CSM News
Electronic Edition
Volume 4, number 1
January 14, 1995

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu.

Back issues of CSM-News, the CSM Reference database and other useful
information is available by anonymous ftp from worms.cmsbio.nwu.edu
[165.124.233.50], via Gopher at the same address, or by World Wide Web
through www.nwu.edu.

===========
 Abstracts
===========

Bsr-REMI: an Improved Method for Gene Tagging Using a New Vector in
Dictyostelium

Takahiro Morio, Hiroyuki Adachi*, Kazuo Sutoh*, Kaichiro Yanagisawa 
and Yoshimasa Tanaka

Institute of Biological Sciences, University of Tsukuba, Tsukuba, 
Ibaraki 305, Japan
*Department of Life Sciences, Graduate School of Arts and Sciences, 
University of Tokyo, Meguro-ku,Tokyo 153, Japan

Journal of Plant Research, in press

Abstract

   Using a plasmid pBsr2 which carries a blasticidin S-resistant gene,
we have improved the method of REMI (restriction enzyme-mediated
integration) provided for insertional mutagenesis in the cellular
slime mold Dictyostelium discoideum (bsr-REMI). It is applicable to
the axenic strain KAx-3 and takes only 4-5 days to obtain transformant
clones with good efficiency. We found that single copy of the vector
DNA was integrated randomly in 91% of the stable transformed clones.
These results show that bsr-REMI is a convenient and useful technique
for gene tagging in this organism.

--------------------------------------------------------------------

A talin homologue of Dictyostelium rapidly assembles at the leading
edge of cells in response to chemoattractant.

Martina Kreitmeier, Guenther Gerisch, Christine Heizer, and Annette 
Mueller-Taubenberger.

J. Cell Biol., in press

Abstract

   In an attempt to identify unknown actin-binding proteins in cells
of Dictyostelium discoideum that may be involved in the control of
cell motility and chemotaxis, monoclonal antibodies were raised
against proteins that had been enriched on an F-actin affinity matrix.
One antibody recognized a protein distinguished by its strong
accumulation at the tips of filopods.  These cell-surface extensions
containing a core of bundled filaments are rapidly protruded and
retracted by cells in the growth-phase stage. The protein of 269 kDa
turned out to resemble mouse fibroblast talin (Rees et al., 1990) in
its primary structure. The fit is best among the first 400 amino acid
residues of the N-terminal region where identity between the two
protein is 44 per cent, and the last 200 amino acid residues of the
C-terminal region with 36 per cent identity. In the elongated cells of
the aggregation stage the Dictyostelium talin is accumulated at the
entire front where also F-actin is enriched. Since this protein exists
in a soluble state in the cytoplasm, mechanisms are predicted that
cause accumulation at sites of the cell where a front is established.
Evidence for receptor-mediated accumulation was obtained by local
stimulation of cells with cAMP. When a new front was induced by the
chemoattractant, the talin accumulated there within half a minute,
indicating a signal cascade in Dictyostelium responsible for assembly
of the talin beneath sites of the plasma membrane where
chemoattractant receptors are strongly activated.  The ordered
assembly of the talin homologue together with actin and a series of
other proteins is considered to play a key role in chemotactic
orientation.

--------------------------------------------------------------------

A MAP kinase necessary for receptor-mediated activation of adenylyl
cyclase in Dictyostelium

Jeffrey E. Segall1*, Adam Kuspa2,3 , Gad Shaulsky2, Maria Ecke1,5,
Mineko Maeda2,4, Chris Gaskins2, Richard A. Firtel2, and William F.
Loomis2 

1Department of Anatomy and Structural Biology Albert Einstein College
of Medicine Bronx, NY 10461

2Center for Molecular Genetics Department of Biology University of
California at San Diego La Jolla, CA 92093-0322

3Present address: Department of Biochemistry Baylor College of
Medicine, Houston, TX 77030

4Present address: Department of Biology College of General
Education Osaka University 1-1 Machikaneyama-cho, Toyonaka-shi
Osaka 560 Japan

5Present address: Department of Cell Biology Max Planck Institute for
Biochemistry 8033 Martinsried Germany

ABSTRACT 

Analysis of a developmental mutant in Dictyostelium discoideum that is
unable to initiate morphogenesis has shown that a protein kinase of
the MAP kinase/ERK family affects relay of the cAMP chemotactic signal
and cell differentiation.  Strains in which the locus encoding ERK2 is
disrupted respond to a pulse of cAMP by synthesizing cGMP normally but
show little synthesis of cAMP.  Since mutant cells lacking ERK2
contain normal levels of both the cytosolic regulator of adenylyl
cyclase (CRAC) and manganese-activatable adenylyl cyclase, it appears
that this kinase is important for receptor-mediated activation of
adenylyl cyclase.

-----------------------------------------------------------------------

[End CSM-News.  Volume 4, number 1]