Palmoplantar keratoderma in Slurp2-deficient mice

SLURP1, a member of the Ly6 protein family, is secreted by suprabasal keratinocytes. Mutations in SLURP1 cause a palmoplantar keratoderma (PPK) known as mal de Meleda. Another secreted Ly6 protein, SLURP2, is encoded by a gene located ~20 kb downstream from SLURP1. SLURP2 is produced by suprabasal keratinocytes. To investigate the importance of SLURP2, we first examined Slurp2 knockout mice in which exon 2–3 sequences had been replaced with lacZ and neo cassettes. Slurp2(−/−) mice exhibited hyperkeratosis on the volar surface of the paws (i.e., PPK), increased keratinocyte proliferation, and an accumulation of lipid droplets in the stratum corneum. They also exhibited reduced body weight and hind limb clasping. These phenotypes are very similar to those of Slurp1(−/−) mice. To solidify a link between Slurp2 deficiency and PPK and to be confident that the disease phenotypes in Slurp2(−/−) mice were not secondary to the effects of the lacZ and neo cassettes on Slurp1 expression, we created a new line of Slurp2 knockout mice (Slurp2X(−/−)) in which Slurp2 was inactivated with a simple nonsense mutation. Slurp2X(−/−) mice exhibited the same disease phenotypes. Thus, Slurp2 deficiency and Slurp1 deficiencies cause the same disease phenotypes.