Dicty News
Electronic Edition
Volume 17, number 15
December 22, 2001
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
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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A Novel Dictyostelium Gene Encoding Multiple Repeats of Adhesion Inhibitor-
Like Domains has Effects on Cell-Cell and Cell-Substrate Adhesion.
Timothy R. Varney, Elisabeth Casademunt, Hoa N. Ho, Chere' Petty, Jayne
Dolman, and Daphne D. Blumberg*
Department of Biological Sciences, University of Maryland Baltimore County,
1000 Hilltop Circle, Baltimore, Maryland 21250
Developmental Biology in press
Abstract
The Dictyostelium protein AmpA (Adhesion modulation protein A) is
encoded by the gene originally identified by the D11 cDNA clone. AmpA
contains repeated domains homologous to a variety of proteins that influence
cell adhesion. The protein accumulates during development, reaching a
maximal level at the finger stage. Much of the AmpA protein is found
extracellularly during development, and in culminants AmpA is found in
association with Anterior-Like Cells. Characterization of an ampA- strain
generated by gene replacement reveals a significant increase in cell-cell
clumping when cells are starved in non-nutrient buffer suspensions.
Developing ampA- cells are also more adhesive to the underlying substrate
and are delayed in developmental progression, with the severity of the delay
increasing as cells are grown in the presence of bacteria or on tissue
culture dishes rather than in suspension culture. Reintroduction of the
ampA gene rescues the developmental defects of ampA- cells however
expression of additional copies of the gene in wild type cells results
in more severe developmental delays and decreased clumping in suspension
culture. We propose that the AmpA protein functions as an anti-adhesive
to limit cell-cell and cell-substrate adhesion during development and thus
facilitate cell migration during morphogenesis.
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A Gene Encoding a Novel Anti-Adhesive Protein is Expressed in Growing Cells
and Restricted to Anterior-Like Cells During Development of Dictyostelium.
Elisabeth Casademunt, Timothy R. Varney, Jayne Dolman, Chere' Petty and
Daphne D. Blumberg*
Department of Biological Sciences, University of Maryland Baltimore County,
1000 Hilltop Circle, Baltimore, Maryland 21250
Differentiation, in press
Abstract
The Dictyostelium gene ampA, initially identified by the D11 cDNA,
encodes a novel anti-adhesive-like protein. The ampA gene product inhibits
premature cell agglutination during growth and modulates cell-cell and cell-
substrate adhesion during development. Analysis of the promoter indicates
that cap site-proximal sequence directs ampA expression during both growth
and early development. Expression following tip formation is controlled by
more distal sequence, which contains TTGA repeats known to regulate prestalk
cell gene expression in other promoters.
Comparison of reporter gene expression and endogenous mRNA accumulation
indicate that during growth the ampA gene is expressed in an increasing
number of cells as a function of density. The number of cells expressing
the ampA gene drops as development initiates, but the cells that continue
to express the gene do so at high levels. These cells are initially
scattered throughout the entire aggregate. By the tip formation stage
however, the majority of ampA-expressing cells are localized to the mound
periphery, with only a few cells remaining scattered in the upper portion
of the mound. In the final culminant, ampA is expressed only in the upper
cup, lower cup and basal disc. Although reporter expression is observed
in cells that migrate anteriorly to a banded region just posterior to the
tip, expression is rarely observed in the extreme tip. AmpA protein
however, is localized to the tip as well as to ALCs during late
development. The results presented here suggest that ampA gene expression
is shut off in ALCs that continue along the prestalk differentiation
pathway before they are added to the primordial stalk.
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Deducing the Origin of Soluble Adenylyl Cyclase, a Gene Lost
in Multiple Lineages
Jeroen Roelofs and Peter J.M. Van Haastert
Department of Biochemistry, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, the Netherlands
Molecular Biology and Evolution, in press
The family of eukaryotic adenylyl cyclases consists of a very
large group of twelve transmembrane adenylyl cyclases and a
very small group of soluble adenylyl cyclase (sAC). Orthologs of
human sAC are present in rat, Dictyostelium and bacteria, but
absent from the completely sequenced genomes of Drosophila
melanogaster, Caenorhabditis elegans, Arabidopsis thaliana and
Saccharomyces cereviciae. sAC consists of two cyclase
domains and a long ~1000 amino acid C-terminal (sCKH)
region. This sCKH region and one cyclase domain have been
found in only four bacterial genes; the sCKH region was also
detected in bacterial Lux transcription factors and in complex
bacterial and fungal kinases. The phylogenies of the kinase and
cyclase domains are identical to the phylogeny of the
corresponding sCKH domain, suggesting that the sCKH region
fused with the other domains early during evolution in bacteria.
The amino acid sequences of sAC proteins yield divergence
times from the human lineage for rat and Dictyostelium that are
close to the reported divergence times of many other proteins in
these species. The combined results suggest that the sCKH
region was fused with one cyclase domain in bacteria, and a
second cyclase domain was added in bacteria or early
eukaryotes. The sAC was retained in a few bacteria and during
the entire evolution of the human lineage, but lost independently
from many bacteria and in the lineages to plants, yeast, worms
and flies. We conclude that within the family of adenylyl
cyclases, soluble AC was poorly fixed during evolution while
membrane bound AC has expanded to form the subgroups of
prevailing adenylyl and guanylyl cyclases.
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[End Dicty News, volume 17, number 15]