Mutations in genes encoding ribosomal proteins cause the Minute phenotype in Drosophila and mice, and Diamond-Blackfan syndrome in humans. Here we report two mouse dark skin (Dsk) loci caused by mutations in Rps19 (ribosomal protein S19) and Rps20 (ribosomal protein S20). We identify a common pathophysiologic program in which p53 stabilization stimulates Kit ligand expression, and, consequently, epidermal melanocytosis via a paracrine mechanism. Accumulation of p53 also causes reduced body size and erythrocyte count. These results provide a mechanistic explanation for the diverse collection of phenotypes that accompany reduced dosage of genes encoding ribosomal proteins, and have implications for understanding normal human variation and human disease.

These studies demonstrate that, in vitro and in vivo, estradiol enhances endothelial cell activities important in neovascularization and suggest a promoting influence of estrogens on angiogenesis.

Chemical mutagenesis in the mouse is a powerful approach for phenotype-driven genetics, but questions remain about the efficiency with which new mutations ascertained by their phenotype can be localized and identified, and that knowledge applied to a specific biological problem. During a global screen for dominant phenotypes in about 30,000 animals, a novel class of pigmentation mutants were identified by dark skin (Dsk). We determined the genetic map location, homozygous phenotype, and histology of 10 new Dsk and 2 new dark coat (Dcc) mutations, and identified mutations in Agouti (Met1Leu, Dcc4), Sox18 (Leu220ter, Dcc1), Keratin 2e (Thr500Pro, Dsk2), and Egfr (Leu863Gln, Dsk5). Cutaneous effects of most Dsk mutations are limited to melanocytes, except for the Keratin 2e and Egfr mutations, in which hyperkeratosis and epidermal thickening precede epidermal melanocytosis by 3-6 wk. The Dsk2 mutation is likely to impair intermediate filament assembly, leading to cytolysis of suprabasal keratinocytes and secondary hyperkeratosis and melanocytosis. The Dsk5 mutation causes increased tyrosine kinase activity and a decrease in steady-state receptor levels in vivo. The Dsk mutations represent genes or map locations not implicated previously in pigmentation, and delineate a developmental pathway in which mutations can be classified on the basis of body region, microscopic site, and timing of pigment accumulation.

Laminin-5, a major adhesive ligand for epithelial cells, undergoes processing of its ␥2 and ␣3 chains. This study investigated the mechanism of laminin-5 processing by keratinocytes. BI-1 (BMP-1 isoenzyme inhibitor-1), a selective inhibitor of a small group of astacin-like metalloproteinases, which includes bone morphogenetic protein 1 (BMP-1), mammalian Tolloid (mTLD), mammalian Tolloid-like 1 (mTLL-1), and mammalian Tolloid-like 2 (mTLL-2), inhibited the processing of laminin-5 ␥2 and ␣3 chains in keratinocyte cultures in a dose-dependent manner. In a proteinase survey, all BMP-1 isoenzymes processed human laminin-5 ␥2 and ␣3 chains to 105-and 165-kDa fragments, respectively. In contrast, MT1-MMP and MMP-2 did not cleave the ␥2 chain of human laminin-5 but processed the rat laminin ␥2 chain to an 80-kDa fragment. An immunoblot and quantitative PCR survey of the BMP-1 isoenzymes revealed expression of mTLD in primary keratinocyte cultures but little or no expression of BMP-1, mTLL-1, or mTLL-2. mTLD was shown to cleave the ␥2 chain at the same site as the previously identified BMP-1 cleavage site. In addition, mTLD/BMP-1 null mice were shown to have deficient laminin-5 processing. Together, these data identify laminin-5 as a substrate for mTLD, suggesting a role for laminin-5 processing by mTLD in the skin.Proteolysis of the extracellular matrix is emerging as a key mechanism in processes such as wound healing and tumor metastasis (1, 2). Although most studies have investigated the role of serine proteases and matrix metalloproteases, members of the astacin and ADAM (a disintegrin and metalloprotease) families have also been implicated in this process (1, 2). Laminin-5, the major component of epithelial basement membranes, is a heterotrimeric protein consisting of ␣3, ␤3, and ␥2 subunits (3, 4). Laminin-5 undergoes extracellular proteolysis of the ␣3 chain from a 200-to a 165-kDa form and of the ␥2 chain from a 155-to a 105-kDa form (5). Through its interaction with ␣ 3 ␤ 1 (6, 7), ␣ 6 ␤ 4 (8), and ␣ 2 ␤ 1 integrins (9), laminin-5 supports epithelial cell adhesion (3, 10), and migration (11, 12).Several proteases have been implicated in laminin-5 processing. Exogenous addition of matrix metalloprotease 2 (MMP-2) 1 cleaved the ␥2 subunit of rat laminin-5 (12). A subsequent study suggested that membrane type 1 matrix metalloprotease (MT1-MMP) may play a role in cleaving laminin-5 (13). Cleavage of laminin-5 by plasmin converted the ␣3 chain into the 165-kDa form observed in human breast and rat epithelial cells and capable of nucleating hemidesmosomes (14). Bone morphogenetic protein 1 (BMP-1) has also been implicated in laminin-5 proteolysis. N-terminal sequencing of the 105-kDa ␥2 chain obtained from human keratinocytes revealed a cleavage site that matched the minimal consensus sequence of this metalloprotease (15). In vitro studies demonstrated that BMP-1 cleaved the recombinant ␥2 short arm at the predicted site and that the enzyme cleaved both the ␣3 and ␥2 chains of whole laminin-5 to generate characterist...

Color markings among felid species display both a remarkable diversity and a common underlying periodicity. A similar range of patterns in domestic cats suggests a conserved mechanism whose appearance can be altered by selection. We identified the gene responsible for tabby pattern variation in domestic cats as Transmembrane aminopeptidase Q (Taqpep), which encodes a membrane-bound metalloprotease. Analyzing 31 other felid species, we identified Taqpep as the cause of the rare king cheetah phenotype, in which spots coalesce into blotches and stripes. Histologic, genomic expression, and transgenic mouse studies indicate that paracrine expression of Endothelin3 (Edn3) coordinates localized color differences. We propose a two-stage model in which Taqpep helps to establish a periodic pre-pattern during skin development that is later implemented by differential expression of Edn3.