A targeting vector was designed by the laboratory of Dr. Brian Sauer (while at Oklahoma Medical Research Foundation) to delete the MHL-1 major subunit coding region in exon 2 of the asialoglycoprotein receptor 1 (Asgr1; also known as hepatic lectin-1 [HL-1]) locus and insert a loxp-flanked PGKneo cassette (followed by a synthetic lox511 site) two nucleotides before the Asgr1 translational start site. This construct was electroporated into 129S4/SvJae-derived J1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric offspring were bred with C57BL/6J mice to generate the mutant colony. These MHL-1 null (or Asgr1 null) mice were backcrossed for at least six generations to C57BL/6J and then sent to Dr. Jamey D. Marth (at University of California San Diego). The donating investigator reported that these Asgr1 null mice were backcrossed to C57BL/6NHsd mice (see SNP note below) for at least six generations. Upon arrival at The Jackson Laboratory Repository, mice were bred to C57BL/6NJ (Stock No. 005304) for at least one generation to establish the colony. During backcrossing, the Y chromosome may not have been fixed to the C57BL/6N genetic background.
A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the rederived living colony at The Jackson Laboratory Repository. While the 27 markers throughout the genome suggested a C57BL/6 genetic background, at least 1 of 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating. These data suggest the mice sent to The Jackson Laboratory Repository were on a mixed C57BL/6J ; C57BL/6N genetic background.
