Dana M. García, Ph. D.
Professor of Biology
Department of Biology
Texas State University-San Marcos
601 University Drive
San Marcos, TX 78666
Research in the García lab has historically been oriented toward understanding the mechanisms through which light- and dark-adaptation are accomplished in the retina of fishes. Of particular interest are those processes involved in regulating pigment granule movements in the retinal pigment epithelium (RPE). As reflected in the publications and theses listed below, much of our effort has been oriented toward discovering how acetylcholine activates light-adaptive pigment granule dispersion in retinal pigment epithelium, both in terms of the cell surface receptors involved and the downstream signaling processes.
Our research using RPE isolated from green sunfish and bluegill supports a model in which acetylcholine activates a muscarinic receptor, activating a G-protein, which in turn activates phospholipase C, leading to release of calcium from intracellular stores and consequent pigment granule dispersion. Furthermore, using immunohistochemistry we have demonstrated that bluegill RPE express m3 and m5 muscarinic receptors, consistent with our pharmacological results. It remains to be determined whether acetylcholine is a physiologically relevant signal for light adaptive responses in the fish. Our work in zebrafish suggests that muscarinic receptors (m1a, m1b, m3a, m3b, m5a and m5b) are expressed in the eye early in development. Based on others' work reporting that rudimentary light- and dark-adaptive movements are initiated by 5 days, but not fully developed until adulthood, our work indicates that muscarinic receptors may be present by the time pigment granule movements are initiated. Interestingly, muscarinic receptors (m2 and m5) show diurnal changes in their expression levels at the mRNA level while m3 receptors show changes at the protein level.
We are also interested in dark-adaptive processes, specifically exploring the hypothesis that photoreceptors export cyclic nucleotides in the dark using an ATP-binding cassette transporter, and those cyclic nucleotides, acting as both a first and second messenger, are taken up by the RPE and elicit dark-adaptive pigment granule aggregation. Evidence in support of this model comes from studies on green sunfish and bluegill RPE showing that treating isolated RPE with non-derivatized cAMP induces pigment granule aggregation and that aggregation is inhibited by treating cells with inhibitors of organic anion transport. The same treatment blocks uptake of tritiated cAMP, providing direct evidence of transport-mediated uptake of cAMP. Currently, we are probing zebrafish retina to determine the presence and location of MRP4.
Zebrafish express duplicate forms of many of the genes involved in pigmentation and we are currently working to understand both the regulation of duplicate genes as well as the role of their gene products in influencing pigment granule position in both melanophores (pigmented cells of the skin) and RPE. Interestingly, suprisingly few genes are show a diurnal rhythm in their expression in the eye.
Publications (by topic)
Optic Nerve Regeneration
Neve, L. D., A. A. Savage, J. R. Koke and D. M. García. 2012. Activating transcription factor 3 and reactive astrocytes following optic nerve injury in zebrafish. Comparative Biochemistry and Physiology, part C, 155(2):213-218. (doi: 10.1016/j.cbpc.2011.08.006 ).
Saul, K. E., J. R. Koke and D. M. García. 2010. Activating transcription factor 3 (ATF3) expression in the neural retina and optic nerve of zebrafish during optic nerve regeneration. Comparative Biochemistry and Physiology, part A 155:172-182. (doi: 10.1016/j.cbpa.2009.10.042 ).
Nuckels, R. J., M. R. J. Forstner, E. L. Capalbo-Pitts and D. M. García. 2011. Developmental expression of muscarinic receptors in the eyes of zebrafish. Brain Research 1405:85-94.
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.blackwell-synergy.com
González, A. III, E. L. Crittenden and D. M. García. 2004. Activation of muscarinic acetylcholine receptors elicits pigment granule dispersion in retinal pigment epithelium isolated from bluegill. BMC Neuroscience 5:23.
García, D. M. 1998. Carbachol-induced pigment granule dispersion in teleost RPE. Cytobios 94 : 31-37.
King-Smith, C., P. Chen, D. M. García, H. Rey and B. Burnside. 1996. Calcium-independent regulation of pigment granule aggregation and dispersion in teleost retinal pigment epithelial cells. J. Cell Sci. 109 : 33-43.
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.
Koke, J. R., A. L. Mosier and D. M. García. 2010. Intermediate filaments of zebrafish retinal and optic nerve astrocytes and Müller glia: Differential distribution of cytokeratin and GFAP. BMC Research Notes:3:50.
García, D. M., H. Bauer, T. Dietz, T. Schubert, J. Markl and M. Schaffeld. 2005. Identification of keratins and analysis of their expression in carp and goldfish: comparison to the zebrafish and trout keratin catalog. J. Cell and Tissue Research 322:245-256.
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.[pdf]
Weigum, S. E., D. M. García, T. R. Raabe, N. Christodoulides and J. R. Koke. 2003. Discrete nuclear structures in actively growing neuroblastoma cells are revealed by antibodies raised against phosphorylated neurofilament proteins. BMC Neuroscience 4:6.
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.
Schwartz, R., J. Westerlund, D. García and T. Taylor. 2010. The impact of full immersion scientific research experiences on teachers’ views of the nature of science. Electronic Journal of Science Education 14:2.
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.
Aptamer-based Therapeutic Strategies
Ruben Tovar (5/14) Ocular Histology in Three South Central Texas Paedomorphic Salamander Species (Eurycea sosorum, Eurycea nana and Eurycea rathbuni) and Comparative Ocular Development of Two Morphotypes. Currently Ph.D. student at University of Tulsa in Ron Bonnett’s laboratory.
Kris Freeman (8/13) Proteomic Comparison between MRP4 Knockout and Wild Type Mouse Brain, Liver, Kidney and Serum. Currently Oncology Account Executive for Myriad Genetics.
Carlos Quintanilla (8/12) Expression and Localization of Mrp4 in the Retinal Tissue of Danio rerio. Currently scientist at PPD in Virginia.
Luis Neve (12/11) Identification and Characterization of Reactive Astrocytes following Optic Nerve Injury in Zebrafish. Currently medical student.
Shobhit Sharma (5/11) Diurnal Variation in Melatonin Receptor Expression in Zebrafish Eyes. Currently Ph.D. student in Aquatic Resources program at Texas State University-San Marcos.
Elizabeth Capalbo (12/09) Diurnal Expression of Muscarinic and Dopaminergic Receptors in the Eye of Zebrafish. Currently teaching high school in Houston area.
Katherine Saul (8/08; co-Chair w/Dr. Koke) Differential Gene Expression in Danio rerio During Optic Nerve Regeneration. Currently research assistant at the University of Colorado at Denver.
Elizabeth Crittenden (5/08) Modd Muscarinic Receptor Expression in Bluegill Retinal Pigment Epithelium. Currently cytogeneticist in Spokane, Washington.
Adam Johnson (8/07) Ca2+ Requirements and Beyond: Signal Transduction in Pigment Granule Motility of Retinal Pigment Epithelium. Currently medical resident at Vanderbilt University.
Varsha Radhakrishnan (5/07) Molecular Characterization and Expression of Gq/11 Protein in Fishes. Currently residing in Houston.
Richard Nuckels (12/06) Ontogeny of Muscarinic Acetylcholine Receptor Expression in the Eyes of Zebrafish. Currently Ph.D. student in Aquatic Resources program at Texas State University-San Marcos. (see below).
Chad Copeland (5/05) Muscarinic Receptor Subtypes Involved in Pigment Granule Dispersion in Retinal Pigment Epithelium. Currently managing Storm Water Pollution Prevention division at Ranger Environmental.
Prasad Phatarpekar (8/04) Isolation and Sequencing of Muscarinic Receptor Genes from Fishes. Ph. D. from 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 Board-certified surgeon in west Texas.
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 emergency room physician in Michigan.
Ernesto Pérez, Jr. (5/99) Characterization of the Intermediate Filament Cytoskeleton in Teleost Retinal Pigment Epithelium. Currently post-doc at University of Massachusetts Medical School.
David Zamora (8/97) Localization of Cytoskeletal Elements in Teleost Retinal Pigment Epithelium. Currently principal investigator at Brooks Army Medical Center in San Antonio.
Former Visiting Ph. D. Student
Jesse Muñoz. Microarray analysis of gene expression as a function of diurnal cycle in zebrafish. Currently instructor at South Texas College in McAllen, Texas.
Past Post-doctoral Research Associate
Simon Durdan, Ph. D. Analysis of the Expression of Muscarinic Receptors in Bluegill Tissues using RT-PCR. Currently scientist in UK.