Dmbx1 encodes a paired-like homeodomain protein that is expressed in neural tissues at mouse embryonic and postnatal stages. We previously generated two Dmbx1 mutant alleles, Dmbx1 - and Dmbx1 z , by homologous recombination in mouse embryonic stem (ES) cells. In this article we report the generation of three novel Dmbx1 mutant alleles, Dmbx1 τZ , Dmbx1 τG , and Dmbx1 Cre , that carry the intronic insertion of tau (τ)-lacZ, τ-eGFP, and Cre reporter genes, respectively. Dmbx1 τZ and Dmbx1 τG recapitulated the Dmbx1 expression, and the reporter gene expression was detected in the diencephalon and mesencephalon during embryogenesis. The crossing of Dmbx1 Cre mice with Rosa26 reporter mice identified the Cre-mediated DNA excision in the postnatal midbrain, cerebellum, medulla oblongata, and spinal cord. To maintain the Dmbx1 mutant alleles without genotyping, we crossed Dmbx1 mutant mice with Inv4(1) Brd mice that possess the inversion between D4Mit117 and D4Mit281 on Chromosome 4, where Dmbx1 is located. The intercrossing of the non-agouti (a/a) albino (Tyr c-Brd /Tyr c-Brd ) Dmbx1 mutant mice carrying Inv4(1) Brd tagged with K14-Agouti and Tyrosinase coat-color markers resulted in the generation of dark brown Dmbx1 wild-type [Inv4(1) Brd /Inv4(1) Brd ], light brown Dmbx1 heterozygous [Dmbx1 tm /Inv4(1) Brd ], and albino Dmbx1 homozygous (Dmbx1 tm /Dmbx1 tm ) mutant mice. To our knowledge, this is the first demonstration of the proof-of-principle of the maintenance of viable gene-targeted alleles using coat-color-tagged nonlethal balancer chromosomes.
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