Plastic adaptation to match the skin colour to the surrounding is key to survival. Two biological responses in skin colour are associated with background adaptation. A fast “physiological response” that aggregates/disperses the pigment organelles of skin chromatophores, and a slow “morphological response” that alters the type and/or density of pigment cells in the skin. Both responses are linked by unknown mechanisms. In this review, we discuss the role in skin colour regulation of two molecules that form part of a hypothalamic‐hypophyseal pathway unique to teleosts, melanin‐concentrating hormone “like” (MCHL) (previously known as MCH), and somatolactin. MCHL neurons project to the neurohypophysis and to the pars intermedia pituitary, where they interact with somatolactin‐expressing cells. With a white background MCHL is released into the circulation to induce rapid melanosome aggregation and skin lightening. Somatolactin is also a fish‐specific peptide whose expression and secretion are altered in organisms adapted chronically to white/black backgrounds, and that regulates morphological pigmentation. We discuss the evidence for a model whereby in teleosts, MCHL and somatolactin provide the previously unknown link between physiological and morphological pigmentation.

中文翻译：

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黑色素浓缩激素和生长乳素。连接生理和形态色素沉着的硬骨鱼特异性下丘脑-垂体轴系统

使皮肤颜色与周围环境相匹配的塑料适应是生存的关键。肤色的两种生物学反应与背景适应有关。聚集/分散皮肤色素细胞色素细胞器的快速“生理反应”，以及改变皮肤色素细胞类型和/或密度的缓慢“形态反应”。这两种反应都通过未知的机制联系起来。在这篇综述中，我们讨论了形成硬骨鱼特有的下丘脑-垂体通路一部分的两种分子在肤色调节中的作用，即黑色素浓缩激素“样”（MCHL）（以前称为 MCH）和生长乳素。MCHL 神经元投射到神经垂体和垂体中间部，在那里它们与表达生长乳素的细胞相互作用。在白色背景下，MCHL 被释放到循环中以诱导快速黑素体聚集和皮肤美白。生长乳素也是一种鱼类特异性肽，其表达和分泌在长期适应白色/黑色背景的生物体中发生改变，并调节形态色素沉着。我们讨论了一个模型的证据，即在硬骨鱼中，MCHL 和生长乳素提供了以前未知的生理和形态色素沉着之间的联系。