Molecular Mechanism of Circadian Signal Generation in Mammals

1. 蛋白酪氨酸激酶（PTK）参与昼夜节律的产生。我们发现持续向大鼠脑内注射胰岛素完全消除了昼夜节律。根据这一发现，我们研究了PTK是否真的参与昼夜节律信号产生的问题。在研究过程中，我们从新生大鼠脑中分离出一种新的PTK，并将其命名为CSK。我们发现该酶特异性磷酸化src家族PTKs的c端酪氨酸残基，并抑制后者的活性。我们获得了几条证据，证明CSK可能在神经元分化、免疫调节和癌变中发挥关键作用。我们发现视交叉上核（SCN）中p60^<c-src>的PTK活性表现出每日变化，但我们尚未获得CSK特异性参与这一机制的证据。2. 节律产生与细胞周期的关系。我们从神经元失去增殖能力的成熟大脑中分离出一种细胞周期调节蛋白D型G1细胞周期蛋白。我们现在正在研究细胞周期调节和昼夜节律信号的产生是如何相互联系的。3. 能量代谢的中枢调节。已知SCN大致分为背内侧和腹外侧两部分，蝉鸣钟位于前者，参与昼夜节律周期与环境LD周期同步的视黄下丘脑束投射到后者。我们发现大脑能量供应的调节中心位于后者，并获得证据表明这些功能与昼夜节律信号的产生协同调节。

1. Involvement of protein-tyrosine kinase (PTK) in generation of the circaadian rhythm. We found that continuous infusion of insulin into rat brain eliminated the circadian rhythms completely. From this finding, we examined the problem of whether PTK was really involved in the circadian signal generation. During the course of this investigation, we isolated a new type of PTK from neonatal rat brain and named it CSK. We showed that this enzyme specifically phosphorylates the C-terminal tyrosine residues of src-family PTKs and that it inhibited the latter activities. We obtained several lines of evidence that CSK might play critical roles in neuronal differentiation, immumne regulation and carcinogenesis. We showed that PTK activity of p60^<c-src> in the suprachiasmatic nucleus (SCN) exhibited the daily change, but we have not obtained evidence yet that CSK is specifically involved in this mechanism. 2. Relationship between rhythm generation and cell cycle. We isolated a D type G1 cyclin, a regulatory protein for cell cycle, from matured brain, in which neurons lose their proliferating abilities. We are now examining how cell cycle regulation and circadian signal generation are interconnected. 3. Central regulation of energy metabolism. It is known that the SCN is roughly divided into two parts, the dorsomedial and ventrolateral parts, and that the cicadian clock is located in the former and the retinohypothalamic tract which is involved in synchronization of the circadian period to an environmental LD cycle is projected to the latter. We found that the regulatory center for energy supply to the brain is located in the latter and obtained evidence suggesting that these functions are cooperatively regulated with the circadian signal generation.