Coat Color of C57BL/6J-Bax<tm1Sjk> Mice (Stock No. 002994)

JAX® Bulletin #2
July 14, 1999

The Induced Mutant Resource at The Jackson Laboratory imported Bax targeted mutant mice from Dr. Stanley J. Korsemeyer (Knudson et al., 1995). During colony development, variation in coat color of C57BL/6J-Baxtm1Sjk mice was observed. This coat color variation is the result of coat color genes linked to the Bax gene.

The coat color loci tyrosinase (Tyr) and pink-eyed dilution (p) are linked to the Bcl2-associated X protein (Bax) gene. According to backcross data from the Mouse Genome Database, Bax is at 23.00 cM, p is at 28.00 cM, and Tyr is at 44.00 cM on chromosome 7.

The targeted disruption of the Bax gene was performed in a 129-derived RW-4 ES cell line (Aw/Aw p Tyrc-ch/p Tyrc) and has been backcrossed 8 generations to C57BL/6 (a/a +p +Tyr-c/+p +Tyr-c; nonagouti black). Statistically, C57BL/6J-Baxtm1Sjk mice should be 99.6% C57BL/6-like at all loci not linked to the Bax gene. At the present time The Jackson Laboratory’s colony of C57BL/6J-Baxtm1Sjk mice are still segregating at the Tyr locus and retain the p allele from the 129 ES cell line.

Thus, matings of Bax heterozygous (+/-) mice may produce progeny of varying coat color including black, white, chinchilla, light chinchilla, or grey, with all but the black mice having pink eyes. Because the potential for crossover between the p and Bax loci is small (roughly 5%), progeny that are grey in color and have pink eyes most likely are homozygous for the targeted Bax gene (-/-). However, we strongly recommend that you confirm the genotype of the mice prior to using them for research purposes.

The Jackson Laboratory is continuing to backcross the Bax targeted mutation to C57BL/6J to try to eliminate the recessive 129 alleles of Tyr and p. However, in an effort to make these mice available to the research community as soon as possible we will begin distribution from the current colony.

To summarize, the C57BL/6J-Baxtm1Sjk mice (Stock No. 002994) have been backcrossed 8 generations to the C57BL/6J inbred strain. However, because of coat color genes linked to the Bax mutation breeder pairs supplied by The Jackson Laboratory may produce progeny of varying coat color. The best control for BAX homozygous deficient mice is wildtype (+/+) mice from the colony. C57BL/6J mice (Stock No. 000664) may be used as controls if necessary.

For Information

Please contact Jackson Laboratory Technical Support by phone at 800 422-MICE or 207 288-6423 if you need further clarification or information about the C57BL/6J-Baxtm1Sjk mice.

Reference

Knudson CM, Tung KSK, Tourtellotte WG, Brown, GAJ, Korsmeyer SJ. 1995. Bax-deficient mice with lymphoid hyperplasia and male germ cell death. Science 270:96-99.