Notice for users of C57BL/6N-BAC-cre transgenic mouse series

We, the Experimental Animal Division, RIKEN BioResource Center, inform you of the correction of the information about the Living Modified Organisms (LMOs) and ask your attention in use of the C57BL/6N-BAC-cre transgenic mouse series* shipped to you previously.

* C57BL/6N-BAC-cre transgenic mouse series: Nes-cre (RBRC0370203703), Tek-cre (RBRC03747), Vil1-cre (RBRC03801), Vil1-cre/Esr1(RBRC03812), Ins1-cre (RBRC0393303934), Insl-cre/Esr1(RBRC03949), and Wap-cre (RBRC03964)

We were recently informed by a user of one of the BAC-cre transgenic mouse series that there could be loxP in the transgene. After receiving this information, we have examined the BAC-cre transgenic mouse series and detected a part of the pBAC3.6e vector containing loxP in the transgene by PCR, which was not described in the Information about LMOs.

We sincerely apologize for any inconvenience and troubles this may cause. Please correct by adding “Phage P1 loxP derived from pBACe3.6” to the “Introduced gene” of the Information about LMOs and ensure that this correction will be transferred to your associates.

We examined the genotype of these strains by PCR between the promoter and cre, and the Cre expression for some strains by crossing with ROSA26-lacZ reporter mice. However, we have not tested the presence of loxP, since we have been unaware of loxP in the transgene. Therefore, we ask your attention to the possibility of unintended recombination especially when you cross these mouse strains with other strains containing cre or loxP including conditional knockout mice.

Besides, we have not tested the copy number of the transgenes. If the strain carries multiple transgenes in tandem, there is a possibility, depending on the strains or experiments, of self-excision or recombination of the transgenes by Cre recombinase expressed from the transgene itself in cells where the promoter becomes active.

We are anxious to know whether you have obtained expected results by using these strains or not. If you have noticed any problems and concerns by these mouse strains, please let us know (

Through this unfortunate lesson, we promise you that we will make every effort to communicate with the depositor/developer and collect accurate information of genetic modifications from them. Furthermore, we have expanded our genetic quality control tests for BAC transgenic mice to detect loxPs derived from BAC vectors in the transgenes as the preventive measures.

We would like to reaffirm you of our commitment to providing high quality mouse strains and accurate information on the genetic modifications of the mutant mice.

Thank you very much for your attention and consideration.


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