Physical localization of the mouse aryl hydrocarbon receptor nuclear translocator-2 (Arnt2) gene within the c(112K) deletion

The albino deletions identify at least seven functional intervals essential for pre- and postnatal development in the 6- to 10-cM region surrounding the albino coat color (c = tyrosinase) locus on mouse chromosome 7. The c(112K) deletion identifies a putative thymus functional region not removed by the overlapping c(3H) deletion. Cloning the c(3H) proximal breakpoint provided a starting point for construction of an 840-kb BAC contig spanning the c(112K) and c(3H) (D7Ssb3Hp) proximal breakpoints. These breakpoints are separated by 320-350 kb. The aryl hydrocarbon receptor nuclear translocator-2 (Arnt2) is completely removed by the c(112K) deletion and spans 130-170 kb of the interval. Although Arnt2 is a candidate for the thymus defects in c(112K) homozygotes, the possibility that other as yet unidentified genes in the c(112K) deletion are responsible for the abnormalities has not been ruled out. Arnt2 is a member of the bHLH-PAS (Per, Ahr, Arnt, Sim) family of transcription factors and shares the highest similarity with Arnt. The survival of c(112K) homozygotes markedly contrasts the embryonic lethality observed in Arnt-deficient embryos and suggests distinct roles for these related transcription factors during embryogenesis.