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dictyNews Volume 31 Number 03
dictyNews
Electronic Edition
Volume 31, number 3
July 18, 2008
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 dictyNews, 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 new family of transcription factors
Yoko Yamada+, Hong Yu Wang+, Masashi Fukuzawa, Geoffrey J. Barton and
Jeffrey G. Williams
+ Contributed equally
School of Life Sciences
University of Dundee DD1 5EH
U. K.
Development, in press
CudA, a nuclear protein required for Dictyostelium prespore-specific gene
expression, binds in vivo to the promoter of the cotC prespore gene. A
14nt region of the cotC promoter binds CudA in vitro and ECudA, an Entamoeba
CudA homologue, also binds to this site. The CudA and ECudA DNA binding site
contains a dyad and, consistent with a symmetrical binding site, CudA forms
a homodimer in the yeast two hybrid system. Mutation of CudA binding sites
within the cotC promoter reduces expression in prespore cells. The CudA and
ECudA proteins share a 120 amino acid core of homology and clustered point
mutations inserted in two highly conserved motifs within the ECudA core
region decrease its specific DNA binding in vitro. This region, the
presumptive DNA binding domain, is similar in sequence to domains in two
Arabidopsis proteins and one Oryza protein. Significantly, these are the
only proteins in the two plant species that contain an SH2 domain. Such a
structure, with a DNA binding domain located upstream of an SH2 domain,
suggests that the plant proteins are orthologous to metazoan STATs. Consistent
with this notion the DNA sequence of the CudA half binding site, GAA, is
identical to metazoan STAT half-sites; although the relative positions of the
two halves of the dyad are reversed. These results define a hitherto
unrecognised class of transcription factor and suggest a model for the
evolution of STATs and their DNA binding sites.
Submitted by: Jeff Williams [j.g.williams@dundee.ac.uk]
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From drought sensing to developmental control: evolution of cyclic AMP
signaling in social amoebas.
Allyson V. Ritchie1, Saskia van Es2, Celine Fouquet3 and Pauline Schaap*
College of Life Sciences, University of Dundee, UK.
Molecular Biology and Evolution, in press
Amoebas and other protists commonly encyst when faced with environmental
stress. While little is known of the signalling pathways that mediate
encystation, the analogous process of spore formation in Dictyostelid social
amoebas is better understood. In Dictyostelium discoideum, secreted
cyclic AMP (cAMP) mediates the aggregation of starving amoebas and induces
the differentiation of prespore cells. Intracellular cAMP acting on
cAMP-dependent protein kinase (PKA) triggers the maturation of spores and
prevents their germination under the prevalent conditions of high osmolality
in the spore head. The osmolyte-activated adenylate cyclase, ACG, produces
cAMP for prespore differentiation and inhibition of spore germination.
To retrace the origin of ACG function, we investigated ACG gene conservation
and function in species that span the dictyostelid phylogeny. ACG genes,
osmolyte-activated ACG activity and osmo-regulation of spore germination were
detected in species that represent the four major groups of Dictyostelia.
Unlike the derived species D.discoideum, many basal Dictyostelia have retained
the ancestral mechanism of encystation from solitary amoebas. In these species
and in solitary amoebas, encystation is independently triggered by starvation
or by high osmolality. Osmolyte-induced encystation was accompanied by an
increase in cAMP and prevented by inhibition of PKA, indicating that ACG and
PKA activation mediate this response. We propose that high osmolality signals
drought in soil amoebas and that developmental cAMP signaling in the
Dictyostelia has evolved from this stress response.
Submitted by: Pauline Schaap [p.schaap@dundee.ac.uk]
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[End dictyNews, volume 31, number 3]
