CSM News
Electronic Edition
Volume 2, number 4
January 22, 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.

Back issues of CSM-News, the CSM Reference database and other useful
information is available by anonymous ftp from worms.cmsbio.nwu.edu
[129.105.233.50], via Gopher at the same address, or by World Wide Web
through WWW.acns.nwu.edu.

=========
Abstracts
=========

dutA RNA functions as an untranslatable RNA in the development of
Dictyostelium discoideum.

Hiderou Yoshida, Hiroshi Kumimoto and Koji Okamoto
	         
Department of Botany, Faculty of Science, Kyoto University, Kyoto
606-01, Japan.  TEL: +81-75-753-4128, FAX: +81-75-753-4122

Nucleic Acids Research, in press.

   dutA is a gene specifically expressed during the development
of Dictyostelium discoideum.  Toward understanding its possible role
in development, we isolated and characterized the gene and its
complete cDNA.  We found that dutA is encoded by the nuclear genome as
a single copy gene without introns.  In addition, the following unique
and interesting features of dutA RNA (1322nt) emerged: (1) it has no
sustained ORFs (MAX=126nt) (2) it is extremely AU-rich (83%) (3) it
contains peculiar sequence motifs (large palindromes, long
AU-stretches and GC-clusters) (4) it is localized in the cytoplasm but
completely absent from ribosomes.  These features suggest that dutA
RNA functions without being translated into protein.  Disruption of
the dutA gene did not cause phenotypic changes, suggesting that the
function of dutA is redundant.

----------------------------------------------------------------------

Signal transduction during cannibalistic sexual phagocytosis: Calcium
is not the trigger.

Keith E. Lewis, Darren D. Browning and Danton H. O'Day

Cellular Signalling, in press.

   After fertilization the zygote giant cell of Dictyostelium discoideum 
chemoattracts and subsequently engulfs hundreds of amoebae of the same 
species and strains from which it was derived. A pharmacological approach 
indicates that, while it may have some role, calcium is not the trigger 
for this cannibalistic  phagocytic process. Of several agents that 
perturb intracellular calcium levels (A23187, LaCl, TMB-8, and 
chlorotetracycline), only A23187 had an effect at reducing amoebal 
ingestion. In keeping with this, agents which interfered with downstream 
effectors of calcium function did not alter sexual phagocytosis. 
Calmidazolium and trifluoperazine, which inhibit calmodulin function, 
were ineffective as were a protein kinase inhibitor (starurosporine) and 
activator (phorbol 12-myristate 13-acetate). On the other hand, the 
nucleotide analogs GTPgammaS and GDPbetaS both inhibited sexual 
phagocytosis indicating a role for GTP-binding protein activity at some 
stage in the process. Sub-fractionation of cells from non-phagocytic 
and phagocytic stage cell cultures follwoed by immunolocalization after 
SDS-PAGE and western blotting revealed a number of GTP-binding proteins 
in both the cell membrane and intracellular membrane fractions that 
might function during the events of sexual phagocytosis.     

-----------------------------------------------------------------------

Cannibalistic Sexual Phagocytosis in Dictyostelium 
discoideum is modulated by adenosine via an A2-like receptor.

Keith E. Lewis and Danton H. O'Day

Cellular Signalling, in press 

   A unique aspect of phagocytosis during the sexual cycle of
Dictyostelium discoideum is the ability of the zygote giant cell (ZGC)
to attract and engulf hundreds of amoebae of the same species. The
work presented here is one of two initial attempts to understand the
signal transduction pathways that are involved during this event. Our
data indicate that the uptake of amoebae by the ZGCs is negatively
modulated by 5'AMP and adenosine (ADO). The hierarchical inhibition of
phagocytosis by the ADO analogs, NECA and PIA, argue that the
phagocytosis of amoebae by ZGCs is mediated by an adenosine receptor
which is similar to the purinogenic class of receptor, A2. As with the
A2 receptor, stimulation of cells by ADO binding causes an
up-regulation of cAMP synthesis thereby increasing the intracellular
levels of cAMP. During the phagocytic phase of sexual development,
5'AMP and ADO undergo marked and successive increases in amounts
supporting their natural role in modulating phagocytosis. This
negative modulation of phagocytosis by ADO is similar to that found in
mammalinan macrophages and may represent an evolutionary precursor to
that regulatory process. Furthermore, the slowing of phagocytosis has
important implications to sexual development of D. discoideum.

-----------------------------------------------------------------------

[End CSM News, volume 2, number 4]