Prolactin signaling influences the timing mechanism of the hair follicle: Analysis of hair growth cycles in prolactin receptor knockout mice

Pituitary PRL regulates seasonal hair follicle growth cycles in many mammals. Here we present the first evidence implicating PRL in the nonseasonal, wave-like pelage replacement of laboratory mice. In this study we show that messenger RNA transcripts encoding the one long and two short forms of PRL receptor are present in the skin of adult and neonate mice. The receptor protein was immunolocalized to the hair follicle as well as the epidermis and sebaceous glands. Furthermore, PRL messenger RNA was detected within skin extracts, suggesting a possible autocrine/paracrine role. Analysis of the hair growth phenotype of PRL gene-disrupted mice (PRLR−/−) revealed a change in the timing of hair cycling events. Although no hair follicle development differences were noted in PRLR−/− neonates, observations of the second generation of hair growth revealed PRLR−/− mice molted earlier than wild types (PRLR+/+). The advance was greater in females (29 days) than in males (4 days), resulting in the elimination of the se...