Dr. Clark joined the Department of Microbiology and Immunology as an
Assistant Professor in 1996 and was promoted to Associate Professor
in 2003. He is currently Director of Graduate Studies in the Graduate
Field of Immunology and a member of the Aquatic Animal Health Program
within the department. He received his BS from Columbia University in
Bioengineering, and his PhD from the State University of New York at
Stony Brook in Cell and Developmental biology. His research is supported
by the NIH, NSF and USDA, and is directed towards a number of projects
dealing with vaccine development, host-pathogen interactions, and the
evolution of adaptive immunity.
Research Interests
| Graduate Fields | Lab
Members | Related Links | Selected
References
Research Interests
Research in the Clark laboratory is focused in three mains areas. We
have a long-standing interest in mechanisms of immune evasion and have
worked extensively with Ichthyophthirius multifiliis, a parasitic protozoan
of fish, as a model system. More recently, we have begun to develop
the free-living pond-water ciliate, Tetrahymena thermophila, as a high-level
protein expression system for vaccine antigens. Lastly, we are interested
in the evolution of adaptive immunity and have turned to transgenic
zebrafish models to examine sites of antigen-presentation in teleosts.
1. Mechanisms of immune evasion
As the causative agent of "white spot", I. multifiliis
has substantial impact on commercial aquaculture worldwide. At the same
time, it provides an extremely useful model for studies of host-parasite
interactions, and the development of cutaneous immunity in lower vertebrates.
A number of years ago, we showed that immunity against Ichthyophthirius
involves a novel effect of antibody on parasite behavior. Rather than
being killed, parasites are forced to exit fish prematurely in response
to antibody binding. The target antigens in this case are abundant GPI-anchored
proteins on the parasite surface known as i-antigens. The fact that
premature exit requires antigen cross-linking (rather than antibody
binding per se) has suggested a role for GPI-anchored proteins and lipid
rafts in transmembrane signaling in I. multifiliis. Recently, we have
found that lateral clustering of i-antigens at the parasite surface
triggers a dramatic alteration of the lipid raft proteome, along with
changes in serine/threonine and tyrosine phosphorylation of raft-associated
proteins in ciliary and plasma membranes. These results clearly suggest
that GPI-anchored proteins can transduce signals in protozoa and that
raft mediated signaling evolved well before the emergence of metazoa.
In connection with the parasite studies, a high-throughput sequencing
project is currently underway to determine 36,000+ cDNA sequences from
I.multifiliis at different stages of the parasite life cycle.
2. Tetrahymena as a high-level expression system for vaccine antigens.
On a more practical level, the laboratory has devoted considerable effort
to the development of Tetrahymena thermophila, a free-living pond-water
ciliate, as a novel platform for large-scale expression of eucaryotic
membrane proteins. This includes candidate vaccine antigens from a number
of parasitic protozoa (most notably Ichthyophthirius, and the human
pathogen, Plasmodium falciparum), as well as drug targets for clinically
important diseases of humans and animals. As part of these efforts,
the Clark laboratory maintains an NIH-funded stock center for T. thermophila
strains, and is involved in on-going efforts to physically map the Tetrahymena
genome.
3. Evolution of antigen presentation.
As the earliest extant organisms in which adaptive immunity appeared,
fish offer unique opportunities for studying the evolution of the acquired
immune system. Despite this, almost nothing is known about antigen presentation
in fish, and professional antigen-presenting cells have yet to be identified
in teleosts. Comparative analyses reveal the presence of many homologs
of mammalian DC markers in trout, catfish, fugu and zebrafish genomes.
The laboratory is in the process of generating transgenic zebrafish
that contain reporter genes driven by DC-specific promoters with the
long-term goal of identifying and characterizing teleost DCs in vivo
and in vitro, and determining their role in antigen presentation in
fish.
Graduate Fields
Dr. Clark is a member of the following Graduate Fields:
Comparative Biomedical Sciences
Immunology
Lab Members
Yelena Bisharyan, Technical Support and Graduate Student
Donna Cassidy-Hanley, Senior Research Associate
Mossamal Hossain, Technical Support
Related Links
Aquatic Animal Health Program
"The Ich Page" at the University of Gerogia
Selected References
Lin, Y., Cheng, G., Wang, X., and T. G. Clark (2002). The use of
synthetic genes for the expressions of ciliate proteins in heterologous
systems. Gene.
288:85-94.
Lin, Y., Lin, T. L., Wang, C. C., Wang, X., Klobfleisch, R., Stieger,
K., and T. G. Clark (2002). Variation in primary sequence and tandem
repeat copy number among i-antigens of Ichthyophthirius multifiliis.
Mol.
Biochem. Parasitol. 120:93-106.
Orth, R. N., Kameoka, J., Zipfel, W. R., Ilic, B., Webb, W. W., Clark,
T. G. and H. G. Craighead (2003). Creating biological membranes on the
micron Scale: Forming patterned lipid bilayers using a polymer lift-off
technique. Biophys.
J. 85:3066-3073.
Bisharyan, Y., Chen, Q., Hossain, M. M., Papoyan, A., and T. G. Clark
(2003). Cadmium effects on Ichthyophthirius: evidence for metal-sequestration
in fish tissues following administration of recombinant vaccines. Parasitology
126:Suppl:S87-93.
Clark, T.G. and D. Cassidy-Hanley (2004). Recombinant subunit vaccines:
Potential and constraints. Dev.
Biol. Stand. 121:153-163.
Clark, T.G. (2005). Molecular approaches and techniques. In: Fish Diseases
and Disorders, Volume 1: Protozoan and Metazon Infections. (ed. P.T.K.
Woo, CABI Publishing, Oxon, U.K.).
