dictyNews
Electronic Edition
Volume 37, number 3
July 29, 2011

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Abstracts
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BzpF is a CREB-like transcription factor that regulates spore maturation and 
stability in Dictyostelium

Eryong Huang, Shaheynoor Talukder, Timothy R. Hughes, Tomaz Curk, 
Blaz Zupan, Gad Shaulsky and Mariko Katoh-Kurasawa


Developmental Biology, in press

The cAMP response element-binding protein (CREB) is a highly conserved 
transcription factor that integrates signaling through the cAMP-dependent 
protein kinase A (PKA) in many eukaryotes. PKA plays a critical role in 
Dictyostelium development but no CREB homologue has been identified in 
this system. Here we show that Dictyostelium utilizes a CREB-like protein, 
BzpF, to integrate PKA signaling during late development. bzpF– mutants 
produce compromised spores, which are extremely unstable and germination 
defective. Previously, we have found that BzpF binds the canonical CRE 
motif in vitro. In this paper, we determined the DNA binding specificity of 
BzpF using protein binding microarray (PBM) and showed that the motif 
with the highest specificity is a CRE-like sequence. BzpF is necessary to 
activate the transcription of at least 15 PKA-regulated, late-developmental 
target genes whose promoters contain BzpF binding motifs. BzpF is 
sufficient to activate two of these genes. The comparison of RNA 
sequencing data between wild type and bzpF– mutant revealed that the 
mutant fails to express 205 genes, many of which encode cellulose-binding 
and sugar-binding proteins. We propose that BzpF is a CREB-like 
transcription factor that regulates spore maturation and stability in a 
PKA-related manner.


Submitted by: Mariko Katoh-Kurasawa [[log in to unmask]]
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Dictyostelium transfer RNA gene-targeting retrotransposons: 
Studying mobile element-host interactions in a compact genome 

Thomas Winckler, Jana Schiefner, Thomas Spaller, Oliver Siol

Universität Jena, Institut für Pharmazie, Lehrstuhl für Pharmazeutische 
Biologie, Semmelweisstrasse 10, 07743 Jena, Germany


Mobile Genetic Elements, in press

The model species of social amoebae, Dictyostelium discoideum, has a 
compact genome consisting of about two thirds protein-coding regions, 
with intergenic regions that are rarely larger than 1,000 bp. We 
hypothesize that the haploid state of D. discoideum cells provides defense 
against the amplification of mobile elements whose transposition activities 
would otherwise lead to the accumulation of heterozygous, potentially lethal 
mutations in diploid populations. We further speculate that complex 
transposon clusters found on D. discoideum chromosomes do not a priori 
result from integration preferences of these transposons, but that the 
clusters instead result from negative selection against cells harboring 
insertional mutations in genes. D. discoideum cells contain a fraction of 
retrotransposons that are found in the close vicinity of tRNA genes. 
Growing evidence suggests that these retrotransposons use active 
recognition mechanisms to determine suitable integration sites. However, 
the question remains whether these retrotransposons also cause 
insertional mutagenesis of genes, resulting in their enrichment at tRNA 
genes, which are relatively safe sites in euchromatic regions. Recently 
developed in vivo retrotransposition assays will allow a detailed, 
genome-wide analysis of de novo integration events in the D. discoideum 
genome.


Submitted by: Thomas Winckler [[log in to unmask]]
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Phylogeny-wide analysis of social amoeba genomes highlights ancient 
origins for complex intercellular communication.

Andrew J. Heidel, Hajara M. Lawal, Marius Felder, Christina Schilde, 
Nicholas R. Helps, Budi Tunggal, Francisco Rivero, Uwe John, 
Michael Schleicher, Ludwig Eichinger, Matthias Platzer, Angelika A. Noegel, 
Pauline Schaap, Gernot Glöckner

Genome Research, in press

Dictyostelium discoideum (DD), an extensively studied model organism 
for cell and developmental biology, belongs to the most derived group 4 
of social amoebas, a clade of altruistic multicellular organisms. To 
understand genome evolution over long time periods and the genetic basis 
of social evolution, we sequenced the genomes of Dictyostelium 
fasciculatum (DF) and Polysphondylium pallidum (PP), that represent the 
early diverging groups 1 and 2, respectively. In contrast to DD, PP and DF
have conventional telomere organisation and strongly reduced numbers 
of transposable elements. The number of protein coding genes is similar 
between species, but only half of them comprise an identifiable set of 
orthologous genes. In general, genes involved in primary metabolism, 
cytoskeletal functions and signal transduction are conserved, while genes 
involved in secondary metabolism, export and signal perception 
underwent large differential gene family expansions. This most likely 
signifies involvement of the conserved set in core cell and developmental 
mechanisms, and of the diverged set in niche- and species-specific 
adaptations for defence and food, mate and kin selection. Phylogenetic 
dating using a concatenated data set and extensive loss of synteny 
indicate that DF, PP and DD split from their last common ancestor at 
least 0.6 billion years ago.


Submitted by Gernot Gloeckner [[log in to unmask]]
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[End dictyNews, volume 37, number 3]