What is the relationship between keratinocytes and melanocytes?

The interaction of keratinocytes and melanocytes is vital for the homeostasis of the epidermis. Melanocytes synthesize melanin and then transfer them to the keratinocytes for processing. Within keratinocytes, melanin accumulates in the supranuclear region, protecting the genetic material from UVR-induced damage. After melanin has been processed by melanocytes, they are moved inside the keratocytes and pigments are retained to provide the skin and hair with color. Melanocytes in the skin exist at the basal layer of the epidermis, where they extend dendrites upwards into the epidermis until they come into contact with about 30-40 keratinocytes and attach to the basement membrane. This formation is known as the epidermal melanin unit. Melanocyte division is likely initiated by keratinocyte-derived growth factors. Additionally, melanocyte division can be initiated by fibroblast growth factors such as hepatocyte growth factor. In the hair bulb, melanocytes exist at the base pair of the growing shaft hair and extend dendrites into keratinocytes as they enter the shaft. This formation is known as the follicular melanin unit.