Thomas McGarry, MD PhD

Assistant Professor
Medicine

Unstable Regulatory Proteins

Curricula:
Cancer Biology
Developmental Biology
Molecular Biology and Genetics

E-mail:   t-mcgarry@northwestern.edu

Unstable Regulatory Proteins

Many biological processes are controlled through the degradation of a critical regulatory protein.  These processes include cell cycle transitions, inflammatory responses, circadian rhythms, and the response to hypoxia.  Most commonly the regulatory protein is destroyed by ubiquitin-dependent proteolysis.  In this pathway, a polymer of the small protein ubiquitin is covalently attached to the target protein then the ubiquitin-protein conjugate is destroyed by a multisubunit protease called the proteasome.  Ubiquitin conjugation reactions are carried out by a large and diverse family of enzymes that are collectively called ubiquitin protein ligases.  Each ligase targets a small set of specific substrates.

Our laboratory is interested in discovering the target proteins for ubiquitin protein ligases, since these are likely to be important regulatory proteins.  We used a small pool screening approach to identify two new targets for a ligase called the anaphase promoting complex (APC), which becomes active at the metaphase-anaphase transition in dividing cells.  One of these targets, securin, regulates chromosome separation. Securin inhibits a protease called separase that digests the cohesin proteins that hold chromosomes together.  The second target, Geminin, controls the extent of DNA replication by regulating the essential replication factor Cdt1.  We are currently generating a strain of mice that is missing Geminin in the bone marrow in order to see if the resulting genetic instability is carcinogenic.  We are also developing affinity methods to identify the targets of other ubiquitin protein ligases that have been implicated in human diseases such as von Hippel Lindau syndrome, Angelman syndrome, rheumatoid arthritis, and muscle atrophy.

Nuclear Reprogramming

Nuclear reprogramming is the process by which a differentiated somatic cell nucleus returns to the state of an undifferentiated embryonic nucleus.  Reprogramming is thought to involve the erasure of reversible epigenetic changes acquired during cell differentiation. There has been much interest recently in nuclear reprogramming because of its potential to provide a source of undifferentiated cells that could be used for therapy of diseases such as type I diabetes, Parkinson’s disease, spinal cord injury, and myocardial infarction. Reprogramming an individual patient’s own somatic cells would minimize the possibility that they would be rejected by the immune system.  Moreover, stem cells could be obtained without destroying human embryos, which many find ethically unacceptable.  Despite its obvious medical and scientific importance, the molecular basis of nuclear reprogramming is very poorly understood.

We study the mechanism of nuclear reprogramming using nuclear transplantation assays in Xenopus eggs.  The Xenopus system offers several experimental advantages for studying reprogramming at both the biochemical and functional level.  Nuclear transfer experiments are relatively simple to perform and extracts of eggs and oocytes that may have reprogramming activity are easy to obtain.  Our present focus is to isolate egg extracts that have reprogramming activity and to investigate the mechanism by using inhibitors and by depleting candidate reprogramming factors with antibodies.

Publications:

Kerns, S. L., Torke, S. J., Benjamin, J. M.,and McGarry, T. J. Geminin Prevents Re-Replication during Xenopus Develoment. Journal of Biological Chemistry 282 (8) 5514-21 (2007).

Benjamin, J. M., Torke, S. J., Demeler, B. and McGarry, T. J. Geminin has Dimerization, Cdt1-binding, and Destruction Domains that are Required for Biological Activity. Journal of Biological Chemistry 279 (44) 45957-68 (2004).

McGarry, T.J. Measurement of Geminin Activity in Xenopus Egg Extracts. Methods Mol, Biol. 296: 263-278 (2004).

McGarry, T.J., Kroll, K. L., and Kirschner, M.W. Geminin Gene and Protein. United States Patent #6,548,290 B1 (2003).

McGarry, T. J. Geminin-Deficiency causes a Chk1-Dependent G2 Arrest in Xenopus. Mol. Biol. Cell 13: 3662-3671 (2002).

Quinn, L., Herr, A., McGarry, T.J., and Richardson, H. E. The Drosophila Geminin Homolog is required for S phase-Mitosis Coordination during Development. Genes and Development15(20):2741-54 (2001).

Zou, H., McGarry, T. J., Bernal, T., and Kirschner, M. W. Identification of a Vertebrate Sister-Chromatid Separation Inhibitor Involved in Transformation and Tumorigenesis. Science 285: 418-422 (1999).

McGarry, T. J. and Kirschner, M. W. Geminin, an inhibitor of DNA replication, is degraded during mitosis. Cell 93: 1043-1053 (1998).

McGarry, T. J. Small pool screening. Trends in Cell Biology 7: 374 (1997).

PubMed website View Publications by Tom McGarry listed in the National Library of Medicine (PubMed).

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