Mast cell hyperplasia in the skin of Dsg4-deficient hypotrichosis mice, which are long-living mutants of lupus-prone mice

Desmosomal cadherins are essential cell adhesion molecules expressed in the epidermis. We identified a mutation of a cadherin superfamily member, namely, desmoglein 4 (Dsg4), in early onset of death (EOD) ^hage mice with hypotrichosis. The mutation was induced by the insertion of an early transposon II-β into intron 8 of Dsg4. Mast cell hyperplasia was observed in the skin of EOD ^hage mice. The abnormally expanded population of lpr T cells, i.e., CD4^-CD8^-B220⁺Thy1.2⁺ αβT cells, in the splenocytes of EOD mice was reduced in EOD ^hage mice. Therefore, it was suspected that the long-living mutant EOD ^hage mice were selected from lupus-prone EOD mice because of their immunological immaturity. These findings clearly indicate that Dsg4 is an important molecule for the formation of hair follicles and hypothesize that unorganized hyperplastic hair follicles in anagen due to the Dsg4 mutation provide niches for mast cell precursors in the skin.