Specificity in chemotaxis

So far, there are two best documented examples of specificity in chemotaxis and subsequent differentiation of oomycete zoospores by host plant signals. The first one is the attraction, encystment and germination of A. cochlioides zoospores to a rare flavone, cochliophilin A (3), and the other one is Ph. sojae zoospores to isoflavones daidzein (4) and genistein (5)... 

Methylation. A group of enzymes, referred to as the protein methyltrans-ferases, use S-adenosylmethionine to methylate certain proteins. For example, one type of methyltransferase found in E. coli and related bacteria methylates glutamate residues in membrane-bound chemoreceptors. The methyltransferase and a methylesterase are components in a methylation/demethylation process, which plays a role in a signal transduction mechanism involved in chemotaxis. (Recall that the capacity of a living cell to respond to certain environmental cues by moving toward or away from specific molecules is referred to as chemotaxis.)... 

J. (1969) Escherichia coli mutants defective in chemotaxis toward specific chemicals. Proc. Natl. Acad. Sci. USA 64, 1300-1307. 

E. coli has five chemotaxis-specific receptors, MCPs, which sense a variety of stimuli. Of these receptors, Aer appears to be the most specific in... 

The structures of most of the binding proteins involved in chemotaxis have been solved both in the free and ligand-bound states (see [524] for a review). From these studies it became clear that, upon binding the ligand, the receptor undergoes a massive conformational change, as a result of which the probability of the protein to be in its open form is reduced and it converts to a closed form. The closed form of the receptor, unlike its open form, possesses a spatial structure that enables it to bind specifically to its cognate MCP (e.g., [361, 383, 643, 689, 810]). 

M. mnthus development. The key to bacterial coordinated behavior resides in the ability of a cell to receive, interpret, and respond to these signals. Relaying the information may require direct contact between the donor and the recipient cells or it may be carried out from a distance, i.e., by means of diffusible molecules, which are detected through their interaction with specific receptors. As discussed in Chapter 3, bacterial chemotaxis is the most completely understood of the bacterial sensory transduction systems. While the role of chemotaxis in intercellular communication is still not clear, in some cases, mutants deleted for chemotaxis genes fail to carry out one or another of the processes mentioned above. Components of the chemotaxis system seem to play a role in swarming motility, pattern formation, and myxobacterial development. In fact, it appears that certain chemotaxis functions have been recruited by certain species to mediate intercellular communication. In this chapter, we review some examples, and provide evidence as well as hypotheses concerning a role for proteins and systems involved in chemotaxis in multicellular behavior. 

Is sperm chemotaxis specific, i.e., are the chemoattractants specific for each species or are there chemoattractants common to several species There is no single answer to this question. With some exceptions, species specificity appears to be the rule in marine species [102, 103]. There, the gametes are released in to seawater, and gametes of different species may be in close proximity. Therefore, in these cases, chemotaxis may be needed as one of the means to avoid interspecies fertilization. Indeed, in some marine groups (e.g., sea urchins, hydromedusae and certain ophiuroids), the specificity of sperm chemotaxis is very high. In other groups (e.g., starfish), the specificity is at the family level and, within the family, there is no specificity. In contrast, in mollusks, there appears to be no specificity at all ([35,102,103] and references therein). 

What is the situation in mammals The need for species specificity in mammalian sperm chemotaxis is not obvious. On the one hand, specificity might be desired as a mean to avoid cross-species fertilization. 

Vinca alkaloids (vincristine, vinblastine, vindesine) are derived from the periwinkle plant (Vinca rosea), they bind to tubulin and inhibit its polymerization into microtubules and spindle formation, thus producing metaphase arrest. They are cell cycle specific and interfere also with other cellular activities that involve microtubules, such as leukocyte phagocytosis, chemotaxis, and axonal transport in neurons. Vincristine is mainly neurotoxic and mildly hematotoxic, vinblastine is myelosuppressive with veiy low neurotoxicity whereas vindesine has both, moderate myelotoxicity and neurotoxicity. 

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