dictyNews
Electronic Edition
Volume 31, number 9
September 12, 2008

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Abstracts
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Dependence of Stress Resistance on a Spore Coat Heteropolysaccharide in 
Dictyostelium

Christopher M. West (1), Phuong Nguyen (1), Hanke van der Wel (1), 
Talibah Metcalf (1), Kristin R. Sweeney (2), Ira J. Blader (2), and 
Gregory W. Erdos (3) 

(1) Dept. of Biochemistry & Molecular Biology and Oklahoma Center for Medical 
Glycobiology
(2) Dept. of Microbiology and Immunology, University of Oklahoma Health 
Sciences Center, Oklahoma City, OK  73104  USA
(3) ICBR, University of Florida, Gainesville, FL  32611  USA


Eukaryotic Cell, in press

In Dictyostelium, sporulation occurs synchronously as prespore cells 
approach the apex of the aerial stalk during culmination. Each prespore cell 
becomes surrounded by its own coat comprised of a core of crystalline cellulose 
and a branched heteropolysaccharide sandwiched between heterogeneous 
cysteine-rich glycoproteins. The function of the heteropolysaccharide, which 
consists of galactose and N-acetylgalactosamine, is unknown. Two 
glycosyltransferase-like genes encoding multifunctional proteins each with 
predicted features of a heteropolysaccharide-synthase were identified in 
the D. discoideum genome. pgtB and pgtC transcripts were modestly upregulated 
during early development and pgtB was further intensely upregulated at the 
time of heteropolysaccharide accumulation. Disruption of either gene reduced 
synthase-like activity and blocked heteropolysaccharide formation, based on 
loss of cytological labeling with a lectin and absence of component sugars 
after acid hydrolysis. Cell mixing experiments showed that heteropolysaccharide 
expression is spore cell autonomous, suggesting a physical association with 
other coat molecules during assembly. Mutant coats expressed reduced levels 
of crystalline cellulose based on chemical analysis after acid degradation, 
and cellulose was heterogeneously affected based on flow cytometry and 
electron microscopy. Mutant coats also contained elevated levels of selected 
coat proteins but not others, and were sensitive to shear. Mutant spores were 
unusually susceptible to hypertonic collapse and damage by detergent or 
hypertonic stress. Thus the heteropolysaccharide is essential for spore 
integrity, which can be explained by a role in the formation of crystalline 
cellulose and regulation of the protein content of the coat. 


Submitted by: Chris West [Cwest2@ouhsc.edu]
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[End dictyNews, volume 31, number 9]