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Dana M. García, Ph. D. Professor of Biology Phone: 512-245-3368 Fax: 512-245-8713 Email: dana_garcia@txstate.edu Office Hours: TBA
Department of Biology
Texas State University-San Marcos 601 University Drive San Marcos, TX 78666 |
Our National Science Foundation-funded research is directed toward understanding how the neural retina of fishes lets the retinal pigment epithelium know when it's light or dark outside. The retinal pigment epithelium, or RPE, is a tissue made up of a single layer of cells that reside between the rod and cone photoreceptors of the retina and the choroid, which carries the capillaries that supply the retina with nutrients. The RPE cells themselves are shaped sort of like squid with long tentacles and are chock full of melanin-pigment granules. The tentacles reach down among the outer segments of the photoreceptors, which is where light reception and visual processing begins. When it's light out, the melanin pigment granules migrate out of the cell body into the tentacles, or apical processes. This migration, which is typically referred to as pigment dispersion, helps shield the rod photoreceptors from excessive light and photobleaching. When it's dark out, the pigment granules migrate back into the cell body, and this pigment aggregation unmasks the rod photoreceptors so that they can maximize light capture.
The RPE don't seem to respond to light directly, and several lines of evidence suggest that the retina secretes signals that the RPE responds to by moving its pigment granules. We have evidence that one of these signals is the classical neurotransmitter acetylcholine, to which the RPE responds by dispersing pigment granules. In other words, acetylcholine induces light adaptive responses in RPE isolated from fish eyes.
In order for a chemical messenger like acetylcholine to interact with a cell and influence that cell's activity, it must bind to a receptor located at the cell surface. This receptor functions in transmitting a message to the cell's interior that the neurotransmitter is present, and starting the cascade of events that leads to the cell's response to that messenger. Our research effort is directed toward discovering the nature of the receptor acetylcholine binds on the surface of the RPE and activates to stimulate pigment granule dispersion. Work done by many other scientists has shown that acetylcholine acts through two major types of receptors in other systems. The first subtype is the nicotinic receptor, an example of which is found at the neuromuscular junction, or the site where communication between the nervous system and individual skeletal muscle cells takes place. The second type of acetylcholine receptor is the muscarinic receptor, but in humans this type actually includes a minimum of five subtypes, m1-m5. It's not known how many subtypes fish have, but sequences for two muscarinic receptor genes have been published for zebrafish and have been designated as m2 and m5.
We are currently using a pharmacological approach to uncover the receptor subtype activated by acetylcholine (or its analog carbachol), and a molecular approach to discover the sequence(s) of gene(s) encoding muscarinic receptors in bluegill. Our pharmacological studies have hinted that activation of an m1, m3 or m5 receptor (or some combination) stimulates pigment granule dispersion. Studies are currently underway to determine which of these receptors is expressed by the retinal pigment epithelium of bluegill.
Biology 3421 Vertebrate Physiology (link to syllabus and notes)
Biology 4300 Neurobiology (link to pdf syllabus and index of notes)
Biology 5300 Neurobiology (see 4300)
Cell Signaling
Phatarpekar, P. V., S. F. Durdan, C. M. Copeland, E. L. Crittenden, J. D. Neece and D. M. García. 2005. Molecular and Pharmacological characterization of muscarinic receptors in retinal pigment epithelium: role in light-adaptive pigment movements. J. Neurochem. 95:1504-1520. [pdf; This is an electronic version of an article published in Journal of Neurochemistry: complete citation information for the final version of the paper, as published in the print edition of Journal of Neurochemistry, is available on the Blackwell Synergy online delivery service, accessible via the journal's website at http://www.blackwellpublishing.com/jnc or http://www.blackwell-synergy.com]
García, D. M. 1998. Carbachol-induced pigment granule dispersion in teleost RPE. Cytobios 94 : 31-37.
García, D. M. and B. Burnside. 1994. Suppression of cAMP induced pigment granule aggregation by inhibitors of organic anion transport. Invest. Ophthalmol. Vis. Sci. 35 : 178-188.
Cytoskeleton
García, D. M., S. E. Weigum and J. R. Koke. 2003. GFAP and nuclear lamins share an epitope recognized by monoclonal antibody J1-31. Brain Research 976(1):9-21.
Dixson, J. D., M. R. J. Forstner and D. M. García. 2003. Evolutionary history of the alpha-actinin gene family: a phylogenetic study. J. Mol. Evol. 56(1):1-10.
Glass, T. L., T. R. Raabe, D. M. García and J. R. Koke. 2002. Phosphorylated neurofilaments and SNAP-25 in SH-SY5Y neuroblastoma cells in vitro. Brain Res. 934(1):34-48.
Bolanos, S. H., D. O. Zamora, D. M. García, and J. R. Koke. 1998. An alpha-actinin isoform that may cross-link intermediate filaments and microfilaments. Cytobios 94 : 39-61.
García, D. M. and J. R. Koke. 1996. The cytoskeleton of the retinal pigment epithelium. In: S. K. Malhotra, ed. Advances in Structural Biology , vol. 4, Greenwich, Connecticut: JAI Press, Inc., pp. 151-174.
Science Education
Westerlund, J. F., D. M. García, J. R. Koke, T. A. Taylor and D. S. Mason. 2002. Summer scientific research for teachers: the experience and its effect. J. Science Teacher Education 13(1):63-83.
Katherine Saul (8/08, exp; co-Chair w/Dr. Koke) Differential Gene Expression in Danio rerio During Optic Nerve Regeneration. Currently pursuing Ph.D. at Texas State Univesity.
Elizabeth Crittenden (5/08) Modd Muscarinic Receptor Expression in Bluegill Retinal Pigment Epithelium. Currently training in cytogenetics at Mayo Clinic.
Adam Johnson (8/07) Ca2+ Requirements and Beyond: Signal Transduction in Pigment Granule Motility of Retinal Pigment Epithelium. Currently in medical school at UTMSC-Houston..
Varsha Radhakrishnan (5/07) Molecular Characterization and Expression of Gq/11 Protein in Fishes. Currently technician at UTHSCSA.
Richard Nuckels (12/06) Ontogeny of Muscarinic Acetylcholine Receptor Expression in the Eyes of Zebrafish. Currently employed as a research associate at UT.
Chad Copeland (5/05) Muscarinic Receptor Subtypes Involved in Pigment Granule Dispersion in Retinal Pigment Epithelium. Currently employed in environmental science.
Prasad Phatarpekar (8/04) Isolation and Sequencing of Muscarinic Receptor Genes from Fishes. Currently Ph. D. student in the Graduate School for Biomedical Sciences, UT Houston.
Jamie D. Dixson (12/01) Evolution of the Alpha-Actinin Gene Family. Currently businessman in Dallas area.
Jack N. Needham, Jr. (8/01) Molecular Characterization of Alpha-Actinin. Currently medical intern in Brooklyn, NY.
Alfredo González, III (12/00) Muscarinic Regulation of Pigment Granule Dispersion in Teleost Retinal Pigment Epithelium. Currently businessman in Laredo, TX.
Corey Waller (5/99) Synthesis of Polyhedral Boranes for Use in Boron Neutron Capture Therapy for Cancer. Currently M.D.
Ernesto Pérez, Jr. (5/99) Characterization of the Intermediate Filament Cytoskeleton in Teleost Retinal Pigment Epithelium. Has Ph. D. from UTSA and is currently teaching at a community college in San Antonio.
David Zamora (8/97) Localization of Cytoskeletal Elements in Teleost Retinal Pigment Epithelium. Currently at University of Texas Health Sciences Center in San Antonio as a post-doctoral associate.
Shobhit Sharma (5/09, exp) Regulation of pigment granule movement in bluegill RPE
Elizabeth Capalbo (8/09, exp) Muscarinic receptors in zebrafish.
James Neece (12/08, exp) Heterologous expression of fish muscarinic receptors in CHO cells.
Visiting Ph. D. Student
Jesse Muñoz. Microarray analysis of gene expression as a function of diurnal cycle in zebrafish. Currently post-doctoral research associate at UT Health Science Center-San Antonio.
Past Post-doctoral Research Associate
Simon Durdan, Ph. D. Analysis of the Expression of Muscarinic Receptors in Bluegill Tissues using RT-PCR. Currently continuing post-doctoral studies at UCSF in Juan Korenbrot's lab.
Curriculum Vitae
Available in Portable Document Format. (.pdf) Download
A truncated version is available online.
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