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Samer Hattar, Ph.D.
Assistant Professor
Department of Biology
Joint Appointment
Department of Neuroscience (JHMI)
Undergraduate
Yarmouk University, Jordan
1988-1991
Masters
American University of Beirut, Lebanon
1991-1993
Graduate
University of Houston, U.S.A.
1993-2000
Postdoctoral Fellow
Johns Hopkins University-School of Medicine, Howard Hughes Medical Institute, U.S.A.
2000-2004 |
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Department of Biology
Johns Hopkins University
3400 N. Charles Street
Baltimore, MD 21218-2685
U.S.A. |
Office Telephone:
Lab
Telephone:
Department Fax:
Email: |
410.516.4231
410-516-7641
410.516.5213
shattar@jhu.edu |
Office- Mudd Hall 227
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[Research Interests] [Representative Publications]
RESEARCH INTERESTS
Vision beyond image formation: The role of melanopsin cells in regulating mammalian physiology
Our ability to observe and enjoy the beauty of a spring blossom or the fascinating fall colors is critically dependent on the ability of our retina to capture photons and then signal this information all the way to the visual cortex. Image formation uses the classical photoreceptor cells, known as rods and cones. Rods and cones contain photopigments (light-absorbing pigments), which are composed of a protein moiety (opsin, which is a G-protein coupled receptor) and a vitamin-A-based chromophore (11-cis-retinal). Rhodopsin and cone opsins capture the light energy (photons) and transduce it into an electrical signal, which is the currency understood by neurons. Interestingly, in humans, light impacts many physiological functions including sleep and mood that are important for quality of life. Our interest pertains to understanding the cellular, molecular and behavioral pathways by which light influences several light-dependent physiological functions independent of image formation. These light-dependent functions include adjusting our internal biological clock to the outside solar day, constricting our pupils to control the amount of light passing through to the retina and the direct light alerting signals.
For many years, it was assumed that rods and cones are the only photoreceptors capable of detecting light in the mammalian retina. However, research from several laboratories uncovered a third type of photoreceptor cell in the mammalian retina. These cells express the photopigment melanopsin first identified by Ignacio Provencio and colleagues, and were shown to be intrinsically photosensitive by David Berson and colleagues. Robert Lucas and colleagues were the first to show conclusively (yet indirectly) that the melanopsin cells absorb light maximally at different wavelength than those of rods and cones. We in close, fruitful and continuing collaborations with Robert Lucas and David Berson have shown that these cells target specifically non-image-forming centers in the brain including the suprachiasmatic nucleus (center for the circadian pacemaker), and the olivary pretectal nucleus (the area responsible for pupil constriction) among many others. The main purpose of our research is to understand both the mode of action of these newly identified photoreceptors, and the individual contributions of the rods, cones and these novel photoreceptors in signaling light for non-image-forming visual functions. Recently, we genetically engineered mice where the Diphtheria toxin (aDTA) is specifically expressed in melanopsin-containing retinal ganglion cells. We showed that the Opn4aDTA animal have normal image functions but lack the ability for circadian photoentrainment. These studies are interesting because they indicate that the ability to form images does not allow animals to detect light for a seemingly simple function such as ajusting the circadian clock to the outside solar day. A wonderful review by Russ Van Gelder in Nature Neuroscience describes the implications of this study (Van Gelder RN. How the clock sees the light. Nat Neurosci. 2008 Jun;11(6):628-30.)
REPRESENTATIVE PUBLICATIONS
Altimus, C.M., LeGates, T.A., Hattar, S., 2009. Circadian and Light effects on Mood Regulation. Chapter in Mouse Models of Mood and Anxiety disorders, NeuroMethods. 42: 47-65. Humana Press, New York, NY.
Badea, T.C., Cahill, H., Ecker, J., Hattar, S., Nathans, J., 2009. Distinct roles of transcription factors brn3a and brn3b in controlling the development, morphology, and function of retinal ganglion cells. Neuron, 61, 852-64.
Altimus, C.M., Güler, A.D., Villa, K.L., McNeill, D.S., Legates, T.A., Hattar, S., 2008. Rods-cones and melanopsin detect light and dark to modulate sleep independent of image formation. PNAS, 105, 19998- 20003.
Güler, A.D., Ecker, J.L., Lall, G.S., Haq, S., Altimus, C.M., Liao, H.-W., Barnard, A.R., Cahill, H., Badea, T.C., Zhao, H., Hankins, M.W., Berson, D.M., Lucas, R.J., Yau, K.-W., Hattar, S., 2008. Melanopsin cells are the principal conduits for rod–cone input to non-image-forming vision. Nature, 453, 102-5.
Hattar, S., Kumar, M., Park, A., Tong, P., Tung, J., Yau, K.-W., Berson, D.M.2006. Central projections of melanopsin-expressing retinal ganglion cells in the mouse. J Comp Neurol. 497:326-49.
Barnard, A.R., Hattar, S., Hankins, M.W., Lucas, R.J. 2006. Melanopsin regulates visual processing in the mouse retina. Curr Biol 16:389-95.
Mrosovsky, N., Hattar, S. 2005. Diurnal Mice (Mus Musculus) and Other Examples of Temporal Niche Switching. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 191: 1011-24.
Sekaran, S., Lupi, D., Jones, S.L., Sheely, C.J., Hattar, S., Yau, K.-W., Lucas, R.J., Foster, R.G., and Hankins, M.W. 2005. Melanopsin-Dependent Photoreception Provides Earliest Light Detection in the Mammalian Retina. Curr Biol. Published online.
Hattar, S., Lucas, R.J. Mrosovsky, N., Thompson, S., Douglas, R.H., Hankins, M.W., Lem, J., Biel, M., Hofmann, F., Foster, R.G., and Yau, K.-W., 2003. Melanopsin and Rod–Cone Photoreceptive Systems Account for All Major Accessory Visual Functions in Mice. Nature 424, 76-81.
Lucas, R.J., Hattar, S., Takoa, M., Berson, D.M., Foster, R.G., and Yau K.-W. 2003. Diminished Pupillary Light Reflex at High Irradiances in Melanopsin-Knockout Mice, Science 299:245–247.
Hattar, S., Liao, H.-W., Takoa, M., Berson, D.M., and Yau, K.-W. 2002. Melanopsin-Containing Retinal Ganglion Cells: Architecture, Projections, and Intrinsic Photosensitivity. Science 295, 1065-70.
Hattar, S., Lyons, L.C., Dryer, L., and Eskin, A. 2002. Circadian Regulation of the Transcription Factor, ApC/EBP in the Eye of Aplysia Californica. J Neurochem 83:1401-11.
Zwartjes, R.E., West, H., Hattar, S., Ren, X., Noel, F., Nuñez-Regueiro, M., MacPhee, K., Homayouni, R., Crow, M.T., Byrne, J.H., and Eskin, A. 1998. Identification of Specific mRNAs Affected by Treatments Producing Long-Term Facilitation in Aplysia. Learning & Memory 4:478-495.
Liu, Q.R., Hattar, S., Endo, S., MacPhee, K., Zhang, H., Cleary, L.J., Byrne, J.H., and Eskin, A. 1997. A Developmental Gene (Tolloid/BMP-1) is Regulated in Aplysia Neurons by Treatments that Induce Long-Term Sensitization. J Neurosci. 17, 755-764.
Lab Members
Graduate Students:
Cara Altimus
Vanessa Matos-Cruz
David McNeill
Catherine Sheely
Tara LeGates
Kylie Chew
Lin Bao
Postdoctoral Fellows:
Alen Chen
Research Specialist:
Sahar Rahiem
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