CSM News
Electronic Edition
Volume 2, number 18
May 21, 1994

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to CSM-News@worms.cmsbio.nwu.edu.

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Abstracts
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The PsB Glycoprotein Complex Is Secreted as a Preassembled Precursor
of the Spore Coat in Dictyostelium discoideum.

Ned Watson, Vince McGuire and Stephen Alexander

Division of Biological Sciences University of Missouri Columbia, MO
65211

J. Cell Science, in press

SUMMARY

     The PsB glycoprotein in Dictyostelium discoideum is one of a
diverse group of developmentally regulated, prespore cell specific
proteins, which contain a common O-linked oligosaccharide.  This
post-translational modification is dependent on the wild-type modB
allele.  The PsB protein exists as part of a multiprotein complex of
six different proteins, which have different post-translational
modifications and are held together by both covalent and non-covalent
interactions (Watson et al., J. Biol. Chem., 268, 22634-22641, 1993).
In this study we have used microscopic and biochemical analyses to
examine the cellular localization and function of the PsB complex
during development.  We found that the PsB complex first accumulates
in prespore vesicles in slug cells and is secreted later during
culmination and becomes localized to both the extracellular matrix of
the apical spore mass of mature fruiting bodies and to the inner layer
of the spore coat.  The PsB associated with the spore coat is
covalently bound by disulfide bridges.  The PsB protein always exists
in a multiprotein complex, but the composition of the PsB complex
changes during secretion and spore maturation.  Some of the other PsB
complex proteins have been identified as spore coat proteins.  These
data demonstrate that some of the proteins which form the spore coat
exist as a preassembled precursor complex.  The PsB complex is
secreted in a developmentally regulated manner during the process of
spore differentiation, at which time proteins of the complex, as well
as additional spore coat proteins, become covalently associated in at
least two forms of extracellular matrix: the interspore matrix and the
spore coat.  These and other studies show that proteins with modB
dependent O-linked oligosaccharides are involved in a wide variety of
processes underlying morphogenesis in this organism.  These
developmental processes are the direct result of cellular mechanisms
regulating protein targeting, assembly and secretion, and the assembly
of specific extracellular matrices.

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[End CSM-News, volume 2, number 18]