Physical Localization of the Mouse aryl hydrocarbon receptor nuclear translocator-2 (Arnt2) Gene within the c 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 super(112K) deletion identifies a putative thymus functional region not removed by the overlapping c super(3H) deletion. Cloning the c super(3H) proximal breakpoint provided a starting point for construction of an 840-kb BAC contig spanning the c super(112K) and c super(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 super(112K) deletion and spans 130-170 kb of the interval. Although Arnt2 is a candidate for the thymus defects in c super(112K) homozygotes, the possibility that other as yet unidentified genes in the c super(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 super(112K) homozygotes markedly contrasts the embryonic lethality observed in Arnt-deficient embryos and suggests distinct roles for these related transcription factors during embryogenesis.