The Ptpmt1flox (floxed exons 1-2) allele was created in the laboratory of Dr. Jack E. Dixon (University of California, San Diego). First, a targeting vector was designed to insert a loxP site upstream of exon 1, and an frt-flanked neo cassette followed by a second loxP site downstream of exon 2 of the protein tyrosine phosphatase mitochondrial 1 locus (Ptpmt1) on chromosome 2. The targeting vector was electroporated into (129X1/SvJ x 129S1/Sv)F1-Kitl+-derived R1 embryonic stem (ES) cells. Chimeric animals were bred to C57BL/6J mice for germline transmission. The Ptpmt1targeted mutant mice were then bred with FLPe-deleter mice (Tg(ACTFLPe)9205Dym on an undisclosed genetic background) for germline removal of the neo cassette. The resulting Ptpmt1flox offspring were selected. The donating investigator reported that the Ptpmt1flox colony was backcrossed to C57BL/6J wildtype mice for several generations (and the FLP-expressing transgene was removed) (see SNP note below). In 2017, Ptpmt1targeted males with black coat color were sent to The Jackson Laboratory Repository. Upon arrival, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).
Of note, it is not known if the Y chromosome has been fixed to the C57BL/6 background during backcrossing.
In 2017, a 48 single nucleotide polymorphism (SNP) panel analysis, with markers covering all 19 chromosomes and the X chromosome, as well as several markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the males sent to The Jackson Laboratory Repository. This revealed several markers were not fixed for C57BL/6 allele-type (i.e., still segregating for 129S and other allele-type markers). Collectively, these data suggest that the mice sent to The Jackson Laboratory Repository were incompletely backcrossed onto C57BL/6, and the genetic background of the mice was more than 50% C57BL/6 with contributions from other mouse genetic backgrounds.
