Mechanisms of Circadian Rhythmicity in CLOCK-Deficient Mice

描述（由申请人提供）：昼夜节律存在于整个动物王国的物种中。在人类中，昼夜节律定时障碍导致基于昼夜节律的睡眠障碍、轮班工人和时差期间的适应不良，并且可能导致神经精神障碍，包括抑郁症和季节性情感障碍。转录-翻译反馈环是生物钟机制的中心。已知的驱动昼夜节律转录的正元件是CLOCK和BMAL 1，这两种基本的螺旋环螺旋蛋白，其二聚化以激活响应基因的表达。我们最近培育出了一种带有Clock基因无效突变的小鼠。出乎意料的是，这些时钟缺陷小鼠在恒定条件下保持行为的昼夜节律性。我们的研究将描述时钟缺陷小鼠的生理和分子节律，并评估在没有时钟的情况下节律性的机制。在先前描述的Clock显性负突变的小鼠中，CLOCK-delta 19蛋白可能通过干扰其他关键bHLH-PAS蛋白的活性来破坏昼夜节律，这表明主要的昼夜节律转录激活因子仍有待鉴定。这个项目的一个主要目标将是确定这一明显的第二种转录激活机制。我们将测试的假设，NPAS 2，一个bHLH-PAS转录因子密切相关的时钟，可以取代时钟，从而保持节奏的时钟缺陷小鼠。我们还将确定BMAL 1是否是必要的节奏在没有时钟，期待一个发现，将使研究的基础上评估候选BMAL 1相互作用蛋白的功能重要性。这些拟议的研究对于了解生物钟机制的核心组成部分CLOCK的功能是必要的，因此与理解和可能开发基于昼夜节律的睡眠和精神疾病的新疗法有关。此外，生物钟在调节生殖、代谢、细胞生长和肿瘤进展方面发挥着不同的作用，因此了解生物钟产生的基本机制具有许多意义。

DESCRIPTION (provided by applicant): Circadian rhythms are present in species throughout the animal kingdom. In humans, disorders of circadian timing contribute to circadian-based sleep disorders, maladjustment of shift workers and during jet lag, and may contribute to neuropsychiatric disorders including depression and seasonal affective disorder. A transcriptional-translational feedback loop is at the center of the circadian clock mechanism. The known positive elements driving circadian transcription are CLOCK and BMAL1, two basic helix loop helix proteins that dimerize to activate expression of responsive genes. We have recently generated mice with a null mutation of the Clock gene. Unexpectedly, these CLOCK-deficient mice retain circadian rhythmicity in behavior in constant conditions. Our studies will characterize physiological and molecular rhythms in CLOCK-deficient mice, and assess mechanisms of rhythmicity in the absence of CLOCK. In mice with the previously described dominant negative mutation of Clock, the CLOCK-delta19 protein likely disrupts circadian rhythmicity by interfering with the activity of other key bHLH-PAS proteins, indicating that a major circadian transcriptional activator remains to be identified. A major objective of this project will be to identify this apparent second mechanism for transcriptional activation. We will test the hypothesis that NPAS2, a bHLH-PAS transcription factor closely related to CLOCK, can substitute for CLOCK and thus maintain rhythmicity in CLOCK-deficient mice. We will also determine whether BMAL1 is necessary for rhythmicity in the absence of CLOCK, expecting a finding that will enable studies based on assessment of the functional importance of candidate BMAL1-interacting proteins. The proposed studies are necessary to understand the function of CLOCK, a central component of the circadian clock mechanism, and thus are relevant to understanding and possibly developing novel treatments for circadian-based sleep and psychiatric disorders. In addition, the circadian clock plays diverse roles in regulating reproduction, metabolism, cell growth and tumor progression, so the importance of understanding basic mechanisms of circadian rhythm generation has many implications.