Daniel J. Lew, Ph.D.

Daniel J. Lew, Ph.D. James B. Duke Professor of Pharmacology and Cancer Biology
Professor of Genetics

Duke University School of Medicine
C359 LSRC
Box 3813
Durham, NC 27710

Phone: 919-613-8627
E-mail:
Website

Research Interests

Our research interests focus on the control of cell polarity. Cell polarity is a nearly universal feature of eukaryotic cells. A polarized cell usually has a single, clear axis of asymmetry: a "front" and a "back." This general description encompasses an enormous variety of polarized morphologies, differing between cell types and organisms. Thus, it was not clear, a priori, whether regulation of "cell polarity" would entail diverse pathways linked to the diverse morphologies, or a single "master" pathway that would coordinate differing machineries in different cells. In the past several years it has become apparent that the highly conserved Rho-family GTPase Cdc42, first discovered in yeast, is a component of such a master pathway, employed time and again to promote polarity in different contexts.

Most cells know which way to polarize. Concentration gradients of attractants, repellents, nutrients, or pheromones reveal the optimal directions for successful attack, escape, feeding, or mating. However, cells can and do polarize even when deprived of directional cues, choosing a random axis and committing to it as if they knew where they were going. This process, called "symmetry breaking", reflects the presence of a core internal polarity program. But how does this core program persuade all polarity molecules to pick the same, randomly oriented, front and back?

Symmetry breaking is thought to reflect the action of positive feedback loops that reinforce inequalities in the local concentrations of polarity factors, so that stochastic fluctuations are amplified into a single dominating asymmetry. This idea was first suggested by the mathematician Alan Turing in 1952, but the molecular nature of the feedback loops involved in cell polarity remained unknown.

We use the tractable budding yeast as a model system. Because the genes and processes we study are highly conserved, we anticipate that learning the answers to fundamental questions in yeast will be relevant and informative for a wide range of organisms. Our work combines molecular genetics, cell biology, and mathematical modeling, and has suggested a mechanism whereby a cluster of Cdc42 molecules at the cell cortex can "grow" by positive feedback (reviewed in Johnson et al. 2011). This raised a number of questions, including:

  • Why is there one and only one "front"? Positive feedback can explain why a polarity cluster grows, but it does not automatically explain why there is not more than one such cluster: what would prevent stochastic fluctuations from initiating growth of multiple "fronts?" Our findings suggest that several Cdc42 clusters can indeed start to grow, but then they compete with each other and only one winner emerges. We would like to understand how competition works, and how it is inactivated on those rare occasions when specialized cells establish more than one polarity axis.
  • How is polarity turned on and off? In yeast, cell polarity is coordinated with the cell cycle, and we would like to understand how polarization is initially triggered and then shut off. 

  • How does Cdc42 organize the cytoskeleton? The Cdc42 cluster causes actin filaments to assemble into thick "cables" oriented towards the cluster, and septin filaments to assemble into a ring around the cluster. We would like to understand how these structures are built and what role Cdc42 plays. 

  • How is polarity guided by pheromone gradients? Yeast cells are non-motile, but they are able to grow projections towards mating partners. Cells of opposite mating type secrete peptide pheromones, which are detected by G-protein-coupled receptors and turn on a mating response that includes projection formation in responsive cells. Cells are able to track even very shallow pheromone gradients to find and fuse with mating partners. We would like to understand how the cells can recognize the faint gradient signal from the surrounding noise.

 

Representative Publications

Woods, B., Lai, H., Wu, C.-F., Zyla, T.R., Savage, N.S., and Lew, D.J. Parallel actin-independent recycling pathways polarize Cdc42 in budding yeast. Current Biology 26: 2114-2126 (2016).

Kang, H. and Lew, D.J. How do cells know what shape they are? Current Genetics DOI 10.1007/s00294-016-0623-1 (2016).

McClure A.W., Minakova M., Dyer J.M., Zyla T.R., Elston T.C., Lew D.J. Role of Polarized G Protein Signaling in Tracking Pheromone Gradients. Dev. Cell 35(4):471-82 (2015).

Wu C.F., Chiou J.G., Minakova M., Woods B., Tsygankov D., Zyla T.R., Savage N.S., Elston T.C., Lew D.J. Role of competition between polarity sites in establishing a unique front. Elife 4:e11611 (2015).

Kuo C.C., Savage N.S., Chen H., Wu C.F., Zyla T.R., Lew D.J. Inhibitory GEF phosphorylation provides negative feedback in the yeast polarity circuit. Current Biology 24(7):753-9 (2014)

Wu C.F., Lew D.K. Beyond symmetry-breaking: competition and negative feedback in GTPase regulation Trends in Cell Biology 23(10):476-83 (2013). *Top ten editorial board favorite article of 2013

Dyer J.M., Savage N.S., Jin M., Zyla T.R., Elston T.C., Lew D.J. Tracking shallow chemical gradients by actin-driven wandering of the polarization site Current Biology 23(1):32-41 (2013).

Howell A.S., Jin M., Wu C.F., Zyla T.R., Elston T.C., Lew D.J. Negative feedback enhances robustness in the yeast polarity establishment circuit Cell 149(2):322-33 (2012).

Johnson J.M., Jin M., Lew D.J. Symmetry breaking and the establishment of cell polarity in budding yeast Current Opinion in Genetics & Development 21(6):740-6 (2011).