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The central question behind our work is how the centrosome and primary cilium control cell function and influence development, and how defects in these structures cause a remarkable range of human disease, ranging from cancer, polycystic kidney disease, and obesity, to neurocognitive defects including mental retardation, schizophrenia, and dyslexia.

The centrosome consists of a pair of centrioles and pericentriolar material and organizes the cytoplasmic microtubules of most animal cells. Most importantly, the mother centriole (the older of the two in the pair) nucleates the formation of a primary cilium in most cells in the body. First seen by cell biologists in the 1950's, the primary cilium was ignored for many years until a combination of human and model organism genetics revealed that it is a critical sensory organelle with functions in many important processes. Defects in primary cilium structure and function cause a set of human conditions, called ciliopathies, that share a set of phenotypes that reflect the importance of the cilium in signaling pathways:

There are three main projects in the lab:

1) Ciliary biogenesis and function. In addition to the microtubules making up the interphase array and the mitotic spindle, most animal cells make a specialized microtubule structure, the primary cilium. This is a single, non-motile cilium that is able to act as a transducer of mechanical and chemical signals - sort of a cellular antenna. The microtubules of the ciliary axoneme grow directly from a centriole at their base, this centriole is often called a basal body. Some epithelial cells in the trachea, oviduct and brain produce hundreds of motile cilia on their surface, each with a centriole at their base. We are studying both the primary cilium and multi-ciliated cells for clues into ciliary structure and function, and centriole formation.

  • Anderson, C.T., and Stearns T. (2009) Centriole Age Underlies Asynchronous Primary Cilium Growth in Mammalian Cells. Curr. Biol. 19:1498-1502. (PDF)
  • Malone, A.M.D., Anderson, C.T., Tummala, P., Kwon, R.Y., Johnston, T.R., Stearns, T. and Jacobs, C.R. (2007) Primary cilia mediate mechanosensing in bone cells by a calcium-independent mechanism. PNAS 104:13325-13330. (PDF)
  • Vladar, E.K. and Stearns, T. (2007) Molecular characterization of centriole assembly in ciliated epithelial cells. J Cell Biol. 178:31-42. (PDF, Supplementary data)

2) Cell cycle control of centrosome duplication. We have shown that duplication of the centrosome, the microtubule organizing center of animal cells, is dependent on the cell cycle kinase cdk2, and on cell cycle-specific proteolysis. We are now working to determine the molecular mechanisms of centrosome duplication and to understand how centrosome duplication is controlled so that it happens once and only once per cell cycle. Cancer cells often have aberrant centrosome numbers, and we are investigating the relationship between aberrant centrosome number and the genome instability that is common in cancer cells.

  • Hatch, E.M., Kulukian, A., Holland, A.J., Cleveland, D.W., and Stearns, T. (2010) Cep152 interacts with Plk4 and is required for centriole duplication. J. Cell Biol. 191:721-729. (PDF, Commentary)
  • Mahjoub, M.R., Xie, Z., and Stearns, T. (2010) Cep120 is asymmetrically localized to the daughter centriole and is essential for centriole assembly. J. Cell Biol. 191:331-346. (PDF)
  • Tsou, M-F.B., Wang, W-J., George, K.A., Uryu, K., Stearns, T., and Jallepalli, P.V. (2009) Polo kinase and separase regulate the mitotic licensing of centriole duplication in human cells. Dev. Cell 17:344-354. (PDF, Supplementary data)
  • Tsou, M-F.B. and Stearns, T. (2006) Mechanism limiting centrosome duplication to once per cell cycle. Nature 442:947-951. PDF, Supplementary info, News and Views
  • Tsou, M-F.B. and Stearns, T. (2006) Controlling centrosome number: licenses and blocks. Curr. Opin. Cell Biol. 18:74-78. (PDF)
  • Wong, C. and Stearns, T. (2005) Mammalian cells lack checkpoints for tetraploidy, aberrant centrosome number, and cytokinesis failure. BMC Cell Biol. 6:6. (PDF)
  • Wong, C. and Stearns, T. (2003) Centrosome number is controlled by a centrosome-intrinsic block to reduplication. Nature Cell Biol. 5:539-544. (PDF)
  • Wong, C. and Stearns, T. (2003) A SAS-sy centriole in the cell cycle. Curr. Biol. 13:R351-352. (PDF)
  • Chang, P., Giddings, T. H., Winey, M., and Stearns, T. (2003) Epsilon-tubulin is required for centriole duplication and microtubule organization. Nature Cell Biol. 5:71-76. (PDF)
  • Stearns, T. (2001) Centrosome duplication: a centriolar pas de deux. Cell 105:417-420. (PDF)
  • Lacey, K. R., Jackson, P. K., and Stearns, T. (1999) Cyclin-dependent kinase control of centrosome duplication. Proc. Natl. Acad. Sci. 96:2817-2822. (PDF)
  • Freed, E., Lacey, K. R., Lyapina, S. A., Huie, P., Deshaies, R. J., Stearns, T., and Jackson, P. (1999) The SKP1 and CUL1 ubiquitin ligase components localize to the centrosome and regulate the centrosome duplication cycle. Genes Dev. 13:2242-2257. (PDF)

3) Microtubule nucleation and organization. Microtubules are polymers of tubulin, which is a heterodimer of alpha-tubulin and beta-tubulin. We have identified a remarkable complex of proteins associated with a third type of tubulin, gamma-tubulin. Gamma-tubulin and its associated proteins are localized to the centrosome and are critical for initiation, or nucleation, of microtubule assembly. The gamma-tubulin complex (gammaTuRC) is a very large, ring-shaped complex and contains at least 6 proteins in addition to gamma-tubulin. We are determining the role of gamma-tubulin and its associated proteins in microtubule nucleation and organization.

  • Haren, L., Stearns, T. and Luders, J. (2009) Plk1-dependent recruitment of gamma-tubulin complexes to mitotic centrosomes involves multiple PCM components. PLoS ONE. 4:e5976. (PDF)
  • Luders, J., Patel, U.K., and Stearns, T. (2006) GCP-WD is a gamma-tubulin targeting factor required for centrosomal and chromatin-mediated microtubule nucleation. Nature Cell Biol. 8:137-147. (PDF)
  • Aldaz, H., Rice, L.M., Stearns, T., and Agard, D.A. (2005) Insights into microtubule nucleation from the crystal structure of human gamma-tubulin. Nature 435:523-527. (PDF)
  • Louie, R.K., Bahmanyar, S., Siemers, K.A., Votin, V., Chang, P., Stearns, T., Nelson, W.J., and Barth, A.I. (2004) Adenomatous polyposis coli and EB1 localize in close proximity of the mother centriole and EB1 is a functional component of centrosomes. J Cell Sci. 117:1117-1128. (PDF)
  • Patel U., Stearns T. (2002) Quick Guide: Gamma-Tubulin. Curr Biol. 2002 12:R408. (PDF)
  • Murphy, S.M., Preble, A.M., Patel, U.K., O'Connell, K.L., Dias, D.P., Moritz, M., Agard, D., Stults, J.T., and Stearns, T. (2001) GCP5 and GCP6: Two new members of the human gamma-tubulin complex. Mol. Biol. Cell 12:3340-3352. (PDF)
  • Jeng, R. and Stearns, T. (1999) Gamma-Tubulin complexes: size does matter. Trends Cell Biol. 9:339-342. (PDF)
  • Murphy, S. M., Urbani, L., and Stearns, T. (1998) The mammalian gamma-tubulin complex contains homologs of the yeast spindle pole body components Spc97p and Spc98p. J. Cell Biol. 141:663-674. (PDF)
  • Leask, A. and Stearns, T. (1998) Expression of amino- and carboxy-terminal gamma- and alpha-tubulin mutants in cultured epithelial cells. J. Biol. Chem. 273:2661-2668. (PDF)
  • Leask, A., Obrietan, K.,  and Stearns, T. (1997) Synaptically-coupled central nervous system neurons lack centrosomal gamma-tubulin.  Neuroscience Letters 229:17-20.
  • Marschall, L. G., Jeng, R. L., Mulholland, J. and Stearns, T. (1996) Analysis of Tub4p, a yeast gamma-tubulin-like protein: implications for microtubule-organizing center function. J. Cell Biol. 134:443-454.
  • Stearns, T. and Kirschner, M. (1994) In vitro reconstitution of centrosome assembly and function: the central role of gamma-tubulin. Cell 76:623-638.