Generation and maintenance of Dmbx1 gene-targeted mutant alleles

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.