Template Matching Session |
One gene expression time series file needs to be
loaded in this mode and the content of its left most column
(gene identifiers) is displayed in the left window. The
gene expression time series used in the example
below is coming from the aphidicolin addition
synchronization experiment of Menges et al.,
2003(1)(Data). Next the expression profile of any gene of
interest can be selected as a template by simply scrolling up and
down the list of gene names in the left window. The
expression profile of the selected gene is plotted
in the middle top window in blue.
After
choosing Match! from the Match menu,
the N best matching genes together with their
fitscores will appear in the right window. Further, one can proceed by selecting any
gene from the N best matching list. Consequently, the expression profiles of the
selected gene (in red) and the template (in blue) will be visualized in the middle
window:
1) as originally positioned in time
(top panel);
2) as aligned by the DTW algorithm
(bottom panel).
The view in the middle top
window below, indicates very comparable behaviour
between the two genes. However, there is clearly a phase
shift arround time points 3 and 4. The plot
in the bottom window presents the best possible time
alignment between the two expression profiles. Note
that extra time points have appeared as a result
of the warping performed on the time
axis. These are the average values of the time points in the
alignment that have been matched against each other. For instance, time
point 4 from the blue profile has been aligned
agains time point 3 from the red profile and
consequently, new time point 3.5 has been created.
The template matching
scenario that has been demostrated above is
a rather trivial one. For more elaborated
features, as for instance data adjustment,
offset, anchor points, etc., please consult the manual (template matching
mode).
Two separate input files,
each containing a set of gene expresion time series to be
compared, are required. The files are supposed to have
the same number of profiles and the
corresponding profiles
must appear respectively in the
same order in both files. In the example below,
the time expression profiles of all CYCB genes
from the aphidicolin addition synchronization
experiment of Menges et al.,
2003(1) (Data) have been loaded into GenTχWarper and displayed in
blue. Next, the time expression profiles of all CYCB genes
from the sucrose starvation synchronization experiment of Menges et al.,
2003(1) (Data) have been
loaded and displayed in red.
The two sets of expression
profiles have been generated in different
experimental conditions and consequently, the
comparison of their absolute expression values
will not be very meaningful. Therefore before proceeding
with aligning the two sets of profiles it is
better to transform them to relative expression
values by aplying log2-transformation (Data). Then the two time series can be
aligned by simply selecting Align! in the
Align menu.
The two visualization panels provide
a comparative view of
1) the original expression
profiles (top panel);
2) their aligned with the DTW
algorithm counterparts (bottom panel).
Additionally,
GenTχWarper reports in the right window the DTW matrix
with the optimal warping path through it
indicated in red, and the final fitscore after
normalization.
The performance of the
alignment algorithm is subject to modification
via several parameters: data adjustment,
distance metric, warping window, offset and anchor
point. The usage of these is discussed in a
detail in the manual (alignment
mode).
(1)
Sakoe,H. and Chiba, S. Dynamic
programming algorithm optimization for spoken word
recognition. IEEE Trans. on Acoust., Speech,
and Signal Process., ASSP 26, 43-49
(1978).
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