Objective      To study the expression profile of JNK in hair cycle of the back skin in postnatal mice

and to explore the role of JNK in the regulation of hair cycle.       Methods      Fifty-four female C57BL/6J mice were divided according to the time after birth

with their hair follicles in late development(P1)

anagen phase(P7

P14

P31)

catagen phase (P16) and telogen phase(P21). The expression level of JNK was detected by RT-PCR and the localization of JNK in different stages of hair cycle was tested by Western blotting and immunohistochemical staining (IHC).       Results      The results of RT-PCR showed that JNK1 was expressed strongly in the early anagen phase but weakly in the catagen and telogen phases

while JNK2 was moderately expressed in all stages. The results of one way analysis of variance showed that the JNK1 expression level was significantly higher in the early anagen phase (0.99±0.02) than in the telogen phase (0.30±0.01) (P0.05)

and the JNK2 expression level was significantly lower in the early anagen phase (0.77±0.01) than in the catagen phase (0.97±0.03) (P0.05). The results of Western blotting and RT-PCR are consistent. The IHC results showed that JNK was mainly distributed in the outer root sheath (ORS) and matrix in the anagen phase

and was distributed in the ORS and epithelial cord in the catagen phase. There was no JNK expression in the telogen phase.       Conclusion      JNK

which is a dynamic factor in hair cycle

may be involved in the proliferation and/or differentiation of hair follicle matrix cells in the anagen phase

and may play a role in the apoptosis of hair follicle epithelial cells in the catagen phase.