Takahashi Akiyoshi, Kobayashi Yuki, Amano Masafumi, Yamanome Takeshi
School of Marine Biosciences, Kitasato University, Ofunato, Iwate 022-0101, Japan.
Peptides. 2009 Jul;30(7):1374-82. doi: 10.1016/j.peptides.2009.04.014. Epub 2009 May 3.
Proopiomelanocortin (POMC) is a precursor of adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormone (MSH), and endorphin (END). We have characterized POMC systems in barfin flounder. The results revealed unique aspects of POMC systems. Notable features in terms of pituitary functions are the occurrence of three functional POMC genes, the mutation of an essential sequence in the beta-END in one of the genes, occurrence of alpha-MSH in addition to ACTH in the pars distalis of the pituitary, and expression of the three genes in a single cell. While MSHs stimulate pigment dispersion, expression of the POMC gene and plasma levels of MSH do not always respond to background color changes between black and white. The functions of MSHs in skin pigmentation are very unique, because acetylation at the N-terminal of alpha-MSH inhibits its pigment dispersing activity. This is in contrast to results from other teleosts and amphibians, in which acetylation increases the activity. In the skin, the POMC gene is expressed in the non-chromatophoric dermal cells, indicating that MSH produced in the skin de novo has a paracrine function. The detection of MSH peptides in skin extracts seems to show that the control of skin pigmentation by MSHs is twofold-endocrine control by the pituitary, and paracrine control by the skin itself. Thus, fish provide an interesting model to help understand the structural and functional diversity of POMC systems. In this review, we provide an overview of our recent studies on the characterization of molecules and biological significance of POMC systems in barfin flounder.
阿黑皮素原（POMC）是促肾上腺皮质激素（ACTH）、促黑素细胞激素（MSH）和内啡肽（END）的前体。我们已经对条石鲷中的POMC系统进行了表征。结果揭示了POMC系统的独特方面。就垂体功能而言，显著特征包括存在三个功能性POMC基因、其中一个基因的β-END中一个关键序列的突变、垂体远侧部除了ACTH外还存在α-MSH以及三个基因在单个细胞中的表达。虽然MSH刺激色素扩散，但POMC基因的表达和MSH的血浆水平并不总是对黑白背景颜色变化做出反应。MSH在皮肤色素沉着中的功能非常独特，因为α-MSH N端的乙酰化会抑制其色素扩散活性。这与其他硬骨鱼和两栖动物的结果相反，在其他硬骨鱼和两栖动物中，乙酰化会增加活性。在皮肤中，POMC基因在非色素细胞的真皮细胞中表达，这表明皮肤中从头产生的MSH具有旁分泌功能。在皮肤提取物中检测到MSH肽似乎表明，MSH对皮肤色素沉着的控制是双重的——垂体的内分泌控制和皮肤自身的旁分泌控制。因此，鱼类为帮助理解POMC系统的结构和功能多样性提供了一个有趣的模型。在这篇综述中，我们概述了我们最近关于条石鲷中POMC系统的分子表征和生物学意义的研究。
