Dicty News
Electronic Edition
Volume 20, number 3
March 1, 2003

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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Villidin, a novel WD-repeat and villin related protein from 
Dictyostelium, is associated with membranes and the cytoskeleton

Annika Gloss, Francisco Rivero, Nandkumar Khaire, Rolf Mller, William 
F. Loomis, Michael Schleicher and Angelika A. Noegel

Mol. Biol. Cell, in press

Villidin is a novel multidomain protein (190 kDa) from Dictyostelium 
amoebae containing WD repeats at its N-terminus , three PH domains in 
the middle of the molecule, five gelsolin-like segments at the C-terminus, 
followed by a villin-like headpiece. Villidin mRNA and protein are present 
in low amounts during growth and early aggregation, but increase during 
development and reach their highest levels at the tipped mound stage. The 
protein is present in the cytosol as well as in the cytoskeletal and 
membrane fractions. GFP-tagged full length villidin exhibits a similar 
distribution as native villidin including a distinct colocalization with 
Golgi structures. Interestingly, GFP fusions with the gelsolin/villin-like 
region are uniformly dispersed in the cytoplasm, whereas GFP fusions of 
the N-terminal WD repeats codistribute with F-actin and are associated 
with the Triton-insoluble cytoskeleton. Strains lacking villidin due to 
targetted deletion of its gene grow normally and can develop into fruiting 
bodies. However, cell motility is reduced during aggregation and phototaxis 
is impaired in the mutant strains. We conclude that villidin harbors a 
major F-actin binding site in the putative propellerN-terminal domain and 
not in the villin-like region as expected; association of villidin with 
vesicular membranes suggests that the protein functions as a linker between 
membranes and the actin cytoskeleton.

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Changing patterns of gene expression in prestalk cell subtypes of 
Dictyostelium recognized by in situ hybridization with genes from 
microarray analyses.

Mineko Maeda1*, Haruyo Sakamoto1, Negin Iranfar2, Danny Fuller2, Toshinari 
Maruo1, Satoshi Ogihara1, Takahiro Morio3, Hideko Urushihara 3, Yoshimasa 
Tanaka 3, and William F. Loomis 2*

1) Department of Biology, Graduate School of Science, Osaka University, 
Machikaneyama 1-16, Toyonaka, Osaka 560-0043, Japan,
2) Cell and Developmental Biology, Division of Biological Sciences,
University of California San Diego, 9500 Gilman Drive, La Jolla, CA92093, 
USA
3) Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 
305-8572, Japan

Eukaryotic Cell (in press)

ABSTRACT

We used microarrays carrying most of the genes that are developmentally 
regulated in Dictyostelium to discover those that are preferentially expressed 
in prestalk cells. Prestalk cells are localized at the front of slugs and 
play crucial roles in morphogenesis and slug migration. Using whole-mount 
in situ hybridization we were able to verify 104 prestalk genes.  Three of 
these were found to be expressed only in cells at the very front of slugs, 
the PstA cell type.  Another 10 genes were found to be expressed in the small 
number of cells that form a central core at the anterior, the PstAB cell 
type. The rest of the prestalk specific genes are expressed in PstO cells 
that are found immediately posterior to PstA cells but anterior to 80% of 
the slug that consists of prespore cells. Half of these are also expressed 
in PstA cells.  At later stages of development the patterns of expression 
for a considerable number of these prestalk genes changes significantly 
allowing us to further subdivide them. Some are expressed at much higher 
levels during culmination while others are repressed. These results 
demonstrate the extremely dynamic nature of cell type specific expression 
in Dictyostelium and further define the changing physiology of the cell 
types.  One of the signals that affect gene expression in PstO cells is 
the hexaphenone DIF-1. We found that expression of about half of the PstO 
specific genes were affected in a mutant that is unable to synthesize 
DIF-1, while the rest appeared to be DIF- independent. These results 
indicate that differentiation of some aspects of PstO cells can occur in 
the absence of DIF-1.

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[End Dicty News, volume 20, number 3]