Bernard Bruno A
L'Oréal Recherche, Centre C. Zviak, 90 rue du Général Roguet, 92110 Clichy.
J Soc Biol. 2003;197(1):57-61.
The existence of a growth and regeneration cycle makes the hair follicle a true paradigm of tissue homeostasis. Analysis of about 9000 cycles led us to propose a stochastic model of human hair dynamics. The existence of hair cycles implies that stem cells must be cyclically activated and hair melanin unit has to be renewed. Using different markers, we were able to identify two distinct epithelial stem cell reservoirs, located in the upper and lower thirds of the anagen hair follicle outer root sheath. These two reservoirs fuse during the regression phase and individualize again in the new forming anagen hair follicle. Using a set of antibodies specific of melanocyte lineage and melanogenesis, pigmentation unit turnover was followed throughout the entire hair cycle. In the terminal anagen hair, active melanocytes were localized on top of the dermal papilla, while amelanotic melanocytes were identified in the upper third of the outer root sheath (ORS). Those amelanotic melanocytes located in upper ORS probably represented a melanocyte reservoir for successive hair generation, since at the induction of anagen phase, some melanocytes were committed to cell division and melanogenesis was turned on, but only in the nascent hair bulb, close to the dermal papilla.
生长和再生周期的存在使毛囊成为组织稳态的一个真正典范。对约9000个周期的分析使我们提出了一个人类毛发动力学的随机模型。毛发周期的存在意味着干细胞必须被周期性激活，并且毛发黑素单位必须更新。使用不同的标记物，我们能够识别出位于生长期毛囊外根鞘上三分之一和下三分之一处的两个不同的上皮干细胞库。这两个库在退行期融合，并在新形成的生长期毛囊中再次个体化。使用一组针对黑素细胞谱系和黑素生成的特异性抗体，在整个毛发周期中追踪色素沉着单位的更新。在终末生长期毛发中，活跃的黑素细胞位于真皮乳头顶部，而无黑素的黑素细胞在外根鞘（ORS）的上三分之一处被识别出来。那些位于ORS上部的无黑素黑素细胞可能代表了连续毛发生成的黑素细胞库，因为在生长期开始时，一些黑素细胞开始进行细胞分裂并且黑素生成被开启，但仅在靠近真皮乳头的新生毛球中。
