Human skin melanin pigmentation is regulated by systemic and local factors. According to the type of melanin produced by melanocytes, the transfer and degradation of melanosomes differ, thus accounting for most variations between ethnicities. We made the surprising observation that in a drastically changed environment, white and black phenotypes are reversible since Caucasian skin grafted onto nude mice can become black with all black phenotypic characteristics. Black xenografts differed essentially from other grafts by the levels of epidermal FGF-2 and keratin 5. In vitro analysis confirmed that FGF-2 directly regulates keratin 5. Interestingly, this phenomenon may be involved in human pathology. Keratin 5 mutations in Dowling-Degos Disease (DDD) have already been associated with the pheomelanosome-eumelanosome transition. In a DDD patient, keratin 5 was expressed in the basal and spinous layers, as observed in black xenografts. Furthermore, in a common age-related hyperpigmentation disorder like senile lentigo (SL), keratin 5 distribution is also altered. In conclusion, modulation of keratin 5 expression and distribution either due to mutations or factors may account for the development of pigmentary disorders.

中文翻译：

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表皮角蛋白5的表达和分布受皮肤的影响。

人体皮肤黑色素的色素沉着受全身和局部因素的调节。根据黑素细胞产生的黑色素的类型，黑素体的转移和降解不同，因此可以解释种族之间的大多数差异。我们做出了令人惊讶的观察，在急剧变化的环境中，白色和黑色表型是可逆的，因为嫁接到裸鼠上的高加索皮肤可以变成具有所有黑色表型特征的黑色。黑色异种移植物与其他移植物的本质区别在于表皮FGF-2和角蛋白5的水平。体外分析证实FGF-2直接调节角蛋白5。有趣的是，这种现象可能与人类病理有关。Dowling-Degos病（DDD）中的角蛋白5突变已经与表皮粒体-黑素体转变有关。在DDD患者中，如在黑色异种移植物中所观察到的，角蛋白5在基底层和棘层中表达。此外，在常见的与年龄相关的色素沉着过度疾病中，如老年性扁豆（SL），角蛋白5分布也会改变。总之，由于突变或因素导致的角蛋白5表达和分布的调节可能是色素性疾病发展的原因。