Figure 1.

Mice expressing an enzymatically inactive caspase-8 transgene develop a skin disorder. (A) PCR genotyping of the caspase-8 BAC transgenes. Left, genotyping of WT mice and of mice expressing the WT caspase-8 transgene and either WT or KO endogenous caspase-8 alleles. Right, restriction analysis distinguishing the enzymatically inactive caspase-8 transgene (BAC-C362S) from WT (BAC-WT) transgene and endogenous allele. The arrow points to the HindIII fragment specifically generated in the BAC-C362S transgene. (B) Western blot analysis of caspase-8 in Casp-8^+/+/BAC-WT transgenic mouse tissues, relative to the WT (right and left lanes, respectively, for each pair), demonstrating its increased expression in all transgenic mouse tissues (top). Internal ribosome entry site (IRES)–aided expression of GFP cDNA (inserted into the BAC under control of the caspase-8 promoter) is proportional to that of endogenous caspase-8 (middle). Immunoblot analysis of β-actin confirmed equal loading of tissue extracts from the two mice (bottom). (C) General appearance of control and transgenic mice. At P5, pallor and thickening in the interscapular area and dorsally at the caudal head indicate early lesions. At P14, the mutant is markedly smaller, with scaling, loss of hair, and a small lesion on the left thigh. Lesion distribution is multifocal and random. (D) Microscopy of the skin. At P0, skin samples from WT and mutant mice are similar. At P7, the latter demonstrate epidermal hyperplasia and multifocal dermal inflammatory cellular infiltration. Hematoxylin and eosin (H&E); Bars, 100 µm. (E) Transgenic mouse specimens demonstrate multifocal cellular inflammatory infiltration in diaphragmatic parietal pleura, lung visceral pleura, and interstitium of pancreas and lung (arrows). Bars, 100 µm. The data presented in B, C, D, and E are representative of analyses of four, five, three, and three mice, respectively.