Neuron-specific PGP9.5 expression in rat hair follicle development and cycle

Protein gene product PGP9.5 is a neuron-specific ubiquitin C-terminal hydrolase. We found that it also has immunoreactivity in the hair follicle of the Wistar rat dorsal skin and its expression patterns change with the development and cycle. During the morphogenesis, the PGP9.5 was expressed in the hair germ and hair peg elongated from the epidermis, and became restricted in the outer root sheath as the development progressed. In catagen, however, the PGP9.5 was detected in the tailing epithelial strand of the regressing proximal follicle epithelium, and in the keratinocytes directly contacted with the club hair, but rarely in the outer root sheath. With the beginning of the anagen of the second hair follicle, the PGP9.5 was again expressed in the second hair germ, and in the keratinocytes surrounding the remaining club hair and of distal follicle of the first hair. These findings showed that PGP9.5 is not specific to the neuron but is also involved in the hair follicle, and should provide new insight into the development and regression of the hair follicle.