest and the cognate attB-GT attachment site.

This strain is hosted by NIH's MMRRC, which partners with JAX for the distribution of this and other strains. For additional information and to purchase, please visit the MMRRC site.