Gene expression of mouse S100A3, a cysteine-rich calcium-binding protein, in developing hair follicle.

We have previously identified a cysteine-rich calcium binding protein S100A3 present in the cuticle of human hair fiber. In this study, we cloned a cDNA for mouse S100A3, identified its gene location, and elucidated the expression profile throughout hair follicle development. The mouse S100A3 gene was clustered with other S100 family members on chromosome 3, and specifically expressed in dorsal skin containing hair follicles. The level of S100A3 mRNA was elevated during the anagen phase of the hair growth cycle, and sharply declined from the regression phase on. In situ hybridization revealed that the S100A3 gene was prominently expressed in cuticular cells of the hair follicle, and mRNA levels were highest in the keratogenous zone over the entire cuticular layer. Expression was also observed to a lesser extent in differentiated cortical cells; however, expression was not observed in any other component of the hair follicle or dorsal tissues. Immunohistochemical analysis showed that the S100A3 protein accumulated in cuticular and cortical cells undergoing terminal differentiation. These results indicate that the S100A3 gene is exclusively expressed, and the translation product retained, in follicular cells differentiating into major components of the hair shaft. It seems likely that S100A3 plays an important role in calcium-dependent processes leading to hair shaft formation.