Weiner Lab

How cells establish polarity and guide movement
Movie 1. Propagating waves of Hem-1 (component of the Scar/WAVE complex, a highly conserved regulator of cellular morphogenesis) organize neutrophil polarity and motility

Many eukaryotic cells have the capacity to polarize and migrate in response to external gradients of chemoattractant. Directed motility is essential for single-celled organisms to hunt and mate, axons to find their way in the developing nervous system, and cells in the innate immune system to find and kill invading pathogens. We are only beginning to understand the circuitry of the internal 'compass' used by eukaryotic cells to regulate polarity during chemotaxis. Our research focuses on identifying key missing components of the cellular compass and determining how the overall signaling network is wired together to coordinate the many activities involved in directed cell polarity.  Our model systems for these studies are neutrophils (one of nature's master migratory cells) and neutrophil lysates, which contain very high concentrations of many proteins that regulate polarity.

Movie 2 (left) shows human neutrophils following moving gradient of chemoattractant. Figure 1 (right) shows human neutrophil polarizing in response to gradient of chemoattractant (to right of field).

Part of our research focuses on identifying core circuits of cell polarity. We discovered a positive feedback loop involving the GTPase Rac, the lipid PIP₃, and actin polymers that plays a central role in generating neutrophil polarity.   Analogous feedback loops are now known to be essential for polarity in cells ranging from yeast to Dictyostelium to neutrophils.  To uncover novel components of this circuit, we used a combination of classical protein purification and reverse genetics to identify a set of protein complexes (Hem-1 containing complexes) that are essential for the feedback loops that control cell polarity in neutrophils. We suspect this scaffold may orchestrate an entire program of polarity effectors that act at the leading edge during chemotaxis, and we are currently dissecting the inputs and outputs of this essential polarity circuit.

We recently discovered an actin-based wave generator that appears to organize neutrophil polarity and motility. Using total internal reflection fluorescence (TIRF) microscopy, we find that Hem-1 complexes (including the Scar/WAVE complex-- a highly conserved regulator of cell morphogenesis), which were previously thought to be generally asymmetric, instead exhibit strong local spatial patterns with multiple propagating waves that organize the leading edge (See Movie 1 at top of page). Similar to action potentials and calcium waves, these polarity waves are self-renewing and generate their own inhibitors to produce directional wave propagation.  Specifically, membrane-bound Hem-1 both (1) recruits additional cytosolic Hem-1 to the membrane and (2) induces actin polymerization, which ultimately removes Hem-1 from the membrane.  We can reproduce the properties of these waves with a model containing a small number of variables that unites the current conception of global cell polarity with the properties of biological wave generators. This simple wave-generating circuit could account for several previously inexplicable behaviors of motile cells including coordinated behavior of the leading edge, cells that flow around boundaries, and dynamic polarity.  Because motility is a direct consequence of these propagating waves, Hem-1 waves represent a new framework for understanding cell migration.

We are developing techniques to deconstruct and reconstitute key polarity circuits in vitro and spatially manipulate and monitor signaling in vivo in our quest to understand how these amazing migratory cells work. This knowledge is essential if we are to ultimately control inflammation, cancer metastasis, and other processes that depend on properly guided cell movement.

Selected Publications:

Weiner, O.D., G. Servant, M.D. Welch, T.J. Mitchison, J.W. Sedat, and H.R. Bourne (1999) Spatial control of actin polymerization during neutrophil chemotaxis, Nature Cell Biol., 1: 75-81.

Servant, G.*, O.D. Weiner*, P. Herzmark, T. Bhalla, J.W. Sedat, and H.R. Bourne (2000). Polarization of chemoattractant receptor signaling during neutrophil chemotaxis. Science, 287: 1037-1040. (*equal contribution)

Weiner, O.D. (2002) Regulation of cell polarity during eukaryotic chemotaxis: the chemotactic compass. Current Opin. Cell Biol., 14: 196-202.

Bourne, HR and O.D. Weiner (2002) Cell polarity: a chemical compass. Nature, 419: 21.

Weiner, O.D., P.O. Neilsen, G.D. Prestwich, M.W. Kirschner, L.C. Cantley, and H.R. Bourne. (2002) A PI(3,4,5)P3/ Rho GTPase positive feedback loop regulates neutrophil polarity, Nature Cell Biol., 4: 509-513.

Weiner O.D.*, M.C. Rentel*, A. Ott, G.E. Brown, M. Jedrychowski, M.B. Yaffe, S.P. Gygi, L.C. Cantley, H.R. Bourne, and M.W. Kirschner (2006) Hem-1 complexes regulate multiple polarity effectors at the leading edge of migrating neutrophils, PLoS Biol., 4(2): e38. (*equal contribution)

Weiner O.D., W.A. Marganski, L.F. Wu, S.J. Altschuler, and M.W. Kirschner. (2007).  An actin-based wave generator organizes cell motility, PLoS Biol., 5(9): e221.

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