How are mammalian circadian rhythms affected? The study found new neuronal subtypes.

Circadian rhythm, which exists widely in nature, plays an important role in regulating many physiological processes such as exercise, sleep, metabolism and so on.in human society, circadian rhythm disorder can lead to various diseases including sleep disorders. Therefore, it is of great significance for human health to understand how circadian rhythm occurs, maintain and play a role in the nervous system.what controls the circadian rhythm of mammals? In fact, the suprachiasmatic nucleus of the brain, like a prism, converts light signals into rhythmic signals, and different neurons produce different phases of oscillation, just as sunlight refracts into a sundial and displays different hours.on February 18, 2020, a research paper entitled "spatiotemporal single cell analysis of gene expression in suprachiasmatic nucleus of mice" was published online in the journal Nature Neuroscience.in this study, we systematically classified the cells in the suprachiasmatic nucleus (SCN), the circadian rhythm center of mice, by using single cell sequencing technology, and found new neuronal subtypes, revealing the differences of gene expression of these cell subtypes in the process of circadian rhythm and light stimulation. At the same time, the three-dimensional spatial distribution of each subtype cell was completely reconstructed at the single cell level The neural mechanism of circadian rhythm in animals has laid an important foundation.the study was completed by the center for excellence and innovation of brain science and intelligent technology, Chinese Academy of Sciences (Institute of Neuroscience), Shanghai brain science and brain like research center, and Yan Jun research group of State Key Laboratory of neuroscience.current studies suggest that the suprachiasmatic nucleus (SCN) in the brain plays an important role.SCN can receive the light and dark signals from the retina, generate the circadian rhythm oscillation, and transmit the rhythm signal to the whole body.at the molecular level, circadian rhythm is generated by a series of transcription translation feedback loops (ttfl) composed of a series of core rhythm genes.previous studies have shown that the expression of core rhythm genes in SCN neurons shows synchronous oscillation, and cells in different spatial positions have different oscillation phases.studies have shown that SCN cells express a variety of neuropeptides and receptors, and their intercellular communication network is an important basis for synchronization of gene expression in SCN cells.previous studies on SCN only focused on the cells expressing VIP and AVP. However, it is not clear about the comprehensive cell types of SCN, the spatial distribution of different cell types in SCN, and how these cell types play a role in circadian rhythm.the Yanjun research group used drop SEQ, single molecule fluorescence in situ hybridization (smfish) and laser microdissection sequencing (LCM SEQ) to analyze mouse SCNS sampled at different time points of day and night. The transcriptome was used to systematically classify the SCN cells and obtain the gene expression rhythm in different cell types, and reconstruct these cells The 3D spatial position information of type in SCN.the study first found that all kinds of non neuronal cells, including ependymal cells, glial cells, and so on, had extensive expression of rhythm genes, which implied that all kinds of cells in SCN had cell-specific rhythmic function.interestingly, the oscillatory phase of core rhythm genes in all non neuronal cells was significantly later than that in neurons.A: five subtypes of SCN neurons were obtained by single cell sequencing.b: smfish showed the co labeling results of marker genes of SCN neuronal subtypes. C: rhythmic gene expression in five SCN neuronal subtypes. the pictures in this paper are provided to the center for excellence and innovation of brain science and intelligent technology of Chinese Academy of Sciences (Institute of Neuroscience). D: three dimensional spatial distribution of SCN neuronal subtypes obtained by transparent imaging. e: three dimensional expression of genes in SCN obtained from LCM SEQ. F: this picture implies that SCN, as the core pacemaker of biological rhythm, converts light signals into rhythmic signals and produces oscillations of different phases, which are refracted to different times on ancient Chinese sundials. in neurons, SCN neurons had significantly higher core gene expression than non SCN neurons. the research group further divided the neurons in SCN into five subtypes, which were named AVP + / NMS +, GRP + / VIP +, VIP + / NMS +, CK + / c1ql3 + and CK + / BDNF + (Fig. a-b). among them, AVP + / NMS +, VIP + / NMS + and CCK + / c1ql3 + showed strong expression of rhythm genes (Fig. C). the phase of rhythm gene expression in AVP + / NMS + cells on the dorsal side of SCN and VIP + / NMS + cells on the ventral side was prior to that of CK + / c1ql3 + cells in front of SCN. through the light stimulation experiment, we found that there were significant differences in the response of different SCN neuronal subtypes to light, among which GRP + / VIP + cells had the strongest response to light, while CK + / c1ql3 + and CK + / BDNF + cells had the weakest response to light. this shows that SCN neuronal subtypes have functional differentiation in the generation of rhythmic oscillations and light sensitivity. finally, the three-dimensional spatial distribution of SCN neuronal subtypes in SCN was reconstructed by tissue transparence imaging (Fig. d), and the gene expression gradient in SCN was revealed by laser microdissection combined with RNA sequencing (Fig. E), which provided further evidence for the classification of SCN cell subtypes and spatial anisotropy in function. in this study, advanced single cell technology was used to comprehensively classify, reconstruct and analyze the SCN of circadian rhythm Center for the first time. The information of different cell types, spatiotemporal gene expression of neuron subtypes, and cellular architecture of SCN were obtained, which provided important clues for studying the neural mechanism of circadian rhythm in mammals. this work can be summarized by f-diagram, implying that SCN, as the core pacemaker of biological rhythm, converts light signals into rhythmic signals like a prism, and different neurons produce different phases of oscillation, which refract to different times on ancient Chinese sundials. in human society, circadian rhythm disorder can lead to various diseases including sleep disorders. Therefore, it is of great significance for human health to understand how circadian rhythm occurs, maintain and play a role in the nervous system. under the guidance of researcher Yan Jun, this work is mainly completed by doctoral students Wen shaoang and Ma Danyi. At the same time, research assistants Zhao Meng, Wu QingQin and fan Yuqi, doctoral students Xie Lucheng and Zhu Chuanzhen, senior engineer Wang Haifang, and postdoctoral Gou Lingfeng also made important contributions. this work is supported by the strategic leading science and technology program of Chinese Academy of Sciences, Shanghai Science and technology major project, general program of National Natural Science Foundation of China, National Natural Science Foundation of China and young scientists program of Shanghai Science and Technology Commission.