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Graham H. Thomas Assistant Professor of Biology and of Biochemistry and Molecular Biology   Ph.D. University of Edinburgh, UK. Postdoctoral Appointments Washington University in St. Louis Harvard University

• Telephone: (814) 863-0716
• Email: (GXT5@PSU.EDU)

Photographs of Scotland - the P.I.'s homeland. 

Research Interests

Research in my lab asks fundamental questions about the roles of the cytoskeleton at the cell membrane in epithelial cells, including issues of cell polarity and adhesion, cell signaling, and morphogenesis. Drosophila is our model system because of the multidisciplinary combination of tools available, and because of its well characterized development. We use both molecular and cellular techniques as well as classical and transgenic genetic approaches.

The spectrin-based membrane skeleton is a ubiquitous structure that is conserved in diverse organisms. Spectrins are long heterotetramers of two a and two b chains, which crosslink F-actin and contain numerous protein binding sites along their length. Typically different spectrins are polarized to distinct parts of the plasma membrane. Drosophila provides a simple model system for examining this molecular scaffold, since the fly has only one a and two b-genes: the type of spectrin thus depends on which b chain is used. Our goal is to understand how differentiation in the membrane skeleton is used to polarize cells in a developmental context.

We are currently focusing on one of these b-spectrin isoforms, b[Heavy]-spectrin (bH), which is associated with the zonula adherens, apical microvillar fields and morphogenetic movements driven by cytoplasmic myosin II. The distribution of bH during early embryogenesis suggests a role in early events that result in cell polarization, and mutations in the locus encoding this protein cause a number of defects in tissues of epithelial origin, including failure of at least one polarized signaling pathway that leads to a specific cell fate defect.

Our most recent phenotypic analysis of the karst mutation and careful immunofluorescent studies on the behavior of both b-spectrins during primary epithelium formation has revealed two significant results. First, apical and basolateral spectrin behave in quite distinct ways that suggest different rather than truly analogous roles in their respective domains as many have assumed. Second, apical spectrin is necessary for normal apical contraction (a classic cell shape change that is required for generating form in epithelia) and for maintaining the integrity of the zonula adherens. Suprisingly, bH function is not closely associated with the apicobasal polarization pathway: karst mutants can generate and maintain epithelia with bona fide apicobasal polarity. We are thus beginning to redefine and clarify some of the long-established notions concerning the roles of the spectrin-based membrane skeleton in epithelia.

We also maintain and interest in the evolutionary origins of the membrane skeleton through collaboration with Dr. Andrew Clark (Penn State) and Dr. Spencer Muse (North Carolina State University). This collaboration has generated a comprehensive model for the evolution of the a-actinin/spectrin/dystrophin superfamily of proteins. We have found evidence that the ancestral gene structures of this superfamily were unstable during an early phase in their evolution and that this phase was dominated by concerted evolution. This has been followed by long-term stability in gene organization and a lack of sequence exchange between them. This model has general applicability for other proteins with repetitive structures. We are also attempting to identify novel functionality in known spectrin proteins through the analysis of regional differences in evolutionary rate within these proteins. Eventually such analyses may provide new directions for our molecular analyses, as well as some insight into the origins of morphogenetic processes involving these proteins.

My laboratory provides training in a variety of techniques that have wide applicability to other experimental systems. Furthermore, our multidisciplinary approach means that a typical experiment might include several of these. Experiments currently in progress use standard molecular biological techniques (such as PCR, cloning, sequencing and bacterial protein expression), the generation of a transgenic flies expressing mutant proteins, immunofluorescent microscopy with digital image acquisition and the analysis of genetic interactions.

Funding in my lab comes from the National Institutes of Health.

Fly Publications

Papers:

1. Zarnescu, D.C. and Thomas, G.H. 1999. Apical spectrin is essential for epithelial morphogenesis but not apicobasal polarity in Drosophila. J. Cell Biol. 146;1075-1086
2. Thomas G.H. and Williams, J.A. 1999. Dynamic rearrangement of the spectrin membrane skeleton during the generation of epithelial polarity in Drosophila. J. Cell Sci. 112; 2483-2852 Also see our cover on this issue.
3. Thomas G.H. 1998. Molecular evolution of spectrin repeats. BioEssays 20;600
4. Thomas G.H., Zarnescu, D.C, Juedes, A.E., Bales, M.A., Londergan, A., Korte, C.C., Kiehart, D.P. 1998. Drosophila b[Heavy]-spectrin is essential for development and contributes to specific cell fates in the eye. Development 125;2125-2134. Also see our cover on this issue.
5. Thomas G.H., Newbern E.C., Korte C.C., Bales M.A., Muse S.V., Clark A.G. and Kiehart D.P. 1997. Intragenic duplication and divergence in the spectrin superfamily of proteins. Mol. Biol. Evol. 14;1285-1295 - (contains the completed bH sequence)
6. Muse S.V., Clark A. G. and Thomas G.H. 1997. Comparison of the nucleotide substitution process among repetitive setgments of the alpha- and beta-spectrin genes. J. Mol. Evol. 44;492-500
7. Thomas G.H. and Kiehart D.P. 1994. Beta-Heavy spectrin has a restricted tissue and subcellular distribution during Drosophila Development. Development 120;2039-2050. Also see our cover on this issue.
8. Glaser R.L. Thomas G.H., Siegfried E., Elgin S.C.R. and Lis J.T. 1990. Optimal heat-induced expression of the Drosophila hsp26 gene requires a promoter sequence containing (CT)n.(GA)n repeats. J. Mol. Biol. 211;751-761
9. Gilmour D.S., Thomas G.H. and Elgin S.C.R. 1989. Nuclear proteins from Drosophila embryos bind to polypurine-polypyrimidine sequences in promoter regions. Science 245;1487-1490
10. Thomas G.H. and Elgin S.C.R. 1988. Protein/DNA architecture of the DNase I hypersensitive region of the Drosophila hsp26 promoter. EMBO J. 7;2191-2201
11. Siegfried E., Thomas G.H., Bond U.M. and Elgin S.C.R. 1986. Characterization of a supercoil-dependent S1 sensitive site 5' to the Drosophila melanogaster hsp26 gene. Nucleic Acids Res. 14;9425-9444

Methods:

1. Kiehart D. P., Montague R., Rickoll W., Foard D. and Thomas G. H. 1994. High resolution microscopic methods for the analysis of cellular movements in Drosophila embryos. Meth. in Cell Biol. 44;507-532
2. Hull M.W., Thomas G.H., Huibregtse J.M. and Engelke D.R. 1991. Protein-DNA interactions in vivo - Examining genes in Saccharomycese cerevisiae and Drosophila melanogaster by chromatin footprinting. Meth. in Cell Biol. 35;383-415
3. Thomas G.H. and Elgin S.C.R. 1988. The use of the alpha-amanitin-resistant subunit of RNA polymerase II as a selectable marker in cell transformation. Drosophila Information Service 67;84

Reviews and Symposia Volumes:

1. Dietz, T.J., Cartwright, I.L., Gilmour, D.S., Siegfried, E., Thomas, G.H., Elgin, S.C.R. 1989. The chromatin structure of hsp26. pp.15-24 in 'Stress-induced Proteins' ed. Pardue, M.L., Feramisco, J., Lindquist, S. (A.R. Liss, New York, NY)
2. Elgin, S.C.R., Cartwright, I.L., Fleischmann, G., Gilmour, D.S., Thomas, G.H. 1989. Alterations in chromatin structure associated with gene activation. pp. 287-296 in 'DNA-Protein Interactions in Transcription', ed. Gralla, J. (A.R. Liss, New York, NY)
3. Elgin, S.C.R., Cartwright, I.L., Gilmour, D.S., Siegfried, E. and Thomas, G.H. 1988. Chromatin Structure and DNA Structure at the hsp26 locus of Drosophila. pp45-53 in 'Unusual DNA Structures', eds. Wells, R.D. and Harvey, S.C. (Springer-Verlag, New York, NY)
4. Thomas G.H., Siegfried E. and Elgin S.C.R. 1985. DNase I hypersensitive sites: a structural feature of chromatin associated with gene expression. pp77-101 in 'Chromosomal Proteins and Gene Expression' eds Reeck, G.R., Goodwin, G.H. and Puigdomenech, P. (Plenum Press. N.Y.)
5. Eissenberg J.C., Cartwright I.L., Thomas G.H. and Elgin S.C.R. 1985. Selected topics in chromatin structure. Ann. Rev. Genetics. 19:485-536

1. Thomas, G.H., Connerton, I.F. and Fincham, J.R.S. 1988. Molecular cloning, identification and transcriptional analysis of genes involved in acetate utilization in Neurospora crassa. Mol. Microbiology 2;599-606
2. Thomas, G.H. and Baxter, R.L. 1987. Analysis of mutational lesions of acetate metabolism in Neurospora crassa by 13C Nuclear Magnetic Resonance. J. Bact. 169;359-366

Humour Department

1. Thomas, G. 1988. Letter to the Editor. Focus 10(4);77
2. Thomas, G. and Phillips, M. 1999. The Charge of the Flight Brigade. Drosophila Information Service 82;viii-ix