Biomedical Engineering Reference
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in the inverse orientation. Although initially the gene expression patterns in the anterior and
posterior parts were rather diferent, ater approximately 200 minutes, the patterns were very
similar regardless of the environmental diferences that the embryos had been exposed to (see
Figure 6.75
).
6.7 Yeast Biology
In 2005, Jef Hasty's group at the University of California (San Diego) was able to solve a critical
technical problem that had prevented researchers from studying yeast in microluidic environ-
ments: yeast are not adherent and, as they divide, grow forming multilayers that are diicult to
observe and perfuse. he Hasty group designed a cell culture chamber in the shape of a Tesla
valve (
Figure 6.76a
), which has a loop region of high-resistivity slow low (4 μm tall, just tall
enough for one yeast cell) and a bypass region of low-resistivity fast low (8 μm tall). In the loop
region, the cells are always constrained to divide in the plane of focus (laterally, see
Figure
6.76b
) and the low is so slow that they are not sheared away (see low velocity modeling in
Figure 6.76c
). Pictures of the cells dividing are shown in
Figure 6.76d
and
e
. Segmentation algo-
rithms could be applied to identify the newly divided cells (
Figure 6.76f
), so that the daughter,
granddaughter, and great-granddaughter cells of each cell could be tracked to obtain senescence
data.
he Tesla valve is not essential for achieving low low and cell trapping. he essence of the
design is that the chamber containing the cells must have a low ceiling (4 μm) to (a) produce
a high resistivity to low and (b) facilitate microscopic observation as the cells divide. Andre
Levchenko's group at Johns Hopkins University has achieved the same goals with a difer-
ent design (
Figure 6.77
) that also allows for producing gradients in the cell chambers. he
Levchenko design features 5-μm-deep cell-containing chambers perpendicularly connected to
two 25-μm-deep low-through channels (which are each fed with diferent solutions, creating a
gradient in the cell chambers); if the two low-through channels are run at the same exact pres-
sure, then the low through the cell-containing chambers should equal zero. he team has used
the design to investigate MAPK-mediated bimodal gene expression and phenotypic changes
associated with the mating response of
Saccharomyces cerevisiae
under microluidically gener-
ated pheromone gradients.
a
b
c
0
75 µm/s
v~75 µm/s
c
0
Medial flow
Central
streamline
c
0
c
0
v
y
x
= 0
x
=
L
Trapping
region
v~1.5 µm/s
x
d
e
4-µm-high
chamber
f
8 µm height
4 µm height
20 µm
FIGURE 6.76
High-throughput. studies. of. senescence. with. yeast. in. a. microluidic. environment..
(From.Scott.Cookson,.Natalie.Ostroff,.Wyming.Lee.Pang,.Dmitri.Volfson,.and.Jeff.Hasty,.“Monitoring.
dynamics.of.single-cell.gene.expression.over.multiple.cell.cycles,”.
Mol. Syst. Biol.
,.msb4100032,.
2005..Reprinted.with.permission.from.the.Nature.Publishing.Group.)
