Colourless Side of the Nude Mutation: Foxn1 and Hair Pigmentation

The study explored the role of the Foxn1 gene in hair pigmentation, particularly in nude mice, which are characterized by malformed hair shafts due to a lack of certain hair keratins. It was found that Foxn1 is crucial for directing keratinocytes to receive pigment from melanocytes, and its expression in basal keratinocytes led to ectopic skin pigmentation in transgenic mice. Despite normal melanocyte migration and pigment production, nude mice exhibited little cortical hair pigmentation due to unpigmented cortical keratinocytes. This suggested that pigment recipient cells instruct melanocytes on pigment placement. In humans, Foxn1 is expressed in normal skin to attract melanocytes, although the human nude phenotype does not show pigment abnormalities, indicating differences in molecular mechanisms between species. The study also highlighted the potential role of FGF2 as a downstream attractant of Foxn1, and the involvement of phospholipase C-δ1 in the nude phenotype, emphasizing the need to further investigate the molecular pathways involved in pigment transfer and Foxn1 function.