BioMEMS for Cell Biology - Introduction to BioMEMS - page 366

question regarding the second messengers responsible for the propagation of calcium waves: are
they released and difuse to neighboring cells through the extracellular luid, or do they difuse
intercellularly through the gap junctions? Figure 6.74b shows a sequence of images of astrocytes
loaded with a calcium indicator immediately ater mechanical stimulation, showing that the
calcium wave is able to spread across extracellular gaps (i.e., gap junctions are not necessary to
mediate difusion of second messengers). Communication across the lanes does not happen in
the presence of an ATP inhibitor ( Figure 6.74c ), which supports the existence of an extracellular
communication pathway via a messenger like ATP.

6.6 Developmental Biology on a Chip
During development, the embryo (initially formed from just a few cells) is constantly changing
the microenvironment of every cell by following a inely orchestrated gene expression program.
Clearly, these time-changing microenvironments cannot be accurately reproduced in tradi-
tional petri dishes. On the other hand, microluidic systems—with their ability to deliver luids
to particular locations on demand—ofer an enormous potential, mostly untapped to this day,
to investigate development in vitro. We have already seen examples in Chapter 5 of how micro-
luidics can be used to manipulate embryos for practical applications (e.g., fertilization studies).
Here we review research eforts that use microfabrication tools to address basic developmental
biology questions.
Rustem Ismagilov and colleagues at the University of Chicago have used spatial patterns
of gene expression in Drosophila to study perturbations in biochemical networks. he pertur-
bations can be compensated during development, which makes them an especially attractive
case study for probing the spatiotemporal dynamics of biochemistry on a whole-cell scale. To
that end, a Drosophila embryo was placed inside a microluidic channel that had two inputs,
one carrying a warm (27°C) solution and the other a cool (20°C) solution, which produced a
nonphysiological temperature “step” that caused diferent parts of the embryo to develop at
diferent rates. Some embryos were exposed to warm solution in the anterior part, and others

PDMS

27°C

300
299
298
297
296
295
294
293
T (K)

Warm Cool Cool

20°C

Warm

a b c z

y

Embryo

20°C

27°C

Embryo Embryo

Tape

Anterior Posterior Anterior Posterior

Patterned expression of Even-skipped gene under a T step

Warm Cool Warm Cool Warm Cool

d

180 min 190 min 200 min

Cool Warm Cool Warm Cool Warm

e

190 min 200 min 210 min

FIGURE 6.75 Patterns.of.gene.expression.in. Drosophila .embryos.microluidically.stimulated.with.a.
temperature.gradient..(From.Elena.M..Lucchetta,.Ji.Hwan.Lee,.Lydia.A..Fu,.Nipam.H..Patel,.and.
Rustem.F..Ismagilov,.“Dynamics.of.Drosophila.embryonic.patterning.network.perturbed.in.space.
and.time.using.microluidics,”. Nature .434,.1134-1138,.2005..Adapted.with.permission.from.the.
Nature.Publishing.Group..Figure.contributed.by.Rustem.Ismagilov.)