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Actin polymerization and pseudopod extension during amoeboid chemotaxis (1988)

Condeelis, J. ; Hall, Anne ; Bresnick, Anne ; [et al.]

New York, NY : Wiley-Blackwell

Cell Motility and the Cytoskeleton 10 (1988), S. 77-90

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ISSN: 0886-1544

Keywords: amoeboid movement ; actin binding proteins ; sensory transduction ; actin nucleation ; Dictyostelium discoideum ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Medicine

Notes: Amoebae of the cellular slime mold Dictyostelium discoideum are an excellent model system for the study of amoeboid chemotaxis. These cells can be studied as a homogeneous population whose response to chemotactic stimulation is sufficiently synchronous to permit the correlation of the changes in cell shape and biochemical events during chemotaxis. Having demonstrated this synchrony of response, we show that actin polymerization occurs in two stages during stimulation with chemoattractants. The assembly of F-actin that peaks between 40 and 60 sec after the onset of stimulation is temporally correlated with the growth of new pseudopods. F-actin, which is assembled by 60 sec after stimulation begins, is localized in the new pseudopods that are extended at this time. Both stages of actin polymerization during chemotactic stimulation involve polymerization at the barbed ends of actin filaments based on the cytochalasin sensitivity of this response. We present a hypothesis in which actin polymerization is one of the major driving forces for pseudopod extension during chemotaxis. The predictions of this model, that localized regulation of actin nucleation activity and actin filament cross-linking must occur, are discussed in the context of current models for signal transduction and of recent information regarding the types of actin-binding proteins that are present in the cell cortex.

Additional Material: 7 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/cm.970100113

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Green algal microtubule-associated protein with a molecular weight of 90 kDa which bundles microtubules (1990)

Maekawa, Takami ; Ogihara, Satoshi ; Murofushi, Hiromu ; [et al.]

Springer

Protoplasma 158 (1990), S. 10-18

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ISSN: 1615-6102

Keywords: 90 kDa microtubule-associated protein ; Microtubule bundle ; Cytoplasmic streaming ; Dichotomosiphon tuberosus

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Cytoplasmic streaming in the freshwater, coencytic green alga,Dichotomosiphon tuberosus, is regulated by light. Conspicuous changes are observed in the number of microtubules cross-linked together in bundles when the cytoplasmic streaming is modulated by light. In an attempt to identify the cross-linker, we stainedD. tuberosus cells with antibodies specific for several different microtubules-associated proteins (MAPs) from vertebrates. Antibodies raised against bovine adrenal 190 kDa MAP stained the algal cells, and the pattern of staining was quite similar to that obtained with tubulin-specific antibodies. Examination by immunoelectron microscopy revealed that the antibodies specific for the 190 kDa microtubule-associated protein (MAP) were located along the microtubules. Western blotting demonstrated that the antibodies crossreacted with a peptide fromD. tuberosus with a molecular weight of about 90 kDa. This peptide was heat-stable, a property shared by the bovine 190 kDa MAP. Moreover, this 90 kDa peptide, crossreacted with antibodies raised against a synthetic peptide, identical to the tubulin-binding domain found in the 190 kDa MAP and in a tau protein. Partially purified 90 kDa protein fromD. tuberosus has the ability to bundle microtubules when mixed with a tubulin fraction fromD. tuberosus, in the presence of taxol. These results suggest that the 90 kDa protein fromD. tuberosus is a MAP that bundles microtubules.