Section on Light and Circadian Rhythms

2019年财政年度的研究项目可分为以下四个主要领域： 1-ipRGCs的多样性和功能 我们已经产生了转基因小鼠系，以揭示固有的光敏视网膜神经节细胞(IpRGC)和相应的大脑电路对内部生物钟与太阳日同步的贡献。我们有一些动物要么只有交叉上核(SCN)投射的ipRGCs(Chen等人，《自然》2011)，要么缺乏投射到SCN的ipRGC(未发表)。这将使我们能够确定个别亚型的ipRGC对昼夜节律光携带和相移的贡献。昼夜节律振荡器的相位可以被称为相移的剧烈光脉冲提前或延迟。我们令人兴奋的初步数据显示，不同的ipRGC群体控制着昼夜节律振荡器中的相位延迟与相位推进。这一发现挑战了该领域目前的观点，即类似的机制是相位推进和相位延迟的基础，而且光对时钟有简单的开/关效应。未来的研究将确定哪些ipRGC群体对于推进和延迟是必要的，并绘制受光影响的大脑区域，以引起昼夜节律振荡器的相位变化。 我们最近有了一个惊人的发现，即ipRGC的一个亚群(200个M1-Brn3b阴性，我们称之为昼夜节律光感受器)对生物钟和视觉的发育至关重要，尽管它们不投射到视觉中心(Chew等人，eLife 2017)。一个令人兴奋的假设是，这200个ipRGC(Chen等人，《自然》2011)代表了一个进化的古老的光感受器类别，因为它们对几种不同的行为(光携带、时钟和视觉的发育以及局部瞳孔的光反射)产生了广泛的影响。因此，了解这一群体相对于其他ipRGC和常规神经节细胞的分子和功能特征是至关重要的。因此，我们已经开始使用壁内测序设施来检查这个群体的转录组和表观遗传标记。该项目将提供分子手柄，以了解200个M1 ipRGC相对于其他ipRGC和传统神经节细胞的个体发育和功能特化。这项研究是与约翰·霍普金斯大学医学院的亚历克斯·科洛德金斯实验室合作完成的。 2-揭示光对情绪、学习和记忆的影响所在的视网膜和大脑回路 众所周知，光疗法可以用来治疗人类几种类型的严重抑郁症。然而，很难确定光的这些效应是否纯粹是安慰剂效应。我们最近发现了一个新的大脑区域，可以让光线直接调节啮齿动物的情绪。这个新的区域被称为缰核周围复合体，它连接着大脑中几个对情绪调节至关重要的区域，如内侧前额叶皮质和伏隔核。这项研究已发表在《细胞》(Fernandez et.并与Chudasama博士和Merikangas实验室建立了未来的合作关系，以确定是否在包括人类在内的灵长类动物中发现了该区域。 在同一篇论文中，我们还表明，光对学习和记忆的影响需要SCN，特别是Brn3b阴性的ipRGC。这是光对情绪的影响和对学习的影响之间的显著区别。令人难以置信的是，SCN并没有起到中央起搏器的作用，而只是将光信息传递到海马体。下一步工作的目的是弄清楚这个电路(S)。 3-确定光线如何通过直接途径或通过昼夜光携带机制影响睡眠和体温调节。 在体温调节和睡眠领域，一个悬而未决的问题是，昼夜节律光携带所需的光是否使用与光对这两个功能的剧烈影响所需的光相同的电路。我们在这项研究中使用了小鼠(Rupp et.ELife 2019)，这意味着与人类的警觉和体温升高相比，光能显著诱导睡眠和体温降低。我们发现，投射到SCN的Brn3b阴性的ipRGC足以调节体温和睡眠节律。值得注意的是，这些细胞不能诱导光线对这两种功能的急性影响。事实上，我们表明投射到SCN的ipRGC以外的细胞是必需的(Rupp et.等人，eLife 2019)。未来的研究将致力于确定急性光照对体温和睡眠产生影响所需的大脑区域。 4-作为协作的其他项目 另外三个项目作为合作项目发表。首先，与吉村博士在日本的团队合作，我们证明了一种新的神经抑制素5在紫外线刺激下的昼夜节律光携带中具有作用。其次，在约翰·霍普金斯大学约翰斯顿博士的实验室里，我们的合作者Kiara Eldred能够在培养中产生人类视网膜，并找出产生蓝色和红色/绿色视锥的途径。第三，与迈阿密大学的帕克斯博士实验室合作，我们找出了为什么ipRGC比其他RGC更能抵抗细胞死亡，具有更好的再生能力。 共同努力，我们将继续在环境光信号如何调节几种对人类福祉至关重要的功能方面开辟新的天地。

Research projects, Fiscal Year 2019, can be divided into four major areas listed below: 1- Diversity and function of ipRGCs We have generated genetically modified mouse lines to uncover the contribution of intrinsically photosensitive retinal ganglion cells (ipRGCs) and the corresponding brain circuits to the synchronization of the internal biological clock to the solar day. We have animals that either harbor only the suprachiasmatic nucleus (SCN)-projecting ipRGCs (Chen et al., Nature 2011) or lack the ipRGCs that project to the SCN (unpublished). This will allow us to determine the contribution of individual subtypes of ipRGCs to circadian photoentrainment and phase shifts. The phase of the circadian oscillator can be advanced or delayed by acute pulses of light, known as phase shifts. Our exciting preliminary data reveal that different populations of ipRGCs control phase delays versus phase advances in the circadian oscillator. This finding challenges the current view in the field that similar mechanisms underlie phase advances and phase delays, and that light has a simple on/off effect on the clock. Future studies will determine which ipRGC populations are necessary for advances versus delays, and map the brain regions that are influenced by light to cause changes in the phase of the circadian oscillator. We recently made a startling discovery that a subpopulation of ipRGCs (200 M1-Brn3b-negative, which we called circadian photoreceptors) is critical for the development of the circadian clock as well as vision, although they do not project to visual centers (Chew et al., eLife 2017). An exciting hypothesis is that these 200 ipRGCs (Chen et al., Nature 2011) represent an evolutionary ancient photoreceptor class given their broad influence on several distinct behaviors (photoentrainment, development of the clock and vision as well as local pupillary light reflex). Therefore, it is critical to understand the molecular and functional specification of this population in relation to other ipRGCs and conventional ganglion cells. Thus, we have started to examine the transcriptome and epigenetic marks of this population by using the intramural sequencing facilities. This project will provide the molecular handles to understand the ontogeny and the functional specialization of the 200 M1 ipRGCs in relation to other ipRGCs and conventional ganglion cells. This is being done in collaboration with Alex Kolodkins lab at the Johns Hopkins University-School of Medicine. 2- Uncovering the retinal and brain circuits that underlies the influence of light to mood and learning and memory It is well established that light therapy can be used to treat several types of major depression in humans. However, it has been hard to ascertain whether these effects of light are purely placebo effects. We recently discovered a new brain region that allows light to directly regulate mood in rodents. This new region is termed the perihabenular complex and it connects to several areas in the brain essential for mood regulation such as the medial prefrontal cortex and the nucleus accumbens. This work has been published in Cell (Fernandez et. al., Cell 2018) and future collaborations are established with both Drs. Chudasama and Merikangas labs to determine if this region is found in primates, including humans. In the same publication, we also showed that the influence of light on learning and memory requires the SCN and specifically the Brn3b-negative ipRGCs. This is a remarkable separation between light effects on mood and learning. Incredibly, the SCN is not acting as a central pacemaker, but simply as a relay for light information to the hippocampus. Future work is aimed at figuring out this circuit(s). 3- Determining how light influences sleep and body temperature regulation through a direct pathway or through the circadian photoentrainment mechanism. An unanswered question in the fields of body temperature regulation and sleep is whether, light required for circadian photoentrainment uses the same circuits as light required for the acute effects of light on these two functions. We used mice in this study (Rupp et. al., Elife 2019), which are nocturnal, which means that light induces sleep and lower body temperature acutely as compared to alertness and increase in body temperature in humans. We discovered that the Brn3b-negative ipRGCs that project to the SCN are sufficient for photoentraining both body temperature and sleep rhythms. Remarkably, these cells are not capable of inducing acute effects of light on either function. In fact, we show that cells other than the ipRGCs that project to the SCN are required (Rupp et. al., Elife 2019). Future studies will aim to define the brain regions required for the acute light effects on body temperature and sleep. 4- Other projects as collaborations Three other projects were published as collaborations. First, with Dr. Yoshimuras group in Japan, we showed that a new neuropsin 5 has a role in circadian photoentrainment under UV light stimulations. Second, with Dr. Johnstons lab at the Johns Hopkins University, our Co-student, Kiara Eldred, was able to generate human retina in culture and figure out the pathway by which blue versus red/green cones are generated. Third with Dr. Parks lab at the University of Miami, we figured out why ipRGCs are more resistant to cells death and have better regenerating abilities compared to other RGCs. Together, we will continue to break new ground about how light signaling from the environment regulates several functions that are essential for the well-being of humans.