BACTERIAL CYTOSKELETON AND CELL CYCLE REGULATION
	Christine Jacobs-Wagner, Ph.D. Maxine F. Singer Professor of Molecular, Cellular & Developmental Biology Email: christine.jacobs-wagner@yale.edu Room: KBT 1032 Phone: (203) 432-5170 Lab Web site Ph.D. University of Liege, Belgium 1996

Fig. 1: Polar localization of DivK-GFP.

Fig. 2: Three-dimensional representation of FRET signals (peaks) between DivJ-mYFP and DivK-mCFP at the stalked pole, indicative of a localized interaction between these two proteins. Fig. 3: Three-dimensional representation of a helical C. crescentus cell (green) with a helical filament of crescentin (red).

The research program in our laboratory addresses:

1. mechanisms that govern cell cycle control and the acquisition and propagation of asymmetry using a simple prokaryotic model system, and
2. the bacterial cytoskeleton that supports cell shape.

1) Cell cycle control and asymmetry: Caulobacter crescentus provides a unique system to study the genetic circuitry that controls the bacterial cell cycle because of its small genome size, its amenability to genetics and biochemistry, and the ease to obtain synchronized cell populations. In addition to the analysis of cell cycle progression, Caulobacter offers access to the study of cell differentiation and asymmetry since the normal progression through its cell cycle is accompanied by a series of transitions that produces distinct cell types. In Caulobacter, two-component signal transduction proteins are at the heart of cell cycle control. The DNA-binding transcriptional regulator CtrA is essential for the regulation of critical cell cycle and morphogenetic events such as initiation of DNA replication, cell division, DNA methylation, and polar organelle biogenesis. The temporal and spatial regulation of this global regulator is rigorously controlled through cell cycle-regulated phosphorylation and proteolysis. Strikingly, several signaling proteins that control CtrA activity during the cell cycle dynamically localize to discrete positions in the cell as a function of cell cycle progression, indicating that the dynamic localization of signaling proteins provides yet another level of cell cycle regulation. We are now asking: How do proteins move to targeted addresses in the cell? Is the specific cellular address critical to the function of the localized protein? If positioning is a controlling mechanism, how does it work? Using cell imaging techniques, we are studying protein dynamics in living cells. We are also identifying factors that control the temporally regulated localization of these proteins using genetics.

2) Bacterial cytoskeleton: How do cells create and maintain a defined shape? This is a fundamental problem from bacteria to humans. In higher organisms, intermediate filaments (IF), which constitute one of the three major components of the eukaryotic cytoskeleton, play an important role in cell shape. We have identified a bacterial equivalent to IF proteins, named crescentin, whose cytoskeletal function is required for the vibrioid and helical shapes of the bacterium Caulobacter crescentus. Without crescentin, the cells adopt a straight-rod morphology. Crescentin has characteristic features of IF proteins including the ability to assemble into filaments in vitro without energy or cofactor requirements. In vivo, crescentin forms a helical structure that colocalizes with the inner cell curvatures beneath the cytoplasmic membrane. Using microscopy, genetics, and biochemistry, we are investigating the mechanism by which crescentin filaments cause cell curvature. An ongoing study aims to characterize the assembly properties of crescentin filaments, in comparison with those of animal IFs. Future studies are planned for identifying other cytoskeletal and cytoskeleton-associated factors involved in bacterial cell shape.

			Figure 4: Scheme of C. crescentus cell cycle.

Selected Publications

Lam, H., Matroule, J.-Y., and Jacobs-Wagner, C. (2003) The asymmetric spatial distribution of bacterial signal transduction proteins coordinates cell cycle events. Dev Cell 5, 149-159.

Ausmees, N., Kuhn, J. R., and Jacobs-Wagner, C. (2003) The Bacterial Cytoskeleton: An Intermediate Filament-like Function in Cell Shape. Cell 115:705-13.

Ausmees N, Jacobs-Wagner C. (2003) Spatial and temporal control of differentiation and cell cycle progression in Caulobacter crescentus. Annu Rev Microbiol, 57:225-47.

Jacobs-Wagner, C. (2004) Regulatory proteins with a sense of direction: Cell cycle signaling network in Caulobacter. Mol Microbiol 51:7-13.

Matroule J.Y., Lam H., Burnette D.T., Jacobs-Wagner C. (2004) Cytokinesis monitoring during development: Rapid pole-to-pole shuttling of a signaling protein by localized kinase and phosphatase in Caulobacter. Cell 118: 579-90.

Cabeen, M.T. and Jacobs-Wagner, C. Bacterial cell shape. Nature Rev Microbiol 2005 3: 601-10.

Lam, H., Schofield, W.B., and Jacobs-Wagner, C. (2006) A landmark protein essential for establishing and perpetuating the polarity of a bacterial cell. Cell 124:1011-23

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