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dictyNews Volume 25 Number 08
Dicty News
Electronic Edition
Volume 25, number 8
October 14, 2005
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Identification of low frequency knockout mutants in Dictyostelium discoideum
created by single or double homologous recombination.
Steve J. Charette?, Sophie Cornillon, Pierre Cosson.
Universite de Geneve, Centre Medical Universitaire, Departement de Physiologie
Cellulaire et Metabolisme, 1 rue Michel Servet, CH-1211 Geneve 4, Switzerland.
Journal of Biotechnology, in press.
Generation and characterization of knockout clones is a widely used approach
to evaluate the specific function of a gene product in Dictyostelium
discoideum. The mutant clones are generally obtained by double homologous
recombination in the target gene. A frequent limitation to obtaining mutants
is the low frequency of homologous recombination. Here we present an easy
method to identify rare mutants, based on PCR analysis of pools of clones.
This method also allows the isolation of functional knockout mutants created
by a single homologous recombination event, which can be more frequent than
a double recombination event.
Submitted by: Steve Charette [charett2@etu.unige.ch]
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Receptor Occupancy on an Ellipsoidal Cell in the Presence of a Point Source
of a Chemoattractant
Igor Weber
Department of Molecular Biology, Ruder Boskovic Institute, Bijenicka 54,
HR-10000 Zagreb, Croatia
Journal of Chemical Information and Modeling, in press
Diffusion of a chemoattractant from a micropipet is routinely used to examine
the different aspects of a cell’s chemotactic response. To quantify the effect
of cell elongation on chemotactic sensitivity in the micropipet assay, the
chemoattractant concentration at the cell plasma membrane was determined by
solving the equation for diffusion from a point source in the presence of a
prolate ellipsoid of varying eccentricity. The results show that cell
elongation can significantly increase the difference in receptor occupancy
betweennear and far cell ends and thereby enhance the sensitivity of
chemotactic cells to shallow chemoattractant gradients.
Submitted by: Igor Weber [iweber@irb.hr]
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Cryoelectron Tomography: Implications for Actin Cytoskeleton Research
Igor Weber
Department of Molecular Biology, Ruder Boskovic Institute, Bijenicka 54,
HR-10000 Zagreb, Croatia
Croatica Chemica Acta, in press
Disclosing undistorted spatial organization of the actin cytoskeleton with
molecular resolution is fundamental for understanding the cellular
ultrastructure. Whereas important insights into the architecture of
microfilament networks have been gained by negative staining, critical
point drying, and freeze-fracturing methods, it is cryoelectron tomography
that provides, for the first time, a comprehensive three-dimensional view of
the intact actin cytoskeleton in situ. In particular, topological
relationships such as microfilament three-dimensional proximity, angles at
filament branching points, and modes of microfilament interaction with the
plasma membrane can be visualized with an unprecedented accuracy using this
technique. Further improvements are expected to bring the resolution into the
realm of 2–3 nm, where automatic pattern-recognition methods can be applied
to identify actin-binding complexes. Combining cryoelectron tomography with
ultra-fine immunolabeling and high-resolution fluorescence microscopy will
make it possible to correlate structural data on the nanometer scale with
molecular specificity and dynamical information.
Submitted by: Igor Weber [iweber@irb.hr]
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[End Dicty News, volume 25, number 8] 
