Jin Xiaowei, von Gall Charlotte, Pieschl Rick L, Gribkoff Valentin K, Stehle Jorg H, Reppert Steven M, Weaver David R
Laboratory of Developmental Chronobiology, MassGeneral Hospital for Children, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
Mol Cell Biol. 2003 Feb;23(3):1054-60. doi: 10.1128/MCB.23.3.1054-1060.2003.
Two high-affinity, G protein-coupled melatonin receptor subtypes have been identified in mammals. Targeted disruption of the Mel(1a) melatonin receptor prevents some, but not all, responses to the hormone, suggesting functional redundancy among receptor subtypes (Liu et al., Neuron 19:91-102, 1997). In the present work, the mouse Mel(1b) melatonin receptor cDNA was isolated and characterized, and the gene has been disrupted. The cDNA encodes a receptor with high affinity for melatonin and a pharmacological profile consistent with its assignment as encoding a melatonin receptor. Mice with targeted disruption of the Mel(1b) receptor have no obvious circadian phenotype. Melatonin suppressed multiunit electrical activity in the suprachiasmatic nucleus (SCN) in Mel(1b) receptor-deficient mice as effectively as in wild-type controls. The neuropeptide, pituitary adenylyl cyclase activating peptide, increases the level of phosphorylated cyclic AMP response element binding protein (CREB) in SCN slices, and melatonin reduces this effect. The Mel(1a) receptor subtype mediates this inhibitory response at moderate ligand concentrations (1 nM). A residual response apparent in Mel(1a) receptor-deficient C3H mice at higher melatonin concentrations (100 nM) is absent in Mel(1a)-Mel(1b) double-mutant mice, indicating that the Mel(1b) receptor mediates this effect of melatonin. These data indicate that there is a limited functional redundancy between the receptor subtypes in the SCN. Mice with targeted disruption of melatonin receptor subtypes will allow molecular dissection of other melatonin receptor-mediated responses.
在哺乳动物中已鉴定出两种高亲和力的G蛋白偶联褪黑素受体亚型。对Mel(1a)褪黑素受体进行靶向破坏可阻断部分而非全部对该激素的反应，这表明受体亚型之间存在功能冗余（Liu等人，《神经元》19:91 - 102，1997年）。在本研究中，分离并鉴定了小鼠Mel(1b)褪黑素受体cDNA，并对该基因进行了破坏。该cDNA编码一种对褪黑素具有高亲和力的受体，其药理学特征与其作为褪黑素受体的编码一致。Mel(1b)受体被靶向破坏的小鼠没有明显的昼夜节律表型。褪黑素抑制Mel(1b)受体缺陷小鼠视交叉上核（SCN）中的多单位电活动，其效果与野生型对照小鼠一样有效。神经肽垂体腺苷酸环化酶激活肽可增加SCN切片中磷酸化环磷酸腺苷反应元件结合蛋白（CREB）的水平，而褪黑素可降低这种作用。在中等配体浓度（1 nM）下，Mel(1a)受体亚型介导这种抑制反应。在Mel(1a)受体缺陷的C3H小鼠中，在较高褪黑素浓度（100 nM）下出现的残余反应在Mel(1a)-Mel(1b)双突变小鼠中不存在，这表明Mel(1b)受体介导了褪黑素的这种作用。这些数据表明SCN中受体亚型之间的功能冗余有限。对褪黑素受体亚型进行靶向破坏的小鼠将有助于对其他褪黑素受体介导的反应进行分子剖析。
