Table Of ContentCELL SIGNALLING IN PROKARYOTES AND LOWER METAZOA
CELL SIGNALLING IN
PROKARYOTES AND
LOWER METAZOA
Edited by
Ian Fairweather
School of Biology and Biochemistry
The Queen's University of Belfast
Belfast, Northern Ireland
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
Library of Congress Cataloging-in-Publication Data is available
ISBN 978-90-481-6483-7 ISBN 978-94-017-0998-9 (eBook)
DOI 10.1007/978-94-017-0998-9
Printed an acid-free paper
AII rights reserved
© 2004 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 2004
Softcover reprint of the hardcover 1s t edition 2004
No part of the material protected by this copyright may be reproduced or utilized in
any form or by any means, electronic, mechanical, including photocopying, recording
or by any information storage and retrieval system, without written permission from
the copyright owners.
CONTENTS
Preface vn
Chapter 1 1
G proteins and MAP kinase cascades in the pheromone response of
fungi
Ann Kays, and Katherine A. Borkovich
Chapter 2 27
Prokaryotic intercellular signalling - Mechanistic diversity and unified
themes
Clay Fuqua and David White
Chapter 3 73
Signal transduction mechanisms in protozoa
Fernando L. Renaud, Jose de Ondarza, Pierangelo Luporini,
Michael J. Marino, and Judy van Houten
Chapter 4 91
Signalling systems in cnidaria
Werner M iiller
Chapter 5 115
Neuropeptides in cnidarians
Cornelis J.P. Grimmelikhuijzen, Michael Williamson,
and Georg N. Hansen
Chapter 6 141
Signalling mechanisms in platyhelminths
Ian Fairweather
Chapter 7 195
Control of Caenorhabditis elegans behaviour and development by
G proteins big and small
Carol A. Bastiani, Melvin I. Simon, and Paul W. Sternberg
Chapter 8 243
Electrophysiological and pharmacological studies on excitable tissues
in nematides
Robert J. Walker, Candida M. Rogers, Christopher J. Franks,
and Lindy Holden-Dye
v
vi CONTENTS
Chapter 9 303
Evidence for an annelid neuroendocrine system
Michel Salzet, Didier Vieau, and Christophe Breton
Chapter 10 325
Ion channels of microbes
Christopher P. Palmer, Ann Batiza, Xin-Liang Zhou, Stephen H.
Loukin, Yoshiro Saimi, and Ching Kung
Chapter 11 347
Bacterial signal transduction: Two-component signal transduction as a
model for therapeutic intervention
Lenore A. Pelosi, K wasi A. Ohemeng, and John F. Barrett
Index 403
PREFACE
Cell signalling lies at the heart of many biological processes and currently is
the focus of intense research interest. In multicellular organisms, it is central
to how different types of cell communicate with each other and how they detect
and respond to extracellular changes. Intercellular communication is vital to
single-celled organisms as well, allowing them to respond to environmental
cues and signals. As a parasitologist, I became interested in cell signalling
through studies on the nervous system of flatworms and nematodes. The idea
for the book, however, stemmed from a course in Endocrinology I taught at
Queen's. It struck me that there is a perception in the academic community
that, in terms of cell signalling, invertebrates barely exist below the level of
molluscs and arthropods and that much of the understanding of signalling
mechanisms and integration of pathways has come from research on specific
cell types, such as lymphocytes and cardiomyocytes, in mammals. More simple
organisms are largely ignored. Yet there is much of interest to be learnt from
examining the ways in which the basic principles of signalling mechanisms
were laid down in unicellular organisms, then developed in different directions
as body patterns became more complex and different types of cells and tissues
needed to find new ways to communicate with each other. Separate nervous
and endocrine systems evolved, as did vascular systems, and signalling mole
cules were appropriated for new uses. The book deliberately focuses on the
early stages in the evolution of communication systems, drawing information
together in a way that has not been attempted before.
The book begins - as signalling did - with intercellular communication in
fungi, bacteria and protozoans. These organisms needed to be able to respond
to environmental signals and to be able to secrete extracellular signals (phero
mones) in order to co-ordinate their activity. The book then follows the develop
ment of the nervous system in the cnidarians, platyhelminths and nematodes
through to the annelids, where a separate endocrine system is present. This
opened up the possibility of signalling molecules being used for intercellular
communication within organisms, as neurotransmitters, neuromodulators, neu
romuscular transmitters, neurohormones and morphogens, or "hormones".
Many of the molecules are similar to those in more advanced organisms and
the evolutionary conservation of signalling molecules and pathways will be
highlighted. Nor are ion channels the sole preserve of higher organisms with
nervous systems, either, as the chapter on ion channels in microbes will demon
strate. Simple organisms have considerable value as models for studying devel
opmental processes and unravelling the underlying signalling pathways and
this will be emphasised. Many of the groups covered contain important patho
gens or parasites and the potential for manipulating signalling pathways for
vii
viii PREFACE
therapeutic intervention will be highlighted. Adaptation to a parasitic way of
life has opened up the possibility of even more complex signalling processes,
with bidirectional communication between the parasite and its host.
Consequently, while the groups covered in the book may be considered to be
relatively "simple" with regard to their morphology, they are certainly far from
simple in terms of their complement of signalling molecules and processes.
Many of the elements typical of more advanced and more widely studied
organisms are already present in lower groups, and so it is to them that one
must look for the initial, exciting steps in how cells and tissues learnt to talk
to each other.
This book should be of value to students and researchers in a wide variety
of disciplines: endocrinology, neurobiology, cell signalling, microbiology, para
sitology, veterinary science and clinical science. It will serve to put cell signalling
in a wider, evolutionary context. I hope that it will attract interest in some
groups which have been neglected in the past.
I have been particularly lucky with the authors who have contributed to the
book, not only because of their expertise, but because of the way in which their
Chapters have fitted in with the overall themes of the book. I must thank them
for their patience in what has been a long gestation period. Thanks, too, to
other academics not in the book who made many useful suggestions about
potential authors in areas outside my own. To those potential authors who
agreed to contribute to the book yet in the end failed to do so, which led to
delays in publication, I extend my disappointment. The book would have been
more balanced and the better with their Chapters. I would like to extend my
sincere gratitude to the staff at Kluwer who have kept faith with the project.
Particular appreciation goes to Esther Verdries who has done a superb job in
putting the book together. Finally to my son, Simon, whose computer knowl
edge and advice has been invaluable to me as I moulded the Chapters into a
common format.
Ian Fairweather
CHAPTER 1
G PROTEINS AND MAP KINASE CASCADES IN THE PHEROMONE
RESPONSE OF FUNGI
ANN KAYS and KATHERINE A. BORKOVICH
Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School,
Houston, Texas 77030, USA
Summary
Development in fungal systems occurs in response to environmental cues and external stimuli.
Heterotrimeric G protein coupled receptors (GPCRs) provide these systems with the ability to
receive and transmit external signals into the cell. Once the signal has been internalized, mitogen
activated protein kinase (MAPK) and/or cAMP-dependent protein kinase (PKA) cascades amplify
and integrate various stimuli. Studies of heterotrimeric G proteins in yeast and filamentous fungi
reveal remarkable evolutionary conservation in the signal transduction pathways of lower eukaryo
tic and mammalian cells. Because of the ease of genetic and biochemical manipulation, fungi have
proven to be an invaluable system for dissecting the complex regulatory networks involved in
higher eukaryotic signalling. In this chapter, we will examine cell-cell communication in fungi by
addressing the pheromone response signal transduction pathway. The similarities and differences
observed between the Saccharomyces cerevisiae and Schizosaccharomyces pombe yeast pheromone
response pathways will be used as a paradigm for discussing sexual development in the filamentous
species Cryptococcus neoformans, Magnaporthe grisea, Neurospora crassa, and Ustilago maydis.
1. Introduction
1.1. HETEROTRIMERIC G PROTEINS
Heterotrimeric G proteins are composed of a GTPase rx subunit and a ~y
dimer (Dessauer, Posner and Gilman, 1996). In the basal state, the ~y moiety
is associated with the GDP-bound Grx subunit at the cytoplasmic domains of
seven transmembrane rx helical receptors, referred to as G protein coupled
receptors (GPCRs). A variety of external stimuli, such as pheromones, hor
mones, and odourants are bound by GPCRs, resulting in the exchange of GDP
for GTP on the Grx subunit and dissociation of the Grx-GTP and ~y moiety.
Grx-GTP and the free ~y complex are then able to activate downstream effec
tors, such as enzymes and ion channels. The initiating stimulus is terminated
by hydrolysis of GTP to GDP by the Grx subunit. The otherwise slow GTPase
activity of Grx is accelerated by 'Regulators of G-protein Signalling' (RGS)
proteins (Berman and Gilman, 1998; Neer, 1997). The GDP-Grx reassociates
with ~y to await the next cycle of activation.
Grx proteins range in size from 39~52 kDa and belong to a family of GTP
I. Fairweather ( ed.), Cell Signalling in Prokaryotes and Lower Metazoa, 1-26.
© 2004 Kluwer Academic Publishers.
2 A.M KAYS AND K.A. BORKOVICH
binding proteins that includes Ras (Dessauer, Posner and Gilman, 1996). The
Gex subunit is composed of two domains, a GTPase and an ex-helical domain,
that are connected by two linkers. Most Gex subunits undergo post-translational
lipid modifications that tether the protein to the membrane (Wedegaertner,
Wilson and Bourne, 1995). The G~ subunit is approximately 36 kDa and
interacts with the Gex subunit (Dessauer, Posner and Gilman, 1996; Gautam
et al., 1998). The NH2-terminus of G~ is an amphipathic ex-helix followed by
seven repeating units of ~ 43 residues called a WD motif. Crystal structure
analysis indicates that WD motifs form seven blades that contribute to an
overall organization resembling a propeller, referred to as a ~ superbarrel. The
Gy subunit is much smaller ( 6-9 kDa) compared to the Gex and G~ proteins
and is known to undergo post-translationallipid modifications as well (Downes
and Gautam, 1999; Gautam et al., 1998). Lipid modification of Gy is not
required for interacting with G~, but functions in membrane targeting and,
therefore, facilitates complex formation with Gex. The Gy protein contacts loops
in the fifth and sixth blades of the ~ propeller and forms a coiled coil with the
G~ ex-helical domain.
G proteins have been shown to regulate adenylyl cyclase activity in many
systems, including fungi (Dessauer, Posner and Gilman, 1996; lvey, Yang and
Borkovich, 1999). Adenylyl cyclase catalyzes the production of the second
messenger cAMP from ATP. cAMP-dependent protein kinase (PKA) is an
internal cAMP receptor and is composed of two catalytic and two regulatory
subunits (Francis and Corbin, 1999). Binding of cAMP by the regulatory
subunits leads to their dissociation from the catalytic subunits. The freed
catalytic subunits phosphorylate downstream protein targets, which in many
cases include transcription factors. PKA activity is negatively regulated by
hydrolysis of cAMP to AMP by cAMP phosphodiesterase (Beavo, 1995).
1.2. MITOGEN ACTIVATED PROTEIN KINASES
Mitogen activated protein kinase (MAPK) cascades transmit signals from
extracellular stimuli to the nucleus to alter gene expression. Frequently, the
activating signal is delivered to the cascade by a Gex subunit or the G~y dimer
(Crespo et al., 1995). The structure of MAPK cascades is conserved among
eukaryotic cells and is composed of three sequentially phosphorylated proteins:
MAPK kinase kinase (MAPKKK), MAPK kinase (MAPKK), and MAPK.
Binding of a scaffolding protein to all three components of the MAPK cascade
sequesters or allows proteins to interact, maintains specificity of the cascade,
and/or monitors cellular localization (Garrington and Johnson, 1999; Widmann
et al., 1999).
The cascade is initiated by activation of MAPKKK through interacting with
heterotrimeric and/or small GTP-binding proteins or through MAPKKK
kinase phosphorylation (Crespo et al., 1994; Siow et al., 1997). Dimerization
and subcellular localization are also implicated in regulation of MAPKKK.
