CELL BIOLOGY OF DEVELOPMENT
Robert Saint Laboratory
Canberra +61 2 6125 2383 / Adelaide
+61 8 8303 3256
Canberra +61 2 6125 8294 / Adelaide
+ 61 8 8303 7534
In a developing embryo, cells divide, change shape, migrate, differentiate
and/or die in a highly regulated way. The aim of our research is to understand
the molecular basis of these cellular behaviours, particularly those involving
cell division, shape change and migration, all processes that rely on coordinated
regulation of the cytoskeleton. Our focus is on small G protein signalling pathways
that regulate the cytoskeleton. We use, as our model organism, Drosophila melanogaster.
The study of this animal is particularly rewarding because we have a detailed
description of the cellular basis of development and a complete genome sequence
to underpin our research. We use sophisticated molecular, genetic, cell biological
and cytological techniques, including a relatively simple means of genetic transformation,
to probe cellular and developmental roles for our genes of interest. Drosophila
research provides exciting intellectual challenges because of the powerful experimental
approaches available. Furthermore, experience shows that discoveries made in
Drosophila often lead the way by creating concepts and tools for the analysis
of cell and developmental biology in other organisms.
Collaborators & Linkages
- Dr. Francois Schweisguth, Ecole Normale Superieure. Paris, France.
- Dr. Amy Bejsovec, Cell and Molecular Biology Program, Duke University, Durham,
- Dr. Barry Dickson, Inst. of Molecular Pathology, Vienna, Austria.Assoc.
- Prof. Robert Richards, School of Molecular
and Biomedical Sciences, University of Adelaide, Adelaide SA.
- Dr. David Miller, Comparative Genomics Centre, James Cook University, Townsville,
- Prof. Christopher Goodnow and Dr. Carola Vinuesa, John Curtin School of
Medical Research, Australian National University, Canberra, ACT
- Dr. Nicholas Dixon and Dr. Aaron Oakley, Research School of Chemistry, Australian
National University, Canberra, ACT
- Dr. Carolyn Behm, School of Biochemistry and Molecular Biology, Australian
National University, Canberra, ACT
- Dr. Eldon Ball, Research School of Biological
Sciences, Australian National University, Canberra, ACT.
- ARC/NHMRC Research Network in
Genes and Environment in Development (NGED)
Rho small GTPase Signalling
in Cell division
Stephen Gregory, Hamilton Fraval, Saman Ebrahimi, Nelida Contreras and Robert
We continue to explore the role of the Rho small G protein signalling pathway
in cell division. Our discovery of an interaction between a Rho family GTP exchange
factor, Pebble (Pbl), and a Rho family GTPase activating protein, Tumbleweed
(Tum), enabled us to propose a model for the positioning of the contractile
ring during cell division. This model has formed the basis for studies in other
systems, such as mammalian cells, where it appears to hold true. Our work now
investigates the nature of the interactions between the factors involved via
structure function analysis and advanced microscopy techniques and studies of
the events that occur downstream of Pbl-Tum complex formation. Using Drosophila,
we have the advantage of being able to genetically modify the genes involved
and then study the consequences of the expression of their products in vivo.
and cell migration in Drosophila
Michael Murray, Ursula Wiedemann, Nirmal Lorensuhewa, Kate Kearney, Upulie
Divisekera, Jianbin Wang, and Robert Saint
Epithelial to mesenchymal transitions (EMT), the process by which cells disengage
from their epithelial connections and adopt a migratory mesenchymal morphology,
are an important component of embryonic development and are thought also to
occur during the metastasis of epithelial tumours. During Drosophila development
EMTs are utilised in various morphogenetic processes, such as mesoderm and endoderm
development. In mesoderm development, cells of the ventral epidermis invaginate,
undergo an EMT, and then migrate dorsally, spreading out over the underlying
epidermis to form a monolayer. Like other EMTs this process involves the activation
of an FGF Receptor/MAPK pathway. We have previously shown that the RhoGEF Pbl,
well known for its role in cell division, is required for this process. In pebble
embryos, mesodermal cells appear more tightly adhered to each other and extend
fewer protrusions and fail to migrate. To identify genes involved in the Pebble-activated
small GTPase signalling pathway operating in mesodermal cells, we have established
a cell-marker assay for the pbl migration phenotype. With this assay we can
test the ability of different genes to positively or negatively modulate migration
in pebble mutant embryos. We are using this system to analyse potential downstream
Rho signaling pathways as well as using it to help identify new genes that may
play a role.A less well-characterised EMT occurs in the earliest stages of embryonic
midgut formation. The Drosophila midgut forms from endodermal tissue, another
of the primary germ layers formed early in embryogenesis. Endodermal tissue
forms from groups of cells at both ends of the developing Drosophila embryo.
These cells undergo an EMT and migrate towards each other along a substrate
provided by the visceral mesoderm. In contrast to the mesoderm invagination,
the endodermal EMT and migration is followed by a mesenchymal to epithelial
transition (MET) to form an epithelial sheet that engulfs the yolk to form the
gut tube.. We have initiated an analysis of this important process, initially
by testing whether there is a requirement for pebble, as there is in the equivalent
mesodermal process. Interestingly, we find that pebble is not required in the
endoderm, even though Rho family GTPase activity has been implicated in these
Genetic modifiers of pbl
Lynn Jones, Ryan Herbert and Robert Saint
We are isolating and characterising genes identified in a dominant modifier
screen of a pbl loss of function phenotype. The screen has identified expected
modifiers, such as zipper, the Drosophila non-muscle myosin heavy chain, a known
component of the contractile ring. However, we have also identified a number
of unexpected genes that appear either to be cryptic cell cycle regulatory genes
revealed because of the particular nature of the phenotype used in the screen,
or appear to implicate pbl in novel regulatory processes. We are currently exploring
these processes to elucidate the novel roles of pbl.
The autoimmune regulator Roquin
induces and localizes to stress granules through its unique Roq domain
Vicki Athanasopoulos, Peter Smibert and Robert Saint in collaboration with
Christopher C Goodnow & Carola G Vinuesa (John Curtin School of Medical
Research. The Australian National University).
Roquin, a novel and highly conserved gene was recently discovered during an
ENU screen of the mouse genome for autoimmune regulators. Roquin acts within
peripheral T cells to suppress ICOS expression and the roquin M199R mutation
found in sanroque mice leads to spontaneous germinal centre formation, production
of autoantibodies and lupus pathology. Roquin encodes a protein belonging to
the RING-type ubiquitin ligase family, which is distinguished by a CCCH zinc-finger
motif found in RNA-binding proteins and a novel highly conserved "Roq"
domain. We have now shown that endogenous Roquin localizes to the cytoplasm,
and upon environmental stress is shuttled to discrete cytoplasmic inclusions
termed stress granules. Stress granules are sites of recruitment of stalled
translation initiation complexes. At these sites, decisions as to whether specific
mRNAs are degraded or allowed to proceed with translation are taken. These results
strongly suggest Roquin and MNAB are RNA binding proteins involved in regulating
mRNA metabolism and/or stability. We are now characterizing the Drosophila ortholog
of Roquin to throw light on to the molecular function of this protein.
Publications (since 2000)
Coulson, M., Robert, S., Saint, R. (2005) Drosophila starving encodes a tissue-specific
BAG domain protein required for larval food uptake . Genetics 171:1799-812
O'Keefe, L.V., Liu, Y-H., Perkins, A., Dayan, S., Saint, R., Richards, R.I.
(2005) FRA16D common chromosomal fragile site oxido-reductase (FOR/WWOX) protects
against the effects of ionising radiation in Drosophila. Oncogene 24: 6590-6.
Technau, U., Rudd, S, Maxwell, P., Gordon, P.M.K, Saina, M., Grasso, L.C., Hayward,
D.C., Sensen, C.W., Saint, R., Holstein, T.W., Ball, E.E., Miller, D.J. (2005)
Maintenanceof ancestral complexity and non-metazoan genes in two basal cnidarians.
Trends in Genetics 21: 633-9
Zavortink, M., Contreras, N., Addy, T., Bejsovec, A., Saint, R. (2005) Tum/RacGAP50C
provides a critical link between anaphase microtubules and the assembly of the
contractile ring in Drosophila melanogaster. Journal of Cell Science 118:5381-92
Ball, E.E., Hayward, D.C., Saint, R., Miller, D.J. (2004) A simple plan - cnidarians
and the origins of developmental mechanisms. Nature Reviews Genetics 5: 567-77
Brumby, A., Secombe, J., Horsfield, J., Coombe, M., Amin, N., Coates, D., Saint,
R, Richardson, H. (2004) A genetic screen for dominant modifiers of a cyclin
E hypomorphic mutation identifies novel regulators of S-phase entry in drosophila.
Genetics 168: 227-51
Shandala, T., Gregory, S.L., Dalton, H.E., Smallhorn, M., Saint, R. (2004) Citron
Kinase is an essential effector of the Pbl-activated Rho signalling pathway
in Drosophila melanogaster. Development 131: 5053-63
Smallhorn, M., Murray M.J., Saint, R. (2004) The epithelial-mesenchymal transition
of the Drosophila mesoderm requires the Rho GTP exchange factor Pebble. Development
Kortschak, R.D., Samuel, G., Saint, R., Miller, D.J. (2003) EST analysis of
the cnidarian Acropora millepora reveals extensive gene loss and rapid sequence
divergence in the model invertebrates. Current Biology 13: 2190-95
Saint R., Somers, W.G. (2003) Animal cell division: a fellowship of the double
ring? Journal of Cell Science 116: 4277-81
Shandala T., Takizawa, K., Saint, R. (2003) The dead ringer/retained transcriptional
regulatory gene is required for positioning of the longitudinal glia in the
Drosophila embryonic CNS. Development 130:1505-13
Somers, W.G. and Saint, R. (2003) A RhoGEF and Rho family GTPase-activating
protein complex links the contractile ring to cortical microtubules at the onset
of cytokinesis. Developmental Cell 4: 29-39
Ball, E.E., Hayward, D.C., Reece-Hoyes, J.S., Hislop, N.R., Samuel, G., Saint,
R., Harrison, P.L., Miller, D.J. (2002) Coral development: from classical embryology
to molecular control. International Journal of Developmental Biology 46: 671-8
Brumby, A.M., Zraly, C.B., Horsfield, J.A., Secombe, J., Saint, R., Dingwall,
A.K., Richardson, H. (2002) Drosophila cyclin E interacts with components of
the Brahma complex. EMBO Journal 21:3377-89
Crack, D., Secombe, J., Coombe, M., Brumby, A., Saint, R., Richardson, H. (2002)
Analysis of Drosophila cyclin EI and II function during development: identification
of an inhibitory zone within the morphogenetic furrow of the eye imaginal disc
that blocks the function of cyclin EI but not cyclin EII. Developmental Biology
Hayward, D.C., Samuel, G., Pontynen, P.C., Catmull, J., Saint, R., Miller, D.J.,
Ball, E.E. (2002) Localized expression of a dpp/BMP2/4 ortholog in a coral embryo.
Proceedings of the National Academy of Sciences USA 99:8106-11
Saint, R. (2002) Profile of the Adelaide Centre for the Molecular Genetics
of Development. International Journal of Developmental Biology 46: 361-2
Shandala T., Kortschak R.D., Saint R. (2002) The Drosophila retained/dead ringer
gene and ARID gene family function during development. International Journal
of Developmental Biology 46: 423-30
Wilanowski, T., Tuckfield, A., Cerruti, L., O'Connell, S., Saint, R., Parekh,
V., Tao, J., Cunningham, J.M., Jane, S.M. (2002) A highly conserved novel family
of mammalian developmental transcription factors related to Drosophila grainyhead.
Mechanisms of Development 114:37-50
Knox, R.B., Ladiges, P., Evans, B. and Saint, R. (2001) Biology (2nd Edition).
O'Connell, S., Wang, L., Robert, S., Jones, C. A., Saint, R., Jones, R. S. (2001)
Polycomblike PHD fingers mediate conserved interaction with Enhancer of zeste
protein: evidence for multiple isoforms of a Polycomb-group complex. Journal
of Biological Chemistry, 276:43065-43073
O'Keefe, L., Somers, W.G., Harley, A., Saint, R. (2001The Pebble GTP Exchange
Factor and the Control of Cytokinesis. Cell Struct. Function 26:619-26
Samuel, G., Miller, D.J., Saint, R. (2001) Conservation of a DPP/BMP signalling
pathway in the non-bilateral cnidarian, Acropora millepora. Evolution and Development.
Williams, R.T., Manji, S.S.M., Parker, N.J. Hancock, M.S., Van Stekelenburg,
L., Eid, J.-P., Senior, P.V., Kazenwadel, J.S., Shandala, T., Saint, R., Smith,
P.J. and Dziadek, M.A. (2001) Identification and characterisation of the STIM
gene family: Coding for a novel class of transmembrane proteins. Biochem. J.
Hader, T., Wainwright, D., Shandala, T., Saint, R., Taubert, H., Bronner, G.,
Jackle, H. (2000) Receptor tyrosine kinase signalling regulates different modes
of Groucho-dependent control of Dorsal. Current Biology 10 (1):51-54
Jones, L., Richardson, H., Saint, R. (2000) cyclin E transcription is regulated
by multiple tissue specific regulatory elements during Drosophila melanogaster
embryogenesis. Development, 127:4619-4630.
Kortschak, R. D., Tucker, P.W., Saint, R. (2000) ARID proteins come in from
the desert. Trends in Biochemical Sciences. 25: 294-299.
Matthies, H.J.G., Clarkson, M., Saint, R., Hawley, R.S. (2000) Analysis of meiosis
by light microscopy of fixed and live oocytes. In Drosophila: A Laboratory Manual.
Eds. Sullivan, W., Ashburner, M., Hawley, R.S. Cold Spring Harbor Press.
Prokopenko, S.N., Saint, R., Bellen, H.J. (2000) Untying the gordian knot of
cytokinesis: Role of small G proteins and their regulators. Journal of Cell
Biology. 148: 843-848.
Prokopenko, S.N., Saint, R., Bellen, H.J. (2000) Tissue distribution of Pebble
RNA and Pebble protien during Drosophila embryonic development. Mechanisms of
Saint, R., Clarkson, M. (2000) A functional marker for Drosophila chromosomes
in vivo. Trends in Cell Biology, 10:553.
Yu, K.R., Saint, R., Sullivan, W. (2000) The Grp checkpoint coordinates nuclear
envelope breakdown and chromosome condensation. Nature Cell Biology, 2:609 -