2010-ASCB-Press-Book - page 10

T h e A m e r i c a n s o c i e t y f o r C e l l B i o l o g y
News from
The American Society
for Cell Biology
50th Annual Meeting
Philadelphia, PA
December 11–15, 2010
Beware the Latin tags
10:00 am, U.S. Eastern Time
Monday, December 13, 2010
Roberto Weigert
30 Convent Dr., Rm. 303A
Bethesda, MD 20892
Author presents
Monday, December 13, 2010
11:30 am–1:00 pm
Session: Exocytosis
Exhibit Halls A/B/C
Program: 1225
Board: B455
Role for the Acto–Myosin
Complex in the Dynamics of
Regulated Exocytosis Revealed
by Intravital Microscopy in
Live Rodents
A. Masedunskas, M. Sram-
kova, L. Parente, P. Amornphi-
moltham. K. Uzzun-Sales,
T.H. Bugge, R. Weigert
National Institutes of Health,
National Institute of Dental
and Craniofacial Research,
IMTU/OPCB, Bethesda, MD
This work was supported by the
Intramural Research Program
of the NIH, National Institute of
Dental and Craniofacial Research.
New intravital microscopy finds
clear differences between in vitro
and in vivo studies
he two Latin phrases pop up so
often that biologists scarcely notice
in vivo,
meaning “in life,”
in vitro,
meaning “in glass.” But an
immense difference can exist between
what goes on in cells cultured in labora-
tory glassware or those in a free-living
organism, be it a rodent, a fish, or a
person. Just how different is driven home
by discoveries made in vivo by Roberto
Weigert and colleagues at the National
Institutes of Health National Institute
of Dental and Craniofacial Research
(NIDCR), revealing inaccuracies in previ-
ous descriptions of the fundamental cell
process of exocytosis that were based on
in vitro studies. Weigert and colleagues
looked more closely at exocytosis in the
salivary glands of a living mouse through
intravital microscopy, an optical imaging
technology. What the NIDCR researchers
found in vivo was not what they expect-
ed: Exocytosis in live animals is regulated
differently from that previously observed
in cell cultures and explanted organs
used in vitro.
Exocytosis is the method by which
cells pack up secretions internally and
ferry them to the plasma membrane
(PM), which demarcates the cell from its
surroundings. There, the packages, called
secretory vesicles, fuse with the PM, eject-
ing their contents from the cell. Previous
in vitro studies in the salivary glands de-
scribed multiple secretory vesicles fusing
with the PM, forming strings of vesicles
in a process stimulated by two classes of
chemical switches called muscarinic and
-adrenergic receptors. Watching in vivo,
the NIDCR researchers saw the secretory
vesicles fuse, not in strings, but one by
one with the PM only under stimulation
-adrenergic receptors.
Further in vivo studies revealed that
the fusion step requires the assembly of
a scaffold around the membrane of the
vesicles. This scaffold contains actin, a
protein that forms filaments, and myosin
II, a protein that binds to multiple actin
filaments. When assembled, these mol-
ecules generate a contractile force, which
pushes the membranes and drives the
fusion process to completion.
These small molecular differences
could potentially have large impacts, says
Weigert. Exocytosis is fundamental to
understanding the basis of secretory dys-
functions such as diabetes, where insulin,
for example, is one of the vital substances
that the secretory vesicles carry.
These results reveal new aspects of
the regulation of exocytosis that could
not be previously appreciated by using in
vitro models, saysWeigert. It is a reminder
that glass does not always accurately re-
flect the cell biology of living animals.
Intravital microscopy using the green fluorescence protein in a live transgenic mouse (left) shows
the exocytosis of secretory granules (arrows) at the apical plasma membrane (arrowheads) of an
acinar cell in salivary glands. Confocal microscopy in mouse salivary glands expressing a plasma
membrane protein tagged with the red fluorescent protein, Tomato, shows actin (green) accumu-
lated on the surface of secretory granules fused with the plasma membrane (red) of acinar cells.
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