page_title: Caulobacter crescentus
section_title: Cell polarity regulation
hierarchical_section_title: Caulobacter crescentus / Cell polarity regulation
caption_attribution_description: English: PodJ protein (purple) is at the flagellar pole, while DivJ protein (red) is at the stalk.TipN is found at new poles (newly septated).
context_page_description: Caulobacter crescentus is a Gram-negative, oligotrophic bacterium widely distributed in fresh water lakes and streams. The taxon is more properly known as Caulobacter vibrioides.
  Caulobacter is an important model organism for studying the regulation of the cell cycle, asymmetric cell division, and cellular differentiation. Caulobacter daughter cells have two very different forms. One daughter is a mobile "swarmer" cell that has a single flagellum at one cell pole that provides swimming motility for chemotaxis. The other daughter, called the "stalked" cell, has a tubular stalk structure protruding from one pole that has an adhesive holdfast material on its end, with which the stalked cell can adhere to surfaces. Swarmer cells differentiate into stalked cells after a short period of motility. Chromosome replication and cell division only occurs in the stalked cell stage. Its name derives from its crescent shape caused by the protein crescentin. Its use as a model originated with developmental biologist Lucy Shapiro.
context_section_description: In C. crescentus, cell polarity is readily apparent by the assembly of polar organelles and by the polarization of the division plane, which results in the generation of stalked progeny that are longer than swarmer progeny. The formation of new cell poles at division implies that cell polarity must be re-established in the stalked progeny and reversed in the swarmer progeny.
  The C. crescentus life cycle is governed by regulators such as TipN , a cell cycle protein studied by students of Christine Jacobs-Wagner at Yale University, their data strongly suggest a model in which TipN regulates the orientation of the polarity axis by providing a positional cue from the preceding cell cycle. In this model TipN specifies the site of the most recent division by identifying the new pole. The cell uses this positional information as a source of intracellular asymmetry to establish and maintain the orientation of the polarity axis, which is crucial for polar morphogenesis and division. Recruitment of TipN to the nascent poles at the end of the division cycle redefines the identity of the poles and resets the correct polarity in both future daughter cells (with a polarity reversal in the swarmer cell).
  The cell cycle–regulated synthesis and removal of these polarly localized structures have provided a rich playground for the identification of landmark proteins important for their proper localization. The landmark protein TipN is essential for the proper placement of the flagellum. 
  TipN has two transmembrane regions in the N-terminal region and a large C-terminal coiled-coil domain. TipN homologues are present in other alpha-proteobacteria. TipN localizes to the new pole in both daughter cells after division and relocalizes to the cell division site in the late predivisional cell. Therefore, both daughter cells have TipN at the new pole after division.
  Mutants lacking TipN make serious mistakes in development. instead of making a single flagellum at the correct cell pole , the cell makes multiple flagella at various locations , even on the stalk.
  Cell development involves many such proteins working together. Fig#1 shows how TipN interact with two other polar proteins : the flagellar marker PodJ , and the stalk marker DivJ.
caption: Fig#1
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