CSM Newsletter -- Electronic Edition
Volume 1, number 2
May 22, 1993

This is the second issue of the Electronic Edition of the CSM Newsletter.
Please be sure that you contribute the abstracts of papers from your
lab as soon as the are accepted for publication.  Submit abstracts by
sending them as an e-mail message to r-chisholm@nwu.edu.  

ABSTRACTS OF RECENTLY ACCEPTED PAPERS


A repressor controls the timing and spatial localisation of stalk 
cell specific gene expression in Dictyostelium

A. J. Harwood, A. Early & J. G. Williams

Development (accepted May 11, 1993)

	The ecmA and ecmB genes of Dictyostelium encode related extracellular
matrix proteins and both are induced by DIF, the stalk cell specific 
morphogen. The ecmA gene is expressed throughout the prestalk region of the 
migrating slug but only later, at culmination, do the prestalk cells express 
the ecmB gene.  Expression of the ecmB gene is induced at the entrance to the 
stalk tube and we have identified two promoter elements that control this 
process. They act as repressors, preventing transcription in the tip of the 
migrating slug and the apical papilla of the culminant. They have a semi-
palindromic consensus sequence TTGnCAA, where n is in one case 2 and in the 
other 4. Either element alone is able to repress ecmB promoter activity in 
prestalk cells. Introduction of a single repressor element into the promoter 
of the ecmA gene changes its expression pattern to resemble that of the
ecmB gene. 

	Mutant elements, where n is altered, cause repression during the slug 
stage but allow premature ecmB expression during culmination; suggesting that 
the effective strength of the inductive signal may increase during culmination.
 Inhibition of cAMP-dependent protein kinase (PKA) in prestalk cells blocks 
both stalk cell maturation and ecmB gene expression. We show that the block to
 gene expression correlates precisely with the presence of a functional 
repressor element, supporting the notion that expression of the ecmB gene is 
controlled by a PKA dependent release from transcriptional repression. 

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Kathleen V. Nolta, Harish Padh and Theodore L. Steck

An Immunocytochemical Analysis of the Vacuolar Proton Pump in
Dictyostelium discoideum

Journal of Cell Sciences, in press

Abstract:	

     Antisera were generated in rabbits against the vacuolar proton
pump (V-H+ATPase) purified from Dictyostelium discoideum. The antisera
inhibited V-H+ATPase but not F1-ATPase activity and immunoprecipitated and
immunoblotted only the polypeptide subunits of the V-H+ATPase from cell
homogenates. Immunocytochemical analysis of intact cells and subcellular
fractions showed that the predominant immunoreactive organelles were clusters
of empty, irregular vacuoles of varied size and shape which corresponded to
the acidosomes. The cytoplasmic surfaces of lysosomes, phagosomes and the
tubular spongiome of the contractile vacuoles also bore pump antigens.  The
lumens of multivesicular bodies were often stained intensely; The internalized
antigen may have been derived from acidosomes by autophagy. Antibodies against
V-H+ATPase from plant and animal cells cross-reacted with proton pumps of
Dictyostelium. 
	Antisera directed against V-H+ATPase of Dictyostelium decorated a
profusion of small vacuoles scattered throughout the cytoplasm of hepatocytes,
epithelial cells, macrophages, and fibroblasts. The pattern paralleled that of
the endocytic and acidic spaces; there was no clear indication of discrete
acidosomes in these mammalian cells. 
	We conclude that the V-H+ATPase in Dictyostelium is distributed among
diverse endomembrane organelles and is immunologically cross-reactive with the
proton pumps on endocytic vacuoles in mammalian cells.

[END CSM Newsletter Electronic Edition Vol. 1, #2.]