μ-Crystallin, thyroid hormone-binding protein, is expressed abundantly in the murine inner root sheath cells

In an attempt to investigate the genes expressed during the development of mouse hair follicles, we employed RNA differential display and identified a cDNA encoding mu-crystallin, that is a major component of kangaroo lens and a cytosolic NADP-regulated thyroid hormone-binding protein in human kidney. In northern blot study, mu-crystallin transcripts were detected in skin at the highest level among the mouse tissues, whereas lower but detectable in the eye, brain, kidney, heart, lung, and liver. Furthermore, in mouse skin, the gene expression of mu-crystallin followed hair cycle fundamentally, increased significantly during mid- and late anagen phases and decreased during the catagen, telogen, and early anagen phases. In situ hybridization revealed that mu-crystallin gene starts to be activated in hair cone of anagen III, and that in anagen VI, its expression is detected predominantly in the cuticle layer of the inner root sheath from the upper hair bulb to the middle portion of the keratogenous zone and in the Huxley's layer through the keratogenous zone. The expression was not detected in catagen, telogen, and early anagen hair follicles, and any other skin components. These results suggest the possible involvement of mu-crystallin in the development of mouse hair follicles during the anagen phase.