Last updated on 29 July, 2011.
Seminar
Department of Biophysics and Biochemistry Seminar by Dr. Lamb (25, July, 2011)
Department of Biophysics and Biochemistry Seminar by Dr. Obara (25, December, 2010)
Department of Biophysics and Biochemistry Seminar by Dr. Kim (13, December, 2010)
Department of Biophysics and Biochemistry Seminar by Dr. Whitmore (8, November, 2010)
Department of Biophysics and Biochemistry Seminar by Dr. Hatter (4, June, 2010)
Department of Biophysics and Biochemistry Seminar by Dr. Storm (14, September, 2009)
Department of Biophysics and Biochemistry Seminar by Dr. Klein (1, June, 2009)
Department of Biophysics and Biochemistry Seminar by Dr. Brown (6, March, 2009)
Department of Biophysics and Biochemistry Seminar by Dr. Albrecht (13, November, 2008)
Department of Biophysics and Biochemistry Seminar by Dr. Hardin (15, July, 2008)
Department of Biophysics and Biochemistry Seminar by Dr. Lamb (25, July, 2011)
Theme : Phototransduction in rods and cones of the vertebrate retina
Dr. Trevor D. Lamb
John Curtin School of Medical Research, and ARC Centre of Excellence in Vision Science, Australian National University, Canberra, ACT 0200, Australia
The rod and cone photoreceptor cells of the vertebrate retina transduce light into a neural signal using closely similar cellular and molecular mechanisms, though with a number of subtle differences that together endow the cell types with distinctive functional properties. Cones mediate vision over most light levels, providing relatively high-speed responses; importantly, they adapt over an enormously wide range of light intensities and never saturate during steady illumination. Rods operate under extremely low light conditions, and reliably detect individual photons of light; they saturate once the intensity of illumination exceeds twilight levels.
The molecular mechanism of transduction in vertebrate photoreceptors is understood in detail. Light-activated rhodopsin catalyses the activation of the G protein transducin, which in turn activates a PDE, thereby hydrolysing cyclic GMP and closing ion channels in the plasma membrane and shutting-off the “dark current” of cations. Using this knowledge it is possible to predict the waveform of the photoreceptor’s response to light.
Rods and cones differ anatomically, in the topology of the outer segment membrane. In addition there are differences in the proteins of phototransduction. Some of these proteins are expressed as rod- and cone-specific isoforms, whereas others are identically the same protein in rods and cones; in addition, the expression levels may differ significantly between rods and cones.
For some of these differences in cellular and molecular make-up of rods and cones, it is possible to predict differences in functional properties of the cell types. Soon it may be possible to account for all of the physiological differences betweens rods and cones.Lamb, T.D. & Pugh, E.N. Jr (2006). Phototransduction, dark adaptation, and rhodopsin regeneration. The Proctor Lecture. Invest. Ophthalmol. Vis. Sci. 47, 5138-5152.
Lamb, T.D., Collin, S.P. & Pugh, E.N. Jr (2007). Evolution of the vertebrate eye: Opsins, photoreceptors, retina, and eye-cup. Nat. Rev. Neurosci. 8, 960-975.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Obara (25, December, 2010)
Theme : The Basal body protein Wtip regulates cilia mediated processes by modulating non-canonical Wnt signaling
Dr. Tomoko Obara
Dept. of Cell Biology University of Oklahoma Health Science Center Oklahoma City, OK 73104, USA
Cilia are antennae-like organelle characterized by the presence of nine peripheral doublets of microtubules. They originate from the basal body, which is located just below the cell surface and is analogous to the centrioles. In the past few years the importance of cilia has been realized by the observation that many gene products mutated in human diseases are localized in the cilia and/or basal bodies/centrosomes. These so called ciliopathies share some common and unexpected clinical phenotypes such as polycystic kidney disease, nephronophthisis, Senior-Loken syndrome type5, orofaciodifital syndrome type I and Bardet-Biedl syndrome which made refocused to our understanding of various human diseases. Unfortunately, many of the underlying cellular signaling events still remain unclear.
Wilm Tumor suppressor gene (Wt1) interacting protein (Wtip) maps to human chromosome 19, a region linked to familial focal segmental glomerulosclerosis (FSGS). It contains three LIM and a PDZ binding domain. However, the precise in vivo function of the Wtip is still unknown. To elucidate the function of Wtip, we studied its function during the zebrafish embryonic development.
Unexpectedly, zebrafish Wtip protein was found to localize in the basal bodies/centrosomes. Using MO-mediated knockdown, wtip morphants revealed kidney cyst formation accompanied by cloaca obstruction, hydrocephalus, body axis curvature and heart edema, which are similar to our previous studies in the pkd2 morphants. We further characterized the phenotype in the pronephros and found out that Wtip is required to maintain planar cell polarity (PCP), cilia length, numbers and cilia proteins trafficking defects for Polycysin-2 and Ift88. In addition to the kidney defects, we also discovered that loss of wtip results left-right asymmetry and conversion extension cell movement defects such as widened rhombomeres, somites and a shortened body axis due to KV defects such as cilia length, number, KV’s cell shape accompanied by a defect in centrosome migration to the apical cell surface. Moreover, we explored whether these phenotypes caused by loss of wtip are due to PCP signaling, by analyzing potential association to the core PCP and basal body protein Vangl2 which is essential to maintain actin organization. Based on these data we propose that Wtip may provide a new player in ciliopathies modulating non-canonical Wnt signaling.
Organizer : Daisuke Kojima
Department of Biophysics and Biochemistry Seminar by Dr. Kim (13, December, 2010)
Theme : BioClock: From Molecule to Behavior
Dr. Kyungjin Kim
Department of Biological Sciences and Brain Research Center for the 21st Century Frontier Program in Neuroscience, Seoul National University, Seoul 151-742, Korea
Central clock resides in the suprachiamatic nucleus (SCN) of the hypothalamus. Recent studies using genetic and molecular approaches have disclosed fundamental features of molecular circadian clockwork and the network of transcription-translation feedback loops of clock machinery functions not only in the SCN, but also in peripheral clocks in most peripheral tissues. I will discuss our recent findings with two different topics: 1) Adrenal peripheral clock: Adrenal gland has its own intrinsic clock and the peripheral clockwork is tightly linked to steroidogenesis by a StAR(steroidogenic acute regulatory protein). Examination with transgenic mice harboring the adrenal-specific disruption of clock machinery shows that the adrenal clock controls rhythmic StAR expression and glucocorticoid production. The adrenal local clock appears to play an important role in harmonizing circadianphysiology and behavior. 2) Ultradian rhythm of GnRH (Gonadotropin-Releasing Hormone) gene expression: Although pulsatile GnRH secretion from the hypothalamus is reported to be associated with the oscillatory GnRH gene expression, the cellular and molecular mechanism underlying the so-called ‘GnRH pulse generator’ remains to be explored. We generated transgenic mice carrying the rat GnRH promoter-driven destabilized luciferase reporter (GnRH-dsLuc), and monitored the GnRH promoter activity in individual GnRH neurons derived from postnatal hypothalamic slices by using a real-time bioluminescence recording system. GnRH gene expression is quite irregular, but shows robust ultradian oscillation in a cell-intrinsic manner. In vitro administration of kisspeptin, a potent neuropeptide of GnRH neurons amplifies pulsatile GnRH gene expression by augmenting the pulse amplitude. More importantly, rhythmic treatment of the kisspeptin synchronizes the regular oscillatory GnRH gene expression in the hypothalamus.
- Son GH et al. 2008. Adrenal peripheral clock controls the autonomous circadian rhythm of glucocortioid by causing rhythmic steroid production.
PNAS 105:20970-5.
- Lee Y et al. 2010. Coactivation of the CLOCK-BMAL1 complex by CBP mediates resetting of the circadian clock.
J Cell Sci. 123:3547-3557.
- Lee J et al. 2008. Dual modification of BMAL1 by SUMO2/3 and ubiquitin promotes circadian activation of CLOCK/BMAL1 complex.
Mol Cell Biol. 28:6056-65.
- Shim HS et al. 2007. Rapid activation of CLOCK by Ca2+-dependent protein kinase C mediates resetting of the mammalian circadian clock.
EMBO Rep. 8:366-71.
- Kwon I et al. 2006. BMAL1 shuttling controls transactivation and degradation of the CLOCK/BMAL1 heterodimer.
Mol Cell Biol. 26:7318-30.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Whitmore (8, November, 2010)
Theme : Clock control of cell division: intimate links in zebrafish
Dr. David Whitmore
Deptment of Cell and Developmental Biology, University College London, London, UK
Zebrafish are a useful model for the study of clock function, not least because they possess robust circadian oscillators within most of their tissues and cells. These tissues are themselves directly light responsive, and so the fish clock system appears to be highly decentralized with little, if any, need for a central, master clock, as in mammals. This light responsive property is also found in zebrafish cell lines, making them a unique system with which to study clock function. In addition, zebrafish are an excellent system to study the development of the circadian clock, as large numbers eggs are fertilized and develop outside the female, providing a major advantage to embryonic studies in mammals. Data relating to clocks in cell lines and during embryo development will be discussed further in this seminar. In contrast, we will describe new data regarding clock function in Astyanax mexicanus, the blind Mexican cavefish, and discuss some of the changes that have occurred following evolution in the dark. Another issue of significant interest relates to what cell biological processes the clock itself controls; what are the rhythmic, clock controlled outputs in zebrafish? Dr Tamai will present new data describing the very close molecular connection between the zebrafish clock and control of the cell cycle. In zebrafish cells and embryos, the clock drives very robust rhythms in both S- and M-phase timing of the cell cycle through the rhythmic regulation of key cell cycle regulators.
Dekens, M.P. and Whitmore, D. Autonomous onset of the circadian clock in the zebrafish embryo. (2008) EMBO J. 27: 2757-65.
Tamai, T.K., Young, L.C., and Whitmore, D. Light signalling to the zebrafish circadian clock by Cryptochrome 1a. (2007) PNAS 104: 14712-14717.
Carr, A.J. and Whitmore, D. (2005) Imaging of single light responsive clock cells reveals fluctuating free-running periods. Nat. Cell Biol. 7: 319-321.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Hatter (4, June, 2010)
Theme : Rod photoreceptor retinal circuits impinge on melanopsin ipRGCs for influencing circadian photoentrainment
Dr. Samer Hattar
Assistant Professor Departments of Biology and Neuroscience (JHMI), Johns Hopkins University (Baltimore, USA)
The discovery of atypical ganglion cell photoreceptors (melanopsin containing intrinsically photosensitive retinal ganglion cells; ipRGCs) in the mammalian retina has greatly advanced our understanding of how light influences several non-image forming visual functions independent of image formation. Some of the non-image forming functions are the adjustment of our internal circadian rhythms to the solar day, which influence our mood, alertness and even learning and memory. We have studied extensively the contribution of outer retinal photoreceptors to the regulation of circadian photoentrainment. We find that rods are the predominant photoreceptor type responsible for circadian photoentrainment from the outer retina, with cones playing a minor role in this function. We further determine how the rod photoreceptors send this information to ipRGCs at different light intensities. Our data reveal an unappreciated role for rods in circadian photoentrainment and determine the retinal circuits of how this response is achieved.
Güler AD, Ecker JL, Lall GS, Haq S, Altimus CM, Liao HW, Barnard AR, Cahill H, Badea TC, Zhao H, Hankins MW, Berson DM, Lucas RJ, Yau KW, Hattar S. (2008) Melanopsin cells are the principal conduits for rod-cone input to non-image-forming vision. Nature 453, 102-5.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Storm (14, September, 2009)
Theme : The Role of Signal Transduction Cross-Talk
Dr. Daniel R. Storm
Department of Pharmacology, The University of Washington, Seattle, USA
The central nervous system has the remarkable capacity to process and store enormous amounts of information. Consequently, there is intense interest in molecular and cellular mechanisms underlying the formation and persistence of memory. One of the transcriptional pathways required for consolidation of hippocampus-dependent memory is CRE-(cAMP, Ca2+, Response, Element) mediated transcription. Although a number of signal transduction systems contribute, calmodulin (CaM)-stimulated adenylyl cyclases and Erk/MAP kinases (MAPK) play a major role in Ca2+ activation of CRE-mediated transcription in neurons during formation of memory. Our lab has discovered that the nuclear translocation and activation of MAPK in neurons during contextual memory formation depends upon CaM-stimulated adenylyl cyclases. Furthermore, activation of MAPK also depends on proteolytic degradation of SCOP (SCN Circadian Oscillatory Protein) by calpain. Interestingly, the persistence of contextual memory is maintained by the circadian oscillation of the cAMP/MAPK/MSK1/CREB transcriptional pathway in area Ca1 of the hippocampus, an oscillation that depends upon CaM-stimulated adenylyl cyclases. The goal of this presentation is to show how all these signaling components act synergistically to produce memory traces in the hippocampus.
Organizer : Yoshitaka Fukada/Kimiko Shimizu
Department of Biophysics and Biochemistry Seminar by Dr. Klein (1, June, 2009)
Theme : Transcriptome Profiling of the Rodent Pineal Gland: The Impact
Dr. David C. Klein
Senior Investigator, Section on Neuroendocrinology, National Institute of Child Health and Human Development, National Institutes of Health, USA
The pineal gland is characterized by a 24-hour activity cycle, which is best represented by the daily rhythm in melatonin production. The rhythm in circulating melatonin provides an indicator of time and is used in a variety of ways to coordinate physiological processes with daily and seasonal changes in environmental lighting. A recently completed study (1) of gene expression in the pineal gland has revealed the highly expressed genes in this tissue and has identified genes which exhibit daily changes in expression, including >600 genes with 2-fold or greater night/day differences. In some cases, the night/day differences are ~100-fold. These changes appear to be due primarily to adrenergic-cyclic AMP signaling. The findings of this effort have triggered investigations of a broad nature, including those related to development, to the molecular nature of pineal/retina similarity, to signal transduction, to the role of the thyroid hormone in pineal signal transduction and to the role of the pineal gland in the immune/inflammatory response. Current work is directed at identifying the conserved genetic features of the vertebrate pineal gland, based on studies of the transcriptomes of the zebrafish, mouse, rhesus and human pineal glands.
Reference:
1) Bailey MJ et al. (2009) Night/day changes in pineal expression of >600 genes: Central role of adrenergic/cAMP signaling. J. Biol. Chem. 284: 7606 -7622.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Brown
Theme : Layers of Clocks: Keeping Cellular Time in Different Frames
Dr. Steven A. Brown
Professor, Institute for Pharmacology and Toxicology, University of Zurich, Switzerland
Human behavior is influenced by many genetic and environmental factors; it is therefore often difficult to study by reductionist approaches. However, in rare cases it can be linked directly to a biological process that can be understood at the cellular level. The circadian clock is one such instance: physiologically, it affects diverse processes such as sleep-wake time, activity patterns, body temperature, cardiac and respiratory rate, renal flow, and digestion. Molecularly, it is present in most cells of the body and modulates the transcription of about ten percent of our genes. Although this clock tells time at a daily level, recent research from my laboratory and others suggests that its mechanism is connected to biological clocks with other metrics. By directly controlling the transcription of some cell cycle genes, the circadian clock likely gates cell division, perhaps in order to segregate DNA replication from catabolic processes. Through shared components, it can be coordinately regulated with cellular senescence pathways. Finally, circadian clock function is itself governed by individual genetic differences and physiology, which explain its different behavior in ageing humans, and thus its subjection to each of our overall "lifetime" clocks. Together, this delicate interplay provides a mechanistic explanation for physiological timing in several frames.
Brown, S.A. et al. (2008) Molecular insights into Human Daily Behavior. Proc. Natl. Acad. Sci. USA, 105:1602-1607.
Brown, S.A. et al. (2005) PERIOD1-associated proteins modulate the negative limb of the mammalian circadian oscillator. Science 308:693-6.
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Albrecht (13, November, 2008)
Theme : Clocks, brain function and dysfunction
Dr. Urs Albrecht
Dept. of Medicine, Div. of Biochemistry University of Fribourg, Switzerland
It is estimated that about 20% of the population in industrialized countries are affected by mood disorders such as depression and eating disorders. One of the hallmarks of industrialized countries is the fact that the natural day/night regime is largely ignored due to the availability of artificial light sources. As a consequence activity well beyond the borders given by nature have become possible. Therefore synchronization of the circadian system by natural cues has become inefficient leading to a misalignement of periodic physiological processes, which can hamper normal brain function. This derailment of the circadian system is probably one of the reasons for the increased incidence of depression, excessive alcohol consumption and over-eating in modern society. Apart from its function in the clock mechanism in the suprachiasmatic nuclei, the clock gene Per2 appears to have additional functions in other areas of the brain. It is postulated that a food entrainable oscillator (FEO) resides in the brain, which is responsible for anticipatory activity in expectation of regularly scheduled meals. A mutation in Per2 leads to loss of food anticipatory activity in mice suggesting an important role of Per2 in the FEO. Interestingly, several studies have found that feeding behavior shares neurobiological mechanisms with the addictive properties of drugs of abuse. Because Per2 not only affects food anticipatory behavior but also modulates the effects of drugs of abuse we postulate that this gene and its protein influences the neurobiological circuitry that is common to feeding signals and drugs, both of which affect the reward system. Evidence will be presented highlighting a role of Per2 in alcohol consumption and cocaine addiction indicating an influence of the clock on glutamatergic as well as dopaminergic signaling. These findings provide a base for development of new approaches in medical treatment of neuropsychiatric disorders.
Spangel, R. et al. (2005) The clock gene Per2 influences the glutamatergic system and modulates alcohol consumption. Nat. Med. 11, 35-42
Hampp, G. et al. (2008) Regulation of Monoamine oxidase A by circadian-clock components implies clock influence on mood. Curr. Biol. 18, 678-683
Organizer : Yoshitaka Fukada
Department of Biophysics and Biochemistry Seminar by Dr. Hardin (15, July, 2008)
Theme : Regulation of transcriptional feedback within the Drosophila circadian clock
Dr. Paul E. Hardin
Department of Biology and Center for Research on Biological Clocks, Texas A&M University, USA
Transcriptional activation by CLOCK-CYC (CLK-CYC) heterodimers and feedback repression by PERIOD-TIMELESS (PER-TIM) heterodimers are essential for circadian oscillator function in Drosophila. The function of these transcriptional regulators is regulated by post-translational modifications that alter DNA binding, stability and chromatin modifications. We find that binding of CLK-CYC heterodimers containing hypophosphorylated CLK to E-box elements promotes chromatin modifications that enhance transcriptional activation of per, tim and other circadian oscillator components. PER protein then begins to accumulate, but in a delayed fashion due to DOUBLE-TIME (DBT) dependent phosphorylation and subsequent stabilization by TIM binding. PER-TIM-DBT complexes then enter the nucleus and bind to CLK-CYC, thus promoting the hyperphosphorylation of CLK, loss of CLK-CYC E-box binding, and transcriptional repression. Recent experiments using the PERδ mutant, which is unable to bind DBT, and hypomorphic dbtar and dominant negative dbtK/R mutants suggest that DBT acts as a bridge to recruit other kinase(s) into PER-TIM-DBT-CLK-CYC complexes. Once these kinases enter DBT-PER-CLK complexes they phosphorylate PER and CLK, thereby promoting transcriptional repression. Subsequent phosphorylation of PER and CLK by DBT promotes PER and CLK degradation, thereby relieving transcriptional repression.
References:
Yu, W., H. Zheng, J. H. Houl and P. E. Hardin (2006) PER dependent rhythms in CLK phosphorylation and E-box binding regulate circadian transcription. Genes Dev. 20, 723-733.
Kim, E. Y., H. W, Ko, W. Yu, P. E. Hardin and I. Edery (2007) A DOUBLETIME kinase binding domain on the Drosophila PERIOD protein is essential for its hyperphosphorylation, transcriptional repression and circadian clock function. Mol. Cell. Biol. 27, 5014-5028.
Organizer : Yoshitaka Fukada