Fluorescent Proteins as Visible In Vivo Sensors - Progress in Molecular Biology and Translational Science - page 388

Abstract
Fluorescent proteins have enabled a whole new technology of visible in vivo genetic
sensors. Fluorescent proteins have revolutionized biology by enabling what was for-
merly invisible to be seen clearly. These proteins have allowed us to visualize, in real
time, important aspects of cancer in living animals, including tumor cell mobility, inva-
sion, metastasis, and angiogenesis. These multicolored proteins have allowed the color
coding of cancer cells growing and enabled the distinction of host from tumor

with single-cell resolution. Whole-body imaging with fluorescent proteins has been
shown to be a powerful technology to noninvasively follow the dynamics of metastatic
cancer. Whole-body imaging of cancer cells expressing fluorescent proteins has en-
abled the facile determination of efficacy of candidate antitumor and antimetastatic
agents in mouse models. The use of fluorescent proteins to differentially label cancer
cells in the nucleus and cytoplasm and high-powered imaging technology have
enabled the visualization of the nuclear - cytoplasmic dynamics of cancer cells in vivo,
including noninvasive techniques. Fluorescent proteins thus enable both macro- and
microimaging technology and thereby provide the basis for the new field of

in vivo

in vivo cell

biology.

1. INTRODUCTION

Our laboratory has pioneered the field of in vivo visible genetic sensors
using fluorescent proteins. 1-6 This development was enabled by the
discovery of the green fluorescent protein (GFP) by Shimomura, 7 the
discovery and purification of the red fluorescent protein (RFP) by Labas
and Savitsky, 8 and the cloning of the GFP gene by Prasher. 9

2. NONINVASIVE IMAGING
There have been many misleading papers that GFP is not usable for
in vivo imaging 10-12 because of interference by skin autofluorescence.
Apparently, these authors were not aware that very simple equipment
with a narrow-band excitation filter and a bandpass emission filter can be
used to image the whole body of mice implanted with cells expressing
fluorescent proteins, without interference from skin autofluorescence. 13
These same authors have propagated the misconceptions in the literature
suggesting fluorescent proteins are inferior to luciferase for imaging. 14-16
The results described here should greatly clarify this subject.
This chapter will demonstrate the following: (i) very strong signals are
emitted from GFP- and RFP-expressing tumors inside the animal; (ii) the