Keynote Conference - Interevent

Polarizing perpendicular axes in Drosophila
Daniel St Johnston
The Gurdon Institute, University of Cambridge, UK
Almost all cells in a multicellular organism must be polarized to
perform their normal functions, while a loss of polarity is a
hallmark of cancer. Work over the last decade has revealed that
a conserved set of polarity (PAR) proteins define complementary
cortical domains in all polarized cell-types examined so far. How
these complementary domains are established is much less well
understood, however, with the exception of the C. elegans
zygote. We have analyzed how the similar PAR domains form in
the Drosophila oocyte to define the anterior–posterior axis (AP)
of the embryo. Our results reveal that the oocyte is polarized by
a different mechanism from the C. elegans zygote that also
appears to operate in epithelial cells. Nevertheless, the
organizing principles that underlie polarity seem to be
conserved.
The dorsal-ventral (DV) axis is also defined by the polarized
organization of the oocyte, in this case by the movement of the
nucleus from the posterior cortex of the oocyte to its
anterior/lateral border. Although the movement of the oocyte
nucleus was thought to depend on the prior establishment of AP
polarity, we have isolated a mutant that separates these two
processes. More importantly, live imaging reveals a novel
mechanism of nuclear movement. This reveals that the oocyte
has two parallel polarity systems and leads to a revised view of
how orthogonal AP and DV axes form.
Extrinsic influences on tumor progression - platelets and
extracellular matrix
Richard Hynes
Howard Hughes Medical Institute, Koch Institute, MIT,
Cambridge, MA 02139, USA. rohynes@mit.edu
Intrinsic changes in tumor cells contribute to metastatic
potential, but influences from the surrounding environment also
play important roles.
We have shown that platelets actively promote invasive and
malignant behavior of tumor cells by activating signal
transduction pathways (TGF- /SMAD and NF B) within the
tumor cells and enhancing invasive behavior, extravasation and
metastasis. Platelets form aggregates around tumor cells that
also recruit leukocytes, which further enhance malignancy.
Alterations in extracellular matrix (ECM) occur during normal
development and in pathologies such as fibrosis, skeletal
diseases and cancer. Despite clear indications that tumor ECM
and its interactions with cells play important roles in tumor
progression, we do not have a good picture of ECM composition,
origins and functions in tumors. One reason lies in the
biochemical properties of ECM proteins (large size, insolubility,
cross-linking, etc.) that render attempts to characterize ECM
composition very challenging.
We have developed proteomics-based methods coupled with
bioinformatic definition of the “matrisome” (ECM and ECMassociated
proteins) to analyze the protein composition of tissue
extracellular matrices. We have characterized the ECMs of
normal tissues and of non-metastatic and metastatic tumors. We
have applied this approach to understand the origins of tumor
ECM and shown that both tumor cells and stromal cells
contribute to significant changes in the ECMs of tumors of
differing metastatic potential. We have begun to apply this
approach to human patient material to characterize the ECM
composition of tumors of varying prognosis with the goal of
developing ECM signatures that may be of diagnostic and/or
prognostic value.
Navigating the cellular landscape with new optical probes,
imaging strategies and technical innovations
Jennifer Lippincott-Schwartz
Eugene Kennedy Shriver National Institute of Child Health and
Human Development, National Institutes of Health, Bethesda,
MD 20892
Emerging visualization technologies are playing an increasingly
important role in the study of numerous aspects of cell biology,
capturing processes at the level of whole organisms down to
single molecules. Recent developments in probes, techniques,
microscopes and quantification are dramatically expanding the
areas of productive imaging. Photoactivatable fluorescent
proteins (PA-FPs) have been particular fruitful in this regard.
They become bright and visible upon being exposed to a pulse of
UV light. This allows selected populations of proteins to be pulselabeled
and tracked over time. Used for in cellulo pulse chase
experiments, the PA-FPs have helped clarify mechanisms for
biogenesis, targeting, and maintenance of organelles as separate
identities within cells. PA-FPs have further permitted the
development of single molecule-based superresolution (SR)
imaging, which dramatically improves the spatial resolution of
light microscopy by over an order of magnitude (~10-20 nm
resolution). Involving the controlled activation and sampling of
sparse subsets of photoconvertible fluorescent molecules, single
molecule SR imaging offers exciting possibilities for obtaining
molecule scale information on biological events occurring at
variable time scales. Here, I discuss the new fluorescent imaging
techniques and the ways they are helping researchers navigate
through the cell to unravel long-standing biological questions.
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