HYALURONAN IS INVERSELY CORRELATED WITH THE EXPRESSION OF CD44 IN THEDERMAL CONDENSATION OF THE EMBRYONIC HAIR FOLLICLE

Previously, we have shown that CD44 (the hyaluronan receptor) was invo lved in the degradation of hyaluronan. In the present study, we examin ed the distribution of CD44 and hyaluronan in the skin of embryonic an d mature mice. During embryonic development, CD44 was prominently expr essed by the condensed mesenchymal cells involved in the formation of the hair follicles, but was absent from the surrounding interstitial c ells. the cells of the dermal condensation expressed CD44 throughout t he development of the hair follicle; however, once the hair follicle r eached maturity, the mesenchymal cells of the dermal papilla no longer expressed this molecule. In contrast to the above, the distribution o f hyaluronan was reversed from that of CD44. Hyaluronan was widespread throughout the embryonic dermis, but was conspicuously absent from th e regions of the dermal condensation. This arrangement persisted throu gh the development of the hair follicle; however, in the mature hair f ollicle, hyaluronan reappeared in the dermal papilla. Thus, in the emb ryonic dermis, the expression of CD44 and hyaluronan were complementar y to each other. However, in the adult skin, only minor changes were d etected in the levels of CD44 and hyaluronan associated with the cells of the dermal condensation during the hair cycle. When organ cultures of embryonic mouse skin were treated with Streptomyces hyaluronidase, the interstitial mesenchymal cells became compacted, indicating that the removal of hyaluronan leads to the condensation of these cells. Th e results of this study are consistent with the hypothesis that the ex pression of CD44 by the inductive mesenchymal cells allows them to deg rade hyaluronan in a localized region, leading to formation and mainte nance of the dermal condensation.