Featured Article: Circadian [Ca2+]c Waves & Long-range Network Connections in Rat Suprachiasmatic Nucleus

Featured Article: Circadian [Ca2+]c Waves and Long-range Network Connections in Rat Suprachiasmatic Nucleus

Featured article of EJN issue 35-9: Circadian [Ca2+]c Waves and Long-range Network Connections in Rat Suprachiasmatic Nucleus

Jin Hee Hong, Byeongha Jeong, Cheol Hong Min, and Kyoung J. Lee
Center for Cell-dynamics and Department of Physics, Korea University, Seoul, Korea

The suprachiasmatic nucleus (SCN) is the master clock in mammals governing the daily physiological and behavioral rhythms. It is composed of thousands of clock cells with their own intrinsic periods varying over a wide range (20~28 h). Despite this heterogeneity, an intact SCN maintains a coherent 24 h periodic rhythm through some cell-to-cell coupling mechanisms. This study examined how the clock cells are connected to each other and how their phases are organized in space by monitoring the cytosolic free calcium ion concentration of clock cells using the calcium binding fluorescent protein, cameleon. Extensive analysis of 18 different organotypic slice cultures of SCN showed that the SCN calcium dynamics is coordinated by phase-synchronizing networks of long-range neurites as well as by diffusively propagating phase waves. The networks appear quite extensive and far-reaching, and the clock cells connected by  them exhibit heterogeneous responses in their amplitudes and periods of oscillation to  TTX treatments. Taken together, our study suggests that the network of long-range  cellular connectivity has an important role for SCN achieving its phase and period coherence.

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Commentary
Read the corresponding commentary by Rae Silver on this article: Phase Waves in the Suprachiasmatic Nucleus.


EJN News Supplemental Figures (not peer-reviewed)

Upper panel is a schematic diagram illustrating the phase relationships and sub-networks of clock cells in a model SCN. The small arrows represent a specific circadian phase of a clock cell (small disk), while the large arrows represent the local mean of the phases. The yellow colored disks represent cameleon-expressing clock cells. Clock cells are not only diffusively coupled but also have long-range direct connections (yellow lines). Lower panel shows a typical YFP fluorescent image of a SCN slice culture expressing cameleon protein(3V: 3rd ventricle; OC: optic chiasm). A gene-gun was used for transfecting cameleon cDNA.

Upper panel is a schematic diagram illustrating the phase relationships and sub-networks of clock cells in a model SCN. The small arrows represent a specific circadian phase of a clock cell (small disk), while the large arrows represent the local mean of the phases. The yellow colored disks represent cameleon-expressing clock cells. Clock cells are not only diffusively coupled but also have long-range direct connections (yellow lines). Lower panel shows a typical YFP fluorescent image of a SCN slice culture expressing cameleon protein(3V: 3rd ventricle; OC: optic chiasm). A gene-gun was used for transfecting cameleon cDNA.

 

 


Biographical notes

  Jin Hee Hong received her PhD degree in Neurophysiology in the Department of Life Sciences at Ewha Womans University and started this research project as a postdoctoral fellow in the laboratory of Kyoung Jin Lee.  Her current research interest is to understand the dynamics of cytosolic calcium concentration and the network properties in SCN as related to the circadian rhythm generation, synchronization, and phase coherence.
   Byeongha Jeong graduated with BS/MS degrees from the Department of Physics at Korea University and is currently working for his PhD degree in the laboratory of Kyoung Jin Lee.  He has built a cameleon FRET imaging system and developed various image data analysis software.  His major research concern is to find the relationship between the level of cytosolic calcium and that of clock genes, and understand their spatiotemporal wave dynamics.
  Cheol Hong Min graduated with BS degree from the Department of Physics, Korea University.   As a PhD candidate, he belongs to the calcium dynamics group in Kyoung Jin Lee’s lab.  He was involved in the studies investigating the origin of calcium puffs (transients) in SCN as well as in cultured networks of astrocytes.
His current work is to decipher the mechanism responsible for the recurrent calcium waves in cultures of astrocytes.
 Kyoung J. Lee is currently the director of the Center for Cell Dynamics (CND) and full professor in the Department of Physics at Korea University in Seoul.   He got his doctoral degree in physics (nonlinear dynamics) at the University of Texas at Austin in 1994 and got interested in biology beginning his postdoctoral career in Princeton University.   Since then, he worked on various issues like cardiac wave instabilities, learning and memory of neural networks, cell motility and swarming, and circadian clock.  Broadly speaking, he is interested in biophysical problems in which nonlinear dynamics and physics of complexity play an important role.

 

 

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