No abstract

Several dominant mutations of the mouse agouti coat colour gene have pleiotropic effects that include obesity and a yellow coat. The Ay allele is caused by a large deletion that affects the expression of several contiguous genes. We show that three other obesity-associated agouti mutations, Aiy, Asy and Avy, are due to different molecular alterations that result in ubiquitous expression of a chimaeric RNA that encodes a normal agouti protein. The Aiy and Avy alleles are caused by insertion of an intracisternal A particle element 1 kb or 100 kb, respectively, upstream of agouti coding sequences. These results provide a model for other genes that show allele-specific imprinting, and demonstrate that molecular mechanisms typically responsible for activation of proto-oncogenes can also lead to other disease phenotypes.

The mouse agouti gene controls the deposition of yellow and black pigment in developing hairs. Several dominant alleles, including lethal yellow (AY), result in the exclusive production of yellow pigment and have pleiotropic effects that include obesity and increased tumor susceptibility. In an interspecific backcross, we established genetic limits for the agouti gene and found that the A y and the lethal non=agouti (a'q allele were not separated from a previously identified probe at the breakpoint of the IslGsO chromosomal rearrangement.Using the IslGsO probe, we isolated the agouti gene, and find that it has the potential to code for a secreted protein expressed in hair follicles and the epidermis, and that the level of expression correlates with the synthesis of yellow pigment. In the A y mutation, there is a chromosomal rearrangement that results in the production of a chimeric RNA expressed in nearly every tissue of the body. The 5' portion of this chimeric RNA contains highly expressed novel 5' sequences, but the 3' portion retains the protein-coding potential of the nonmutant allele. We speculate that dominant pleiotropic effects of A y are caused by ectopic activation of a signaling pathway similar to that used during normal hair growth.

PARP1-mediated poly(ADP-ribosyl)ation of DDB2 prolongs its occupation on UV-damaged chromatin and promotes the recruitment of the chromatin remodeler ALC1.

Primary DNA damage sensing in mammalian global genome nucleotide excision repair (GG-NER) is performed by the xeroderma pigmentosum group C (XPC)/HR23B protein complex. HR23B and HR23A are human homologs of the yeast ubiquitin-domain repair factor RAD23, the function of which is unknown. Knockout mice revealed that mHR23A and mHR23B have a fully redundant role in NER, and a partially redundant function in embryonic development. Inactivation of both genes causes embryonic lethality, but appeared still compatible with cellular viability. Analysis of mHR23A/B double-mutant cells showed that HR23 proteins function in NER by governing XPC stability via partial protection against proteasomal degradation. Interestingly, NER-type DNA damage further stabilizes XPC and thereby enhances repair. These findings resolve the primary function of RAD23 in repair and reveal a novel DNA-damage-dependent regulation mechanism of DNA repair in eukaryotes, which may be part of a more global damage-response circuitry.