Aj. Craven et al., Prolactin signaling influences the timing mechanism of the hair follicle: Analysis of hair growth cycles in prolactin receptor knockout mice, ENDOCRINOL, 142(6), 2001, pp. 2533-2539
Pituitary PRL regulates seasonal hair follicle growth cycles in many mammal
s. Here we present the first evidence implicating PRL in the nonseasonal, w
ave-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 pr
otein 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 h
air growth phenotype of PRL gene-disrupted mice (PRLR-l-) revealed a change
in the timing of hair cycling events. Although no hair follicle developmen
t differences were noted in PRLR-l- neonates, observations of the second ge
neration of hair growth revealed PRLR-l- mice molted earlier than wild type
s (PRLR+/+). The advance was greater in females (29 days) than in males (4
days), resulting in the elimination of the sexual dimorphism associated wit
h murine hair replacement. Heterozygotes were intermediate between PRLR-l-
and PRLR+/+ mice in molt onset. Once initiated, the pattern and progression
of the molt across the body were similar in all genotypes. Although all fi
ber types were present and appeared structurally normal, PRLR-l- mice had s
lightly longer and coarser hair than wild types. These findings demonstrate
that PRL has an inhibitory effect on murine hair cycle events. The pituita
ry PRL regulation of hair follicle cycles observed in seasonally responsive
mammals may be a result of pituitary PRL interacting with a local regulato
ry mechanism.