Accelerated proliferation and abnormal differentiation of epidermal keratinocytes in Endo-β-galactosidase C transgenic mice

Transgenic (TG) mice that have systemically expressed Endo-beta-galactosidase C (EndoGalC) have rough and flaky skin. This skin phenotype is detectable around 5 days postnatal and becomes obscure by 2 weeks after birth. Their epidermis is thickened but the dermis and hair follicles are normal in structure. EndoGalC, which removes the terminal Gal alpha 1-3Gal disaccharide (alpha Gal epitope), was expressed in the epidermis of TG mice. GS-IB4 lectin staining showed that the alpha Gal epitope did not exist in the epidermis in TG but existed in wild-type (WT) mice. In TG mice,N-acetylglucosamines were exposed by EndoGalC, which is detected using GS-II lectin. To understand the cause of the epidermal thickening and skin phenotype, we examined the proliferation and differentiation of kerationocytes. BrdU-pulse-labeling revealed that proliferating keratinocytes increased approximately three-fold in TG epidermis compared to WT one. In TG epidermis, the expression domain of cytokeratin 14 increased from 1-2 layers to 4-5 layers and co-expressed with cytokeratin 6 and 10 in the upper layers. The layers expressing involucrin and loricrin also increased but those expressing filaggrin and transglutaminase looked normal. The localization of E-cadherin was similar in both TG and WT mice. Although TG mice showed delayed development of the barrier function around 8 days postnatal, they acquired the function by 12 days after birth. These results suggest that the absence of the alpha Gal epitope or the exposed N-acetylglucosamine terminal could play a critical role in the proliferation of basal keratinocytes and differentiation of them into the spinous cells in newborn mice.