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Integrating biological knowledge based on functional annotations for biclustering of gene expression data

Abstract

Gene expression data analysis is based on the assumption that co-expressed genes imply co-regulated genes. This assumption is being reformulated because the co-expression of a group of genes may be the result of an independent activation with respect to the same experimental condition and not due to the same regulatory regime. For this reason, tradi tional techniques are recently being improved with the use of prior biological knowledge from open-access repositories together with gene expression data. Biclustering is an unsupervised machine learning technique that searches patterns in gene expression data matrices. A scatter search-based biclustering algorithm thatintegrates biological information is proposed in this paper. In addition to the gene expression data matrix, the input of the algorithm is only a direct annotation file that relates each gene to a set of terms from a biological repository where genes are annotated. Two different biolog ical measures, FracGO and SimNTO, are proposed to integrate this information by means of its addition to-be-optimized fitness function in the scatter search scheme. The measure FracGO is based on the biological enrichment and SimNTO is based on the overlapping among GO annotations of pairs of genes. Experimental results evaluate the proposed algo rithm for two datasets and show the algorithm performs better when biological knowledge is integrated. Moreover, the analysis and comparison between the two different biological measures is presented and it is concluded that the differences depend on both the data source and how the annotation file has been built in the case GO is used. It is also shown that the proposed algorithm obtains a greater number of enriched biclusters than other classical biclustering algorithms typically used as benchmark and an analysis of the over lapping among biclusters reveals that the biclusters obtained present a low overlapping. The proposed methodology is a general-purpose algorithm which allows the integration of biological information from several sources and can be extended to other biclustering algorithms based on the optimization of a merit function.

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Integrating biological knowledge based on functional annotations for biclustering of gene expression data

Author: Nepomuceno Chamorro, Juan Antonio; Troncoso Lora, Alicia; Nepomuceno Chamorro, Isabel de los Ángeles; Aguilar Ruiz, Jesús Salvador
Publisher: Elsevier
Year: 2015
DOI: 10.1016/j.cmpb.2015.02.010
Source: https://idus.us.es/bitstreams/0dd8c718-fc4a-42b7-be78-d890c9b0b189/download
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jo
u
nal
ho
me
p
ag
e:
www.in l.else ie heal
h.com/jou nals/cmpb
In eg a ing
biological
knowledge
based
on
unc ional
anno a ions
o
biclus e ing
o
gene
exp ession
da a
Juan
A.
Nepomucenoa,∗,
Alicia
T oncosob,
Isabel
A.
Nepomuceno-Chamo oa,
Jesús
S.
Aguila -Ruizb
aDepa amen o
de
Lenguajes
y
Sis emas
In o má icos,
Uni e sidad
de
Se illa,
A d.
Reina
Me cedes
s/n,
41012
Se ille,
Spain
bDepa men
o
Compu e
Enginee ing,
Pablo
de
Ola ide
Uni e si y,
C a.
U e a
km.
1,
41013
Se ille,
Spain
a
i
c
l
e
i
n
o
A icle
his o y:
Recei ed
22
July
2014
Recei ed
in
e ised
o m
17
Feb ua y
2015
Accep ed
27
Feb ua y
2015
Keywo ds:
Biclus e ing
o
gene
exp ession
da a
In eg a ion
o
biological
knowledge
Sca e
sea ch
a
b
s
a
c
Gene
exp ession
da a
analysis
is
based
on
he
assump ion
ha
co-exp essed
genes
imply
co- egula ed
genes.
This
assump ion
is
being
e o mula ed
because
he
co-exp ession
o
a
g oup
o
genes
may
be
he
esul
o
an
independen
ac i a ion
wi h
espec
o
he
same
expe imen al
condi ion
and
no
due
o
he
same
egula o y
egime.
Fo
his
eason,
adi-
ional
echniques
a e
ecen ly
being
imp o ed
wi h
he
use
o
p io
biological
knowledge
om
open-access
eposi o ies
oge he
wi h
gene
exp ession
da a.
Biclus e ing
is
an
unsupe ised
machine
lea ning
echnique
ha
sea ches
pa e ns
in
gene
exp ession
da a
ma ices.
A
sca e
sea ch-based
biclus e ing
algo i hm
ha
in eg a es
biological
in o ma ion
is
p oposed
in
his
pape .
In
addi ion
o
he
gene
exp ession
da a
ma ix,
he
inpu
o
he
algo i hm
is
only
a
di ec
anno a ion
file
ha
ela es
each
gene
o
a
se
o
e ms
om
a
biological
eposi o y
whe e
genes
a e
anno a ed.
Two
di e en
biolog-
ical
measu es,
F acGO
and
SimNTO,
a e
p oposed
o
in eg a e
his
in o ma ion
by
means
o
i s
addi ion
o-be-op imized
fi ness
unc ion
in
he
sca e
sea ch
scheme.
The
measu e
F acGO
is
based
on
he
biological
en ichmen
and
SimNTO
is
based
on
he
o e lapping
among
GO
anno a ions
o
pai s
o
genes.
Expe imen al
esul s
e alua e
he
p oposed
algo-
i hm
o
wo
da ase s
and
show
he
algo i hm
pe o ms
be e
when
biological
knowledge
is
in eg a ed.
Mo eo e ,
he
analysis
and
compa ison
be ween
he
wo
di e en
biological
measu es
is
p esen ed
and
i
is
concluded
ha
he
di e ences
depend
on
bo h
he
da a
sou ce
and
how
he
anno a ion
file
has
been
buil
in
he
case
GO
is
used.
I
is
also
shown
ha
he
p oposed
algo i hm
ob ains
a
g ea e
numbe
o
en iched
biclus e s
han
o he
classical
biclus e ing
algo i hms
ypically
used
as
benchma k
and
an
analysis
o
he
o e -
lapping
among
biclus e s
e eals
ha
he
biclus e s
ob ained
p esen
a
low
o e lapping.
The
p oposed
me hodology
is
a
gene al-pu pose
algo i hm
which
allows
he
in eg a ion
o
biological
in o ma ion
om
se e al
sou ces
and
can
be
ex ended
o
o he
biclus e ing
algo i hms
based
on
he
op imiza ion
o
a
me i
unc ion.
©
2015
Else ie
I eland
L d.
All
igh s
ese ed.
∗Co esponding
au ho .
Tel.:
+34
954559769.
E-mail
add ess:
[email p o ec ed]
(J.A.
Nepomuceno).
h p://dx.doi.o g/10.1016/j.cmpb.2015.02.010
0169-2607/©
2015
Else ie
I eland
L d.
All
igh s
ese ed.
164
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1.
In oduc ion
Gene
exp ession
da a
ma ices
show
he
exp ession
p ofile
o
housands
o
genes
along
dozens
o
samples,
which
a e
s ud-
ied
in
di e en
mic oa ay
expe imen s.
Each
alue
in
hese
ma ices
is
a
nume ical
alue
ha
ep esen s
he
exp ession
alue
o
a
gene
in
a
specific
sample.
I
is
assumed
ha
g oups
o
genes
ha
sha e
a
simila
exp ession
p ofile
also
sha e
he
same
egula o y
egime
and
hence
he
same
unc ionali ies.
This
assump ion
is
called
he
guil -by-associa ion
heu is ic
[1].
I
is
la ely
being
e o mula ed
because
o
he
co-exp ession
o
a
g oup
o
genes
may
be
he
esul
o
an
independen
ac i a-
ion
wi h
espec
o
he
same
expe imen al
condi ion
and
no
due
o
he
same
egula o y
egime
is
cap u ed.
Biclus e ing
o
gene
exp ession
da a
is
an
unsupe ised
machine
lea n-
ing
echnique
ha
sea ches
g oups
o
genes
wi h
a
simila
exp ession
p ofile
unde
a
subse
o
condi ions.
Recen ly,
in e-
g a ion
me hods
based
on
he
combina ion
o
mul iple
sou ces
om
open-access
da a
ha e
been
p oposed
in
o he
fields
as
clus e ing
o
classifica ion.
These
app oaches
can
ou pe o m
he
adi ional
algo i hms
and
inc ease
he
possibili ies
o
co -
ec ing
he
spu ious
in o ma ion
exis ing
in
high- h oughpu
echnology
da a
as
gene
exp ession
da a
o
o he
“omic”
da a.
The
mos
impo an
di e ence
o
biclus e ing
wi h
espec
o
adi ional
clus e ing
is
ha
biclus e ing
aims
o
clus e
simul aneously
genes
as
well
as
condi ions,
a he
han
ocus-
ing
solely
on
ei he
one.
Clus e ing
echniques
spli
he
da a
ma ix
in o
g oups
o
co-exp essed
genes
along
all
samples
in
he
ma ix
such
ha
he
union
o
all
he
clus e s
cons i u es
he
comple e
ma ix
and
all
o
hem
a e
disjoin .
Howe e ,
biclus e ing
finds
co-exp essed
genes
only
unde
a
subse
o
samples.
The e o e,
he
o e lapping
among
esul s
is
consid-
e ed
and
he
mo i a ion
is
o
disco e
hidden
pa e ns
mo e
han
o
desc ibe
he
gene
exp ession
ma ix.
No e
ha
some
ecen ly
published
adi ional
clus e ing
algo i hms
allow
he
o e lapping
be ween
clus e s
[2,3].
The
goal
o
biclus e ing
is
o
sea ch
g oups
o
locally
co-exp essed
genes
mo e
han
o
desc ibe
he
gene
exp ession
ma ix.
The
mo i a ion
is
o
find
hidden
pa e ns
o
disco e
po en ial
bioma ke s
o
o mu-
la e
new
hypo hesis.
Al hough
biclus e ing
was
s udied
fi s ly
in
he
1960s
[4]
when
i
was
p o ed
o
be
a
NP-ha d
p oblem,
in
he
con ex
o
gene
exp ession
da a
i
was
fi s ly
in oduced
by
Cheng
and
Chu ch
[5].
In
he
con ex
o
biclus e ing,
public
da abases
and
eposi-
o ies
such
as
he
Gene
On ology
p ojec
(GO)
o
Kyo o
Encyclopedia
o
Genes
and
Genomes
(KEGG)
ha e
been
commonly
used
o
alida e
he
quali y
o
biclus e s
om
a
biological
poin
o
iew.
Conc e ely,
he
en ichmen
analysis
o
a
se
o
genes
in
he
con ex
o
GO
is
usually
used
as
a
s anda d
amewo k
o
compa ison
among
biclus e ing
algo i hms
[6].
The
esul s
a e
compa ed
acco ding
o
a
anking
based
on
he
cha ac e -
iza ion
o
each
g oup
o
genes
belonging
o
a
biclus e
wi h
espec
he
in o ma ion
s o ed
in
GO.
GO
is
an
on ology
wi h
a
hie a chical
s uc u e
wi h
h ee
oo s
o
domains:
molecu-
la
unc ion,
biological
p ocess
and
cellula
componen .
Each
gene
is
ela ed
o
a
se
o
GO
anno a ions
wi h
di e en
le -
els
o
specifici y.
These
anno a ions
a e
e ms
in
he
on ology
which
a e
linked
wi h
g oups
o
genes.
These
genes
a e
anno-
a ed
in
he
e m.
Low-le el
e ms
in
he
ee
s uc u e
epo
mo e
de ailed
in o ma ion
han
high-le el
e ms
which
a e
mo e
gene al.
Func ional
anno a ion
files
a e
buil
such
ha
each
gene
is
associa ed
wi h
he
se
o
e ms
whe e
i
is
anno-
a ed.
These
open-access
biological
da a
a e
commonly
used
in
biclus e ing
li e a u e
o
alida e
esul s
and
hei
use
is
a
common
ac o
in
mos
o
he
pape s.
Many
biclus e -
ing
algo i hms
ha e
been
p oposed
using
di e en
heu is ic
s a egies
o
sea ch
c i e ia
o
find
biclus e s
[7–9].
Se e al
algo i hms
such
as
Cheng
and
Chu ch’s
algo i hm
(CC)
[5],
I e a i e
Signa u e
Algo i hm
(ISA)
[10],
O de -p ese ing
Sub-
ma ix
Algo i hm
(OPSM)
[11]
o
xMo i s
[12]
a e
usually
used
as
benchma k
algo i hms
in
o de
o
es ablish
a
compa ison
among
biclus e ing
algo i hms.
CC
was
he
ounda ional
algo-
i hm
and
i
is
based
on
a
de e minis ic
g eedy
i e a i e
sea ch
me hod.
This
me hod
finds
biclus e s
wi h
a
esidue
less
o
equal
han
a
h eshold
ha
is
gi en
as
an
inpu
pa ame e .
Al hough
he
esidue
is
a
measu e
usually
used
in
biclus e -
ing
[5],
i
canno
cap u e
cohe en
e olu ion
pa e ns
[13].
The
ISA
algo i hm
uses
a
nonde e minis ic
g eedy
algo i hm
ha
finds
up-
and
down- egula ed
pa e ns.
The
inpu
ma ix
is
eo de ed
o
find
blocks
o
cohe en
alues
wi h
espec
o
ows
and
columns
ha
a e
epo ed
as
biclus e s.
The
OPSM
algo i hm
sea ches
o
biclus e s
acco ding
o
a
model
based
on
linea
o de ing
among
ows.
This
algo i hm
sequen ially
finds
each
biclus e
and
al hough
cohe en
e olu ion
pa e ns
a e
cap u ed,
i
canno
find
in e se
cohe en
e olu ion
pa -
e ns.
The
xMo i s
algo i hm
i e a i ely
sea ches
he
la ges
biclus e
acco ding
o
some
cons ain s
by
emo ing
samples.
Di ec
and
in e se
cohe en
e olu ion
pa e ns
a e
cap u ed
by
his
algo i hm
and
a
huge
numbe
o
biclus e s
a e
usu-
ally
epo ed.
Mo eo e ,
i
is
impo an
o
highligh
he
amily
o
biclus e ing
algo i hms
based
on
e olu iona y
compu a ion
and
me aheu is ics
ha
op imize
a
ce ain
quali y
measu e
[14–17].
Likewise,
algo i hms
o
his
amily
ha
use
measu es
based
on
co ela ions
among
genes
as
a
mechanism
o
find
co-
exp essed
genes
ha e
been
ecen ly
published
in
li e a u es
[18–26].
All
he
abo e-men ioned
algo i hms
sea ch
biclus e s
com-
posed
o
co-exp essed
genes
and
he
biological
knowledge
is
only
used
as
a
pos e io i
c i e ion
o
de e mine
he
ele ance
o
he
biclus e s
ound.
Howe e ,
he
au ho
in
[27]
conside ed
ha
he
s udies
based
on
gene
exp ession
da a
had
some
lim-
i a ions.
In
pa icula ,
he
co-exp ession
o
a
g oup
o
genes
may
be
he
esul
o
a
pa allel
and
independen
ac i a ion
wi h
espec
o
he
same
expe imen al
condi ion
and
no
due
o
cap u e
he
same
biological
unc ionali y.
The e o e,
he
assump ion
ha
co-exp ession
means
co- egula ion
should
be
ein e p e ed.
Fo
his
eason,
he
biological
knowledge
has
been
inco po a ed
du ing
he
sea ch
p ocess
o
a oid
g oups
o
co-exp essed
genes
ha
do
no
show
biologically
ep esen-
a i e
connec ions.
Fo
example
in
he
field
o
clus e ing,
he
algo i hm
p esen ed
in
[28]
uses
he
K-means
algo i hm
and
in eg a es
gene
anno a ion
files
ex ac ed
om
GO
wi h
a
con-
cep
o
dis ance
based
on
he
co-exp ession
and
unc ional
simila i y.
A
GO-based
measu e
has
been
also
applied
as
pa
o
he
wo kflow
o
a
p edic i e
algo i hm
o
classi y
genes
in
[29].
Namely,
he
a e age
o
he
Pea son
co ela ion,
which
e alua es
simila i ies
among
gene
exp ession
p ofiles,
and
a
GO-based
measu e
a e
used
o
define
a
dis ance.
This
dis ance
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
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m
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165
is
used
o
clus e
genes
and
o
elabo a e
a
anking
o
candida e
genes.
A
gene
ea u e
selec ion
me hod
is
p esen ed
in
[30]
which
in eg a es
in o ma ion
om
KEGG
ins ead
o
om
GO.
This
algo i hm
is
a
KEGG-imp o ed
e olu iona y
s a egy
ha
shows
a
be e
pe o mance
o
selec ing
genes
han
classical
algo i hms.
Func ional
simila i y
measu es
based
on
GO
in ol e
a
concep
o
dis ance
be ween
wo
genes.
The e
a e
se e al
seman ic
simila i y
measu es
o
compa e
GO
e ms
o
which
genes
a e
anno a ed
[31].
They
can
be
basically
classified
in
wo
g oups:
edge-based
measu es
and
in o ma ion
con en
(IC)-based
measu es.
The
fi s
g oup
o
measu es
assumes
ha
he
specifici y
o
a
e m
can
be
di ec ly
in e ed
om
i s
dep h
in
he
GO
g aph
and
he
second
g oup
is
based
on
he
equency
o
a
e m
in
he
GO
g aph.
Howe e ,
a
gene
is
usually
anno a ed
in
se e al
e ms
and
no
in
only
one,
and
hence,
i
is
be e
o
use
simila i y
measu es
ha
compa e
se s
o
e ms
a he
han
single
e ms.
A
compa ison
among
his
kind
o
measu es
is
p esen ed
in
[31]
whe e
he
simGIC
measu e
shows
he
bes
pe o mance.
This
measu e
compu es
he
simila i y
be ween
wo
genes
using
he
IC
associa ed
o
each
e m
in
he
genes.
No e
ha
he
GO
g aph
s uc u e
is
needed
o
compu e
he
IC
in
addi ion
o
he
gene
anno a ion
file.
Also
he e
a e
o he
measu es
based
on
a
p ep ocessed
bina y
ma ix
ins ead
o
he
ee
s uc u e
o
GO.
This
ma ix
is
composed
o
genes
as
ows
and
GO
e ms
as
columns
and
he
elemen s
a e
1
o
0
depending
on
i
he
gene
is
o
is
no
anno a ed
in
he
GO
e m,
espec i ely.
These
measu es
a e
based
on
he
Vec o
Space
Model
(VSM)
o iginally
de eloped
in
he
con ex
o
in o ma ion
e ie al.
The
measu e
p esen ed
in
[32]
can
be
also
classified
as
a
seman ic
simila i y
measu e
bu
nei he
a
p ep ocessed
ma ix
no
he
GO
g aph
s uc u e
a e
necessa y.
This
measu e
is
based
on
he
o e lapping
among
gene
anno a ions
om
fla
GO
anno a ion
files
whe e
he
ee
s uc u e
o
GO
is
cap u ed.
In
pa icula ,
he
anno a ions
o
each
gene
a e
p opaga ed
o
uppe
le els
in
he
on ology
and
all
he
associa ed
pa en
e ms
a e
conside ed.
I
can
be
s ayed
ha
he
in eg a ion
o
biological
in o ma-
ion
om
di e en
sou ces
is
ac ually
one
o
he
challenges
and
esea ch
di ec ions
in
Bioin o ma ics
[33].
The e
a e
many
wo ks
ha
use
o he
da a
sou ces,
no
only
in o ma ion
om
GO
o
KEGG.
Fo
example,
se e al
da a
sou ces
can
be
me ged
o
in eg a e
biological
knowledge
as
p o ein–p o ein
in e ac-
ion
ne wo ks,
genome-wide
binding
da a
and
in o ma ion
om
he
li e a u e
and
no
only
in o ma ion
om
GO
[34].
The
COALESCE
algo i hm
[35]
uses
he
gene
exp ession
da a
oge he
wi h
DNA
sequence
da a
as
inpu
da a
and
o he
suppo ing
da a
as
addi ional
in o ma ion
du ing
he
p o-
cess
in
o de
o
disco e
egula o y
modules.
This
algo i hm
finds
biclus e s
ha
a e
used
as
a
guide
o
disco e
hese
modules.
The
p oposed
algo i hm
in
[36]
uses
p o ein–p o ein
in e ac ion
ne wo ks
and
gene
exp ession
da a
o
disco e
cance
bioma ke s,
which
a e
ound
h ough
he
disco e ing
o
g oups
o
genes
in
biclus e s
ha
a e
also
highly
connec ed
in
he
ne wo k.
Recen ly,
a
biclus e ing
algo i hm
[37],
which
wo ks
wi h
mic oRNA
and
a ge
genes
da a,
uses
GO
in o -
ma ion
o
do
a
anking
o
he
esul s.
F om
he
bes
o
ou
knowledge,
he
biological
in o ma-
ion
in eg a ion
in
biclus e ing
o
gene
exp ession
da a
has
no
been
s ill
in es iga ed.
The
aim
o
his
pape
is
o
in oduce
his
idea
in
he
biclus e ing
field
by
means
o
unc ional
anno-
a ion
files.
These
files
a e
fla
files
whe e
each
gene
is
linked
wi h
i s
co esponding
e ms
in
he
biological
eposi o y.
The
p oposed
algo i hm
is
a
sca e
sea ch-based
me aheu is ic
ha
op imizes
a
fi ness
unc ion
which
defines
a
c i e ion
o
e alua e
he
quali y
o
he
biclus e s.
This
algo i hm
is
based
on
he
algo i hm
p esen ed
in
[25]
and
al hough
se -
e al
p ocedu es
di e ,
he
mos
ele an
con ibu ion
is
he
fi ness
unc ion
defini ion
o
in eg a e
he
biological
in o -
ma ion.
This
unc ion
consis s
o
h ee
pa s:
he
fi s
one
is
a
e m
o
con ol
he
size
o
he
biclus e s;
he
second
one
is
he
co ela ion
among
genes
o
cap u e
co-exp essed
genes;
finally,
he
hi d
e m
is
an
addi ional
e m
o
in eg a e
he
biological
in o ma ion.
The
goal
is
o
es ablish
an
equi-
lib ium
in
he
fi ness
unc ion
o
find
biclus e s
composed
o
co-exp essed
genes
ha
cap u e
simila
biological
unc-
ionali ies.
Addi ionally,
wo
di e en
biological
in eg a ion
possibili ies
a e
expe imen ally
s udied:
fi s ly,
he
biological
in o ma ion
is
included
wi h
a
measu e
p oposed
he e
based
on
an
en ichmen
s udy
o
a
se
o
genes,
and
secondly,
wi h
a
GO-based
measu e
ha
compu es
he
o e lapping
among
he
anno a ed
e ms
o
a
g oup
o
genes.
Bo h
measu es
only
use
as
inpu
da a
o
in eg a e
he
unc ional
in o ma ion
an
anno-
a ion
file
ha
ela es
genes
and
biological
e ms.
The e o e,
he
inpu
da a
o
he
algo i hm
a e
only
he
gene
exp es-
sion
ma ix
and
a
unc ional
anno a ion
file.
The
p oposed
me hodology
is
a
gene al-pu pose
algo i hm
which
allows
he
in eg a ion
o
biological
in o ma ion
om
se e al
sou ces
such
as
GO,
pa hways
KEGG
o
any
biological
in o ma ion
p o-
ided
by
fla
anno a ion
files
and
can
be
ex ended
o
o he
biclus e ing
algo i hms
based
on
he
op imiza ion
o
a
me i
unc ion.
The
emainde
o
his
pape
is
o ganized
as
ollows.
Sec-
ion
2
p esen s
he
algo i hm
whe e
fi s ly
he
fi ness
unc ion
is
defined
and
secondly
he
sea ch
p ocedu e
is
desc ibed.
In
he
fi ness
unc ion
sec ion,
wo
di e en
biological
in e-
g a ion
measu es
a e
also
defined.
Expe imen s
a e
desc ibed
and
discussed
in
Sec ion
3.
Namely,
he
expe imen al
esul s
a e
analyzed
om
h ee
poin s
o
iew:
he
in eg a ion
o
biological
in o ma ion
imp o es
he
algo i hm
pe o mance;
he
pe o mance
o
ou
app oach
is
be e
han
ha
ob ained
by
se e al
benchma k
algo i hms;
and
he
esul s
om
he
wo
di e en
biological
in eg a ion
measu es
a e
dis-
cussed.
Finally,
Sec ion
4
is
de o ed
o
conclusions
and
u u e
wo k.
2.
Me hodology
The
p oposed
me hodology
is
di ided
in o
wo
phases
clea ly
di e en ia ed.
In
a
fi s
s ep,
a
fi ness
unc ion
in eg a ing
bio-
logical
knowledge
om
unc ional
anno a ion
files
is
designed
o
measu e
he
quali y
o
biclus e s
in
Sec ion
2.2.
A
sea ch
p ocess
based
on
a
sca e
sea ch
algo i hm
is
applied
by
minimizing
he
measu e
p o ided
by
his
fi ness
unc ion
in
Sec ion
2.3.
In
a
sense,
he
me hodology
sepa a es
he
sea ch-
ing
and
he
cha ac e iza ion
o
he
biclus e s
o
be
ound.
Tha
is,
he
sea ch
p ocess
is
independen
o
he
es ablished
c i e-
ion,
which
is
defined
by
he
fi ness
unc ion,
o
find
biclus e s.
166
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
2.1.
Inpu
da a
The
inpu
da a
o
he
algo i hm
a e
basically
he
gene
exp es-
sion
ma ix
and
a
di ec
anno a ion
file.
The
gene
exp ession
ma ix
is
composed
o
gene
exp ession
p ofiles
and
samples
ha
a e
ep esen ed
in
ows
and
columns,
espec i ely.
Each
elemen
in
he
ma ix
ep esen s
he
le el
o
exp ession
o
a
gene
unde
a
pa icula
sample
o
expe imen al
condi ion.
Di ec
anno a ion
files
a e
fla
files
whe e
each
line
is
cons i-
u ed
by
a
gene
wi h
a
se
o
e ms
om
a
biological
eposi o y.
These
e ms
a e
labels
o
a
de e mined
biological
unc ion-
ali y
whe e
he
gene
is
in ol ed.
Fo
example,
his
sen ence
TVP15
GO:0006810,GO:0016192
is
a
line
in
a
di ec
anno a ion
file
ex ac ed
om
GO,
whe e
TVP15
is
he
gene
name
and
GO:0006810
and
GO:0016192
a e
wo
GO
e ms
whe e
his
gene
is
anno a ed.
No e
ha
di ec
anno a ion
files
may
be
down-
loaded
om
eposi o ies
in
se e al
ways.
Ne e heless,
he
p oposed
me hodology
is
a
gene al-pu pose
algo i hm
which
allows
he
in eg a ion
o
biological
in o ma ion
om
se e al
sou ces
o
in o ma ion.
Addi ionally,
he
numbe
o
biclus e s
o
ob ain
is
also
p o ided
as
an
inpu
pa ame e .
2.2.
Fi ness
unc ion
The
main
goal
is
o
define
a
fi ness
unc ion
ha
in eg a es
biological
knowledge
o
find
biologically
ele an
biclus e s,
in
addi ion
o
o he
measu es
such
as
he
co ela ion
o
find
biclus e s
wi h
enclosed
in e es ing
pa e ns
and
he
olume
o
find
non- i ial
biclus e s.
The
gene
exp ession
ma ix
can
be
seen
as
a
nume ical
ma ix
D
whe e
an
elemen
(i,
j)
is
he
exp ession
le el
o
gene
i
unde
he
sample
o
condi ion
j.
A
biclus e
B
is
a
subma ix
o
D
wi h
N
genes
and
M
condi ions,
ha
is,
B
=
{(gi,
cj)}i,j whe e
i
∈
{1,
.
.
.,
N}
and
j
∈
{1,
.
.
.,
M}.
The
p oposed
fi ness
unc ion
o
e alua e
B
is
defined
as
ollows:
(B)
=
M1·
1(B)
+
M2·
2(B)
+
M3·
3(B)
(1)
whe e
1measu es
he
olume
o
he
biclus e ,
2 he
pa e ns
ound
in
he
biclus e
and
3 he
quali y
o
he
biclus e
om
a
biological
iew
poin ,
and
M1,
M2and
M3a e
pa ame e s
o
weigh
he
ele ance
o
he
measu es
1,
2and
3,
espec i ely.
The
measu e
1is
used
o
con ol
he
olume
o
biclus e .
I
is
defined
as
1(B)
=1
N
·
Q(2)
whe e
N
is
he
numbe
o
genes
and
Q
he
numbe
o
condi-
ions
in
he
biclus e
B.
This
e m
is
impo an
o
deal
wi h
he
size
o
biclus e s
du ing
he
sea ch
p ocess
and
o
a oid
i ele an
in o ma ion
[38].
I
is
used
o
a oid
finding
i ial
biclus e s
wi h
only
a
e y
low
numbe
o
genes
o
condi ions,
as
o
example
a
biclus e
wi h
only
wo
condi ions.
The
measu e
2is
based
on
he
a e age
co ela ion
among
he
genes
o
he
biclus e .
No e
ha
only
he
condi ions
in
he
biclus e
a e
conside ed
and
no
all
condi ions
in
he
gene
exp ession
ma ix.
This
e m
is
conside ed
in
o de
o
cap u e
mos
o
he
ele an
pa e ns
in
biclus e s
such
as
shi ing
and
scaling
pa e ns
[13]
o
ac i a ion-inhibi ion
pa e ns
[22].
The
co ela ion
has
been
p e iously
used
as
me i
unc ion
o
de e mine
co-exp essed
genes
and
i
e alua es
he
g ade
o
dependence
among
genes
[25].
I
is
defined
as
ollows:
co (B)
=1
N
2
N−1

i=1
N

j=i+1
|ij|
(3)
whe e
ij is
he
Pea son
co ela ion
coe ficien
be ween
he
genes
giand
gj.
No e
ha
only N
2elemen s
ha e
been
con-
empla ed
due
o
he
symme y
o
he
co ela ion
coe ficien .
The
absolu e
alue
is
conside ed
o
a oid
ha
g oups
o
genes
wi h
high
posi i e
co ela ion
alues
could
elimina e
he
e ec
o
g oups
o
genes
wi h
high
nega i e
co ela ion
alues.
I
is
no ewo hy
o
men ion,
he
a e age
co ela ion
e alua es
a
biclus e
conside ing
bo h
genes
and
condi ions,
ha
is,
wo
biclus e s
wi h
he
same
se
o
genes
bu
a
di e en
se
o
condi ions
p o ide
di e en
alues
o
he
co ela ion.
As
he
sca e
sea ch
is
applied
o
minimize
he
fi ness
unc ion
,
he
unc ion
2can
be
defined
as
2(B)
=
1
−
co (B)
(4)
The
measu e
3is
based
on
a
di ec
anno a ion
file
om
a
biological
knowledge
eposi o y,
and
hence,
i
de e mines
how
he
biological
in o ma ion
is
in eg a ed
in
he
p ocess.
No e
ha
he
e m
3(B)
e alua es
he
se
o
genes
o
he
biclus e
B
bu
no
he
condi ions,
ha
is,
3has
he
same
alue
o
wo
biclus e s
wi h
he
same
se
o
genes
and
di e en
se s
o
condi ions.
The e o e,
3e alua es
he
biological
ele ance
o
a
biclus e
bu
i
canno
find
in e es ing
pa e ns
in
a
biclus-
e
and
i
canno
di e en ia e
biclus e s
wi h
he
same
se
o
genes.
Two
di e en
unc ions,
which
use
only
as
biological
da a
sou ce
a
di ec
anno a ion
file
wi h
he
in o ma ion
o
he
genes
in
he
gene
exp ession
ma ix,
a e
p oposed
o
he
measu e
3in
he
ollowing
Sec ions
2.2.1
and
2.2.2.
2.2.1.
F ac ional
Gene
On ology
measu e
A
measu e
based
on
he
analysis
o
he
en ichmen
o
a
biclus-
e
[39]
is
p oposed
in
his
pape
o
measu e
he
biological
ele ance
o
a
biclus e .
The
measu e
is
he
p opo ion
o
ac-
ion
o
genes
in
a
biclus e
associa ed
o
en iched
GO
e ms,
he eina e
F acGO.
The
e ms
wi h
an
adjus ed
p- alue
unde
a
gi en
h eshold
a e
said
o
be
en iched
o
o e ep esen ed.
This
h eshold
is
known
as
significance
le el
and
is
usually
se
o
0.05.
The
adjus ed
p- alue
o
each
anno a ed
e m
in
he
anno a ion
file
is
compu ed
wi h
espec
o
he
g oup
o
genes
ha
belong
o
he
biclus e .
The
uni e se
o
genes
is
he
comple e
se
o
genes
in
he
gene
exp ession
ma ix.
Fishe ’s
exac
es
has
been
used
o
de e mine
s a is ically
o e ep e-
sen ed
e ms
and
Bon e oni
es
has
been
used
o
co ec
he
adjus ed
p- alues
o
mul iple
compa isons
as
he
numbe
o
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
167
hypo heses
es ed
is
he
numbe
o
e ms
in
he
anno a ion
file.
Thus,
F acGO
is
defined
as
ollows:
F acGO(B)
=⎧
⎪
⎨
⎪
⎩
0
i J
=
0
1
J
·
N
J

i=1
xii J
≥
1(5)
whe e
J
is
he
numbe
o
en iched
GO
e ms,
namely
he
num-
be
o
GO
e ms
wi h
an
adjus ed
p- alue
less
han
0.05,
N
is
he
numbe
o
genes
in
he
biclus e
and
xiis
he
numbe
o
genes
o
he
biclus e
ha
p esen s
he
GO
e m
i
in
he
anno-
a ion
file.
No e
ha
F acGO
is
equal
o
1
i
all
he
genes
o
he
biclus e
a e
associa ed
wi h
all
en iched
GO
e ms
(xi=
N,
∀i
=
{1,
.
.
.,
J})
and
0
when
he e
is
no
an
en iched
GO
e m.
I
can
be
concluded
ha
F acGO
has
a
alue
o
1
o
biologically
ele an
biclus e s
and
0
o he wise.
In
his
case,
he
p oposed
unc ion
3can
be
di ec ly
defined
as
3(B)
=
1
−
F acGO(B)
(6)
I
can
be
no ed
ha
he
biclus e
B
is
conside ed
a
high-
quali y
biclus e
i
3is
equal
o
0
and
a
bad
biclus e
i
i s
alue
is
se
o
1.
2.2.2.
No malize
e m
o e lap
measu e
Se e al
gene
pai wise
GO-based
measu es
ha e
been
p oposed
in
he
li e a u e.
These
measu es
compu e
he
simila i y
be ween
wo
genes
based
on
hei
GO
anno a ions.
The
sim-
NTO
measu e,
which
is
based
on
he
e m
o e lap
defined
in
[32],
only
uses
anno a ion
files
as
inpu .
This
measu e
is
as e
and
simple
han
o he
measu es
based
on
in o ma ion
con-
en
(IC).
These
IC-based
measu es
use
he
GO
ee
s uc u e
as
addi ional
in o ma ion
along
wi h
he
anno a ion
file.
Sim-
NTO
cap u es
he
GO
hie a chical
s uc u e
i
he
anno a ion
files
a e
buil
by
con aining
all
pa en
e ms
o
each
e m.
A
measu e
based
on
he
unc ional
simila i y
o
a
biclus e
using
simNTO
measu e
is
p oposed
as
a
measu e
o
e alua e
he
biological
ele ance
o
a
biclus e
in
his
wo k.
This
mea-
su e
is
defined
by
means
o
he
a e age
o e lapping
be ween
he
pai s
o
genes
o
a
biclus e
acco ding
o
he
in o ma ion
om
he
GO
anno a ion
file.
Tha
is,
SimNTO(B)
=1
N
2
N−1

i=1
N

j=i+1
simNTO(gi,
gj)
(7)
whe e
N
is
he
numbe
o
genes
in
he
biclus e
B
and
sim-
NTO
is
he
no malized
e m
o e lap
measu e
p oposed
in
[32].
In
pa icula ,
simNTO
measu es
he
o e lapping
be ween
wo
genes
g1and
g2wi h
espec
o
GO
e ms
and
is
defined
as
simNTO(g1,
g2)
=|anno g1∩
anno g2|
min(|anno g1|,
|anno g2|)(8)
whe e
anno giis
he
se
o
GO
e ms
associa ed
o
he
gene
gi
and
|
·
|
is
he
numbe
o
elemen s
o
a
se .
I
is
impo an
o
men ion
ha
he
di ec
anno a ion
file
mus
be
buil
by
p op-
aga ing
he
e ms
owa d
he
uppe
le els
in
he
on ology
o
compu e
his
measu e.
The e o e,
anno giis
defined
by
consid-
e ing
he
se
o
all
di ec
anno a ions
o
he
gene
giand
he
associa ed
pa en
e ms
in
he
on ology,
excluding
he
oo
o
he
hie a chy.
Acco dingly,
he
anno a ion
file
mus
cap u e
he
GO
ee
s uc u e.
No e
ha
he
simNTO
measu e
anges
om
0
o
1.
Two
genes
sha e
he
same
anno a ions
and
a e
e y
simila
in
he
on ology
i
simNTO
has
a
alue
o
1,
and
0
o he wise.
Mo eo e ,
i
one
gene
g
is
no
con empla ed
in
he
anno a ion
file
because
he e
is
no
any
in o ma ion
in
GO,
anno gis
he
emp y
se ,
and
in
his
case,
he
simNTO
measu e
is
di ec ly
se
o
0.
In
his
case,
he
p oposed
unc ion
3is
defined
as
ollows:
3(B)
=
1
−
SimNTO(B)
(9)
I
can
be
app ecia ed
ha
3(B)
=
0
when
B
is
composed
o
a
g oup
o
genes
ha
sha e
simila
biological
unc ionali ies
in
GO,
and
he e o e,
B
is
a
ele an
biclus e
acco ding
o
GO.
2.3.
Desc ip ion
o
he
algo i hm
An
algo i hm
based
on
a
me aheu is ic
scheme
has
been
con-
side ed
due
o
he
compu a ional
na u e
o
biclus e ing.
The
sea ch
scheme
de i es
om
he
algo i hm
p esen ed
in
[25]
whe e
a
sca e
sea ch
was
also
applied
in
biclus e ing
o
gene
exp ession
da a.
The
p oposed
algo i hm
is
a
sequen ial
co e -
ing
algo i hm,
namely,
each
biclus e
is
ob ained
by
applying
an
independen
sca e
sea ch
p ocedu e.
This
i e a i e
p o-
cess,
join ly
wi h
he
bias
in oduced
in
he
sea ch
h ough
he
fi ness
unc ion
defini ion,
con ols
he
non-de e minis ic
na u e
o
he
p ocess.
The
sca e
sea ch
is
a
popula ion-based
e olu iona y
me aheu is ic
whe e
a
popula ion
o
solu ions
e ol es
un il
an
op imal
solu ion
is
eached.
The
basic
idea
in
he
sca e
sea ch
is
o
pe o m
he
op imiza ion
wi h
a
small
se
o
solu ions,
called
he
e e ence
se ,
ins ead
o
a
comple e
popula ion
o
solu ions
as
in
o he
popula ion-based
me aheu is ics
[40].
The
e e ence
se
is
composed
o
he
bes
solu ions
acco ding
o
in ensifica ion
and
di e si y
s a egies.
Fig.
1
shows
he
basic
idea
behind
he
p oposed
algo i hm.
All
he
s eps
composing
his
algo i hm
a e
going
o
be
b iefly
desc ibed
in
Sec ions
2.3.1
and
2.3.2.
2.3.1.
Sca e
sea ch
A
solu ion
ep esen s
a
biclus e ,
which
is
codified
by
wo
bina y
s ings
whe e
he
bi s
indica e
i
he
gene
o
condi ion
is
p esen
o
no
in
he
biclus e .
Fi s ly,
an
ini ial
popula-
ion
is
gene a ed
by
he
di e sifica ion
gene a ion
me hod
and
is
composed
o
solu ions
as
sca e
as
possible,
which
a e
hen
imp o ed
by
a
local
sea ch
p ocedu e
ha
will
be
desc ibed
in
Sec ion
2.3.2.
Con a y
o
he
gene ic
algo i hms
he
ini-
ial
popula ion
is
buil
ollowing
a
mechanism
o
achie e
di e sifica ion
and
no
a
gene al
andomiza ion
p ocess.
The
di e sifica ion
gene a ion
me hod
gene a es
a
collec ion
o
solu-
ions
om
a
seed
solu ion.
I
x
is
a
bina y
s ing
used
as
seed,
a
new
s ing
xis
gene a ed
o
each
alue
o
an
in ege
h
=
1,
2,
3,
.
.
.,
hmax as
ollows:
x
1+kh =
1
−
x1+kh o
k
=
0,
1,
2,
3,
.
.
.,
n/h(10)

168
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
Fig.
1
–
The
p oposed
sca e
sea ch
o
biclus e ing.
whe e
x
=
(x1,
.
.
.,
xn),
n
is
he
numbe
o
bi s,
k
akes
al-
ues
om
0
o
he
la ges
in ege
sa is ying
k
≤
n/h.
Due
o
he
bina y
s ing
size
and
o
he
sca e
sea ch
li e a u e
ecom-
menda ions
[40],
he
maximum
alue
o
h
is
hmax =
n/5.
All
he
emaining
bi s
o
xa e
equal
o
hose
o
x.
A e
gene a ing
all
he
possible
solu ions
wi h
ha
seed,
i
mo e
solu ions
we e
needed
in
he
ini ial
popula ion,
he
ule
will
be
applied
again
using
he
las
solu ion
as
a
new
seed.
This
me hod
is
he
s an-
da d
p ocedu e
usually
used
in
sca e
sea ch
algo i hms
wi h
bina y
codifica ion
[40].
The
idea
o
sca e
be ween
wo
solu-
ions
is
in oduced
by
he
Hamming
dis ance.
The
Hamming
dis ance
be ween
wo
bina y
s ings
is
defined
as
he
num-
be
o
posi ions
a
which
he
co esponding
0’s
and
1’s
a e
di e en .
Once
he
ini ial
popula ion
is
gene a ed,
he
e e ence
se
is
buil
by
he
build
e e ence
se
me hod.
This
me hod
consis s
in
selec ing
he
fi e
bes
solu ions
and
he
fi e
mos
sca e ed
solu ions
wi h
espec
o
he
emaining
o
exis ing
solu ions
in
he
se
om
he
ini ial
popula ion.
The e o e,
he
e e ence
se
con ains
he
mos
ep esen a i e
solu ions
om
he
ini-
ial
popula ion
acco ding
o
quali y
and
di e si y
c i e ia.
The
sca e
solu ions
p o ide
di e si y
in
he
sea ch
p ocess
o
a oid
local
op ima.
This
di e si y
s a egy
plays
a
simila
ole
o
he
mu a ion
ope a o s
in
gene ic
algo i hms,
o
example.
On
he
o he
hand,
he
quali y
solu ions
a e
conside ed
as
mechanism
o
define
an
in ensifica ion
s a egy
in
he
sea ch.
I
is
impo an
o
upda e
he
ini ial
popula ion
by
emo ing
he
solu ions
selec ed
by
his
me hod.
The
e e ence
se
e ol es
by
using
he
subse
gene a ion
me hod,
he
solu ion
combina ion
me hod
and
he
e e ence
se
upda e
me hod
un il
he
e e ence
se
is
s able.
Once
he
e -
e ence
se
does
no
change,
he
e e ence
se
is
ebuil
wi h
he
fi e
bes
solu ions
om
he
p e ious
e e ence
se
and
he
fi e
mos
sca e ed
solu ions
wi h
espec
o
he
emaining
solu ions
in
he
se
om
he
ini ial
popula ion.
The
subse
gen-
e a ion
me hod
gene a es
subse s
o
pai s
o
solu ions
om
he
e e ence
se
o
be
combined
by
he
solu ion
combina ion
me hod
wi h
he
pu pose
o
c ea ing
new
solu ions.
Once
he
new
solu-
ions
a e
ob ained,
he
local
sea ch
p ocedu e
is
again
applied
o
imp o e
hem.
The
solu ion
combina ion
me hod
is
based
on
he
uni o m
c osso e
ope a o
commonly
used
in
e olu ion-
a y
compu a ion.
The
e e ence
se
upda e
me hod
consis s
in
choosing
he
10
bes
solu ions,
acco ding
o
he
fi ness
unc-
ion,
om
he
joining
o
he
solu ions
o
he
e e ence
se
and
he
new
solu ions
ob ained
by
he
solu ion
combina ion
me hod.
The
ou pu
is
he
bes
biclus e
in
he
las
e e ence
se .
The
whole
p ocess
is
epea ed
as
many
imes
as
numbe
o
biclus e s
o
be
ob ained,
which
is
an
inpu
pa ame e
o
he
algo i hm.
No
mechanism
o
edundancy
con ol
among
esul s
has
been
conside ed
and
i
could
be
hough
ha
he
same
biclus e
is
always
ound.
Se e al
wo ks
based
on
me a-
heu is ics
include
mechanisms
o
edundancy
con ol
bu
hese
algo i hms
usually
use
only
an
ini ial
popula ion
in
he
comple e
p ocess.
Conc e ely,
he
algo i hm
published
in
[41]
p esen s
an
addi ional
e m
in
he
fi ness
unc ion
o
con ol
he
edundancy
in
o de
o
a oid
simila i ies
among
biclus e s
and
o
find
epea edly
he
same
biclus e .
Howe e ,
i
a
di e -
en
ini ial
popula ion
is
buil
o
each
biclus e
ob ained
by
he
p oposed
algo i hm,
his
addi ional
e m
can
be
emo ed
and
i
is
enough
fil e ing
hose
highly
edundan
biclus e s.
Mo eo e ,
i
is
in e es ing
o
ob ain
biclus e s
sha ing
g oups
o
genes
om
a
biological
poin
o
iew
[2,3].
Consequen ly,
he
p oposed
algo i hm
does
no
con empla e
an
addi ional
e m
in
he
fi ness
unc ion
and
builds
an
ini ial
popula ion
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
169
o
each
ound
biclus e .
An
o e lapping
h eshold
o
30%
is
chosen
and
he
biclus e s
wi h
an
o e lapping
g ea e
han
his
h eshold
a e
emo ed.
The
pa ame e s
o
he
algo i hm
ha e
been
chosen
acco d-
ing
o
ecommenda ions
o
he
li e a u e
o
sca e
sea ch
[40]
and
p e ious
wo ks
[25].
In
pa icula ,
200
o
he
size
o
he
ini ial
popula ion,
10
o
he
size
o
he
e e ence
se
and
20
o
he
numbe
o
i e a ions
o
he
e olu iona y
p ocess
( he
inne
loop
in
Fig.
1).
2.3.2.
Imp o emen
me hod
The
imp o emen
me hod
is
a
local
sea ch
p ocedu e
designed
o
imp o e
he
quali y
o
solu ions
acco ding
o
he
fi ness
unc ion.
Namely,
gi en
a
biclus e
his
me hod
gene -
a es
a
new
biclus e
wi h
a
be e
alue
o
i s
fi ness
unc ion.
In
gene al,
he
imp o emen
me hod
in
a
sca e
sea ch
is
specifically
designed
o
each
p oblem
as
i
depends
on
he
na u e
o
he
fi ness
unc ion
[25].
Al hough
an
imp o emen
me hod
guided
by
a
heu is ic
is
be e
han
a
blind
imp o e-
men
me hod,
he
heu is ic
o
imp o e
he
quali y
o
biclus e s
is
ela ed
o
he
fi ness
unc ion
o
he
p oblem.
In
his
wo k,
se e al
di e en
fi ness
unc ions
a e
analyzed,
namely
one
o
each
measu e
p oposed
o
in eg a e
biological
knowledge,
and
he e o e,
he
same
heu is ic
is
no
good
o
all
he
fi -
ness
unc ions.
Fo
his
eason,
a
blind
imp o emen
me hod
is
p oposed
wi h
he
pu pose
o
being
used
wi h
all
hem.
This
independence
o
he
imp o emen
me hod
ega ding
he
fi -
ness
unc ion
mo i a es
a
blind
sea ch
among
solu ions
close
o
he
o iginal
solu ion.
Some imes
his
sea ch
does
no
find
a
be e
solu ion,
and
he e o e,
in
hese
cases
he
o iginal
solu-
ion
is
no
imp o ed.
This
me hod
plays
an
impo an
ole
o
speed
up
he
con e gence
o
he
sea ch.
The
imp o emen
me hod
aims
a
selec ing
he
bes
biclus-
e
om
a
ce ain
numbe
o
new
biclus e s
gene a ed
by
he
combina ion
o
di e en
bina y
s ings.
These
new
solu ions
a e
gene a ed
by
means
o
pe mu a ions
(see
Fig.
2)
in
o de
o
be
close
(in
he
sense
o
he
hamming
dis ance)
o
he
o iginal
biclus e /solu ion.
No e
ha
he
new
solu ions
mus
imp o e
he
o iginal
solu ion
bu
in
he
same
“neighbo hood”.
I
new
biclus e s
do
no
imp o e
he
sea ch,
he
ou pu
is
he
o iginal
biclus e .
Fig.
2
shows
how
bina y
s ings
a e
combined.
These
bina y
s ings
ha e
been
ob ained
om
he
bina y
s ings
o
he
o iginal
biclus e
o
be
imp o ed.
In
pa icula ,
each
bi
o
he
bina y
s ing
o
he
o iginal
biclus e
is
analyzed
and
i
he
bi
is
se
o
0
hen
he
bi
o
he
new
bina y
s ing
is
also
se
o
0
and
i
he
bi
is
1,
hen
he
ollowing
ou
cases
a e
conside ed:
•
Case
1:
The
nex
bi
is
changed
o
1
and
he
cu en
bi
does
no
change
i s
alue.
•
Case
2:
The
nex
bi
is
changed
o
1
and
he
cu en
bi
is
changed
o
0.
•
Case
3:
The
p e ious
bi
is
changed
o
1
and
he
cu en
bi
does
no
change
i s
alue.
•
Case
4:
The
p e ious
bi
is
changed
o
1
and
he
cu en
bi
is
changed
o
0.
Twel e
new
biclus e s
ha e
been
gene a ed
by
applying
his
me hod.
I
he
new
biclus e s
do
no
imp o e
he
alue
o
he
fi ness
unc ion
o
he
o iginal
biclus e ,
he
ou pu
o
he
imp o emen
me hod
is
he
o iginal
biclus e .
3.
Expe imen s
The
goal
o
he
expe imen s
is
o
analyze
how
he
in eg a ion
o
biological
in o ma ion
has
a
ele an
influence
on
he
pe -
o mance
o
he
p oposed
algo i hm.
In
pa icula ,
he
esul s
ob ained
om
F acGO
and
SimNTO
measu es
p oposed
he e
in
o de
o
in eg a e
he
biological
knowledge
a e
compa ed.
Finally,
he
esul s
ob ained
by
he
p oposed
algo i hm
a e
compa ed
wi h
hose
o
he
classical
biclus e ing
algo i hms
such
as
ChCh
[5],
ISA
[10],
OPSM
[11]
and
xMo i s
[12]
ypically
used
as
benchma k
in
he
li e a u e.
The
s anda d
compa ison
me hodology
among
biclus e ing
algo i hms
is
usually
based
on
he
gene
en ichmen
in
he
ob ained
biclus e s
[6].
In
his
wo k,
a
biclus e
is
said
o
be
en iched
i
a
leas
one
en iched
GO
e m
is
associa ed
o
i .
This
sec ion
p esen s
he
expe imen s
ca ied
ou
o
assess
he
pe o mance
o
he
p oposed
algo i hm
on
he
da ase s
desc ibed
in
Sec ion
3.1.
The
esul s
a e
ga he ed
in
Sec ion
3.2
and
a
discussion
can
be
ound
in
Sec ion
3.3.
3.1.
Da a
se s
Two
yeas
da ase s
wi h
accession
numbe s
GDS1116
and
GDS2914
om
he
GEO
eposi o y
[42]
ha e
been
used
in
he
expe imen a ion.
The
fi s
one
is
composed
o
7085
exp ession
p ofiles
and
131
samples
and
ecollec s
he
gene ic
a ia ion
in
he
gene
exp ession
be ween
pa en s
and
p ogenies
om
a
c oss
o
wo
di e en
kinds
o
yeas
s ains.
The
second
one
has
15,488
exp ession
p ofiles
and
36
samples
and
is
a
ime
cou se
expe imen
in
which
yeas
cells
deal
wi h
a
low
dose
o
ca eine
a e
analyzed.
The
aw
da a
ha e
been
p o-
cessed
wi h
he
Babelomics
web
ool
[43].
Fo
bo h
da ase s,
he
exp ession
p ofiles
wi h
mo e
han
a
30%
o
missing
al-
ues
ha e
been
fil e ed
and
he
emaining
missing
alues
ha e
been
eplaced
wi h
he
mean
o
he
alues
in
he
p ofile.
The
p ofiles,
which
appea
se e al
imes
bu
ep esen ing
he
same
gene,
ha e
been
summed
up
by
means
o
he
median
o
he
alues.
A e
p ocessing
he
aw
da a,
GDS1116
exp ession
ma ix
is
a
ma ix
composed
o
882
genes
and
131
samples
o
expe imen al
condi ions
and
GDS2914
a
ma ix
o
975
genes
and
36
condi ions.
Biological
in o ma ion
is
p o ided
by
a
di ec
anno a ion
file
om
biological
p ocess
domain
(BP)
o
Gene
On ology
(GO).
This
file
shows
he
GO
e ms
associa ed
wi h
each
gene
o
he
da a
se .
No e
ha
his
in o ma ion
could
be
downloaded
om
GO
in
di e en
ways.
In
his
wo k,
he
ee
s uc u e
o
GO
is
conside ed
and
he
anno a ion
file
has
been
ob ained
by
p op-
aga ing
he
anno a ions
o
he
uppe
le els
in
he
on ology.
Tha
is,
each
gene
is
also
ela ed
o
GO
e ms
co esponding
o
all
pa en
nodes
un il
he
oo
node.
The
anno a ion
files
o
bo h
da ase s
ha e
been
gene a ed
by
he
Babelomics
ool
wi h
de aul
op ions.
Fo
GDS1116
da a
se ,
632
genes
a e
anno a ed
in
he
file
om
he
882
genes
o
he
exp ession
ma ix.
This
file
con ains
245
di e en
GO
e ms
and
he
a e age
numbe
o
GO
e ms
pe
gene
is
equal
o
10.6.
Fo
GDS2914
da a
se ,
658
genes
a e
anno a ed
om
a
o al
numbe
o
975
genes,
he
file
170
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
Fig.
2
–
The
p oposed
imp o emen
me hod:
a
es
example.
con ains
256
GO
e ms
and
he
a e age
numbe
o
GO
e ms
pe
gene
is
10.1.
3.2.
Resul s
In
his
sec ion
he
esul s
a e
ga he ed
wi h
he
pu pose
o
e alua ing
he
impo ance
o
in eg a ing
biological
knowledge
o
find
high-quali y
biclus e s.
The
esul s
ob ained
om
he
p oposed
algo i hm
o
di e en
configu a ions
o
he
fi -
ness
unc ion
a e
p esen ed
and
compa ed
wi h
espec
o
se e al
ypical
a iables
such
as
he
size
o
biclus e s,
o e -
lapping
among
biclus e s
and
en ichmen
o
biclus e s.
Also,
he
esul s
ob ained
om
di e en
eposi o ies
such
as
GO,
KEGG
pa hways
and
In e P o
a e
p esen ed.
Each
un
o
he
algo i hm
ob ains
100
biclus e s.
This
numbe
has
been
cho-
sen
because
o
ob ain
a
high
numbe
o
biclus e s
is
desi able
due
o
he
compa ison
among
biclus e ing
algo i hms
is
usu-
ally
es ablished
in
e ms
o
pe cen ages
o
en iched
biclus e s.
No e
ha
he
algo i hm
ob ains
each
biclus e
h ough
an
independen
non-de e minis ic
p ocedu e.
Table
1
p esen s
he
pe cen age
o
en iched
biclus e s
ob ained
by
he
p o-
posed
algo i hm
o
di e en
numbe s
o
biclus e s
(namely,
10,
50
and
100).
I
can
be
obse ed
ha
he
pe cen age
does
no
depend
on
he
numbe
o
biclus e s
conside ed
as
inpu
pa ame e .
The
fi ness
unc ion
pa ame e
se ing
is
expe i-
men al
s udied
o
analyze
he
pe o mance
o
he
biological
in eg a ion
measu es.
Table
2
summa izes
he
quali y
o
biclus e s
ob ained
by
he
p oposed
algo i hm
o
GDS1116
and
GDS2914
da ase s
when
di e en
configu a ions
o
he
fi ness
unc ion
ha e
been
conside ed.
Specifically,
he
column
Measu e,
indica es
i
he
fi ness
unc ion
akes
in o
accoun
biological
in o ma-
ion
by
means
o
he
measu es
SimNTO
(Eq.
(7))
o
F acGO
(Eq.
(6))
o
no
( 3=
0
in
Eq.
(1)).
The
column
Pa ame e s
ep esen s
he
weigh
co esponding
o
each
e m
o
he
fi ness
unc ion.
I
is
impo an
o
highligh
ha
all
e ms
i a y
be ween
0
and
1.
Gi en
he
impo ance
o
a oiding
i ial
biclus e s
wi h
a
low
numbe
o
genes
o
condi ions,
o
example
only
wo
genes
o
condi ions,
he
pa ame e
M1associa ed
o
he
ol-
ume
o
he
biclus e
always
has
been
se
o
2
[25].
Namely,
he
ollowing
h ee
configu a ions
ha e
been
analyzed
when
he
biological
knowledge
is
in eg a ed
in
he
fi ness
unc ion:
o
find
biclus e s
wi h
unde lying
co ela ed
pa e ns
and
o
find
biological
high-quali y
biclus e s
a e
equally
impo an
(M2=
1,
M3=
1),
o
find
biclus e s
wi h
co ela ed
pa e ns
is
mo e
impo an
han
o
find
biological
high-quali y
biclus-
e s
(M2=
2,
M3=
1)
o
ice- e sa
(M2=
1,
M3=
2);
when
he
algo i hm
sea ches
o
biclus e s
wi hou
a
p io i
biological
knowledge
(M3=
0),
wo
configu a ions
ha e
been
analyzed
depending
on
he
ele ance
o
finding
biclus e s
wi h
enclosed
pa e ns
(M2=
1
o
M2=
2).
No e
ha
M1canno
be
equal
o
ze o
o
a oid
i ial
biclus e s
[25].
On
he
o he
hand,
i
M2=
0
he
numbe
o
condi ions
is
no
co ec ly
con olled
by
he
fi ness
unc ion,
and
he e o e,
he
algo i hm
is
no
a
biclus-
e ing
algo i hm
because
can
clus e
genes
bu
no
condi ions.
Finally,
M3=
0
is
conside ed
when
biological
in o ma ion
is
no
conside ed.
The
nex
columns
in
Table
2,
size,
en iched
biclus e s
(%),
GO
e ms
pe
biclus e
and
ime,
show
he
a e age
numbe
o
genes
and
condi ions
o
100
biclus e s
ob ained
by
he
p oposed
algo i hm,
he
pe cen age
o
en iched
biclus e s,
he
a e age
numbe
o
en iched
GO
e ms
pe
biclus e
and
he
compu a ion
ime
o
he
algo i hm
o
ob ain
a
biclus e ,
espec i ely.
Al hough
he
en ichmen
o
biological
signifi-
cance
o
GO
e ms
is
usually
s udied
ega ding
he
biological
p ocess
(BP)
domain
o
GO,
in
his
wo k
he
biological
signifi-
cance
has
been
also
s udied
o
molecula
unc ion
(MF)
and
cellula
componen
(CC)
domains.
No e
ha
he
pe cen age
o
en iched
biclus e s
is
he
s anda d
biological
e alua ion
c i-
e ion
commonly
used
in
biclus e ing
[6,44].
I
should
also
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
171
Table
1
–
Pe cen age
o
en iched
biclus e s
ob ained
by
he
p oposed
algo i hm
o
di e en
numbe s
o
biclus e s.
Fi ness
unc ion
configu a ion
Numbe
o
biclus e s
(M1,
M2,
M3)
En iched
biclus e s
(%)
BP
MF
CC
1-SimNTO
10
(2,1,1)
100
100
100
1-SimNTO
50
(2,1,1)
100
98
100
1-SimNTO
100
(2,1,1)
99
97
97
1-F acGO
10
(2,1,1)
100
70
50
1-F acGO
50
(2,1,1)
100
72
64
1-F acGO
100
(2,1,1)
100
73
67
0
10
(2,1,0)
85
82
88
0
50
(2,1,0)
82
72
84
0
100
(2,1,0)
85
82
88
Table
2
–
Resul s
ob ained
by
di e en
fi ness
unc ion
configu a ions
o
bo h
da ase s.
Each
ow
shows
a
un
ha
ob ains
100
biclus e s.
Da ase
Fi ness
unc ion
Size
En iched
biclus e s
(%)
GO
e ms
pe
biclus.
(BP)
Time
(s)
Measu e
3Pa ame e s
(M1,
M2,
M3)
BP
MF
CC
(2,
1,
1)
(11.6
×
15.6)
99
97
97
5.74
28.65
1-SimNTO
(2,
1,
2)
(8.7
×
15.2)
87
75
84
3.67
15.78
(2,
2,
1)
(10.1
×
5.1)
95
83
89
4.5
24.03
GDS1116
(2,
1,
1)
(181.6
×
19.4)
100
73
67
1
5410.98
1-F acGO
(2,
1,
2)
(193.9
×
19.3)
100
79
79
1
5546.12
(2,
2,
1)
(109.2
×
3)
100
47
52
1
5682.65
(2,
1,
0)
(23.5
×
14.7)
85
82
88
2.16
38.29
0
(2,
2,
0)
(46.8
×
3.2)
25
17
21
0.4
11.51
(2,
1,
1)
(10.9
×
10.9)
87
33
33
5.45
27.76
1-SimNTO
(2,
1,
2)
(8.0
×
10.2)
65
24
33
2.94
15.67
(2,
2,
1)
(9.5
×
3.3)
87
25
30
5.39
22.18
GDS2914
(2,
1,
1)
(180.6
×
15.1)
100
97
94
1.01
5420.84
1-F acGO
(2,
1,
2)
(193.2
×
15.8)
100
98
94
1
5920.09
(2,
2,
1)
(102.8
×
3)
100
72
67
1
6311.43
(2,
1,
0)
(24.1
×
9.0)
2
5
6
0.02
13.14
0
(2,
2,
0)
(37.1
×
3.1)
13
15
17
0.19
7.16
Fig.
3
–
Pe cen age
o
en iched
biclus e s
o
GDS1116
om
Tables
2
and
3.
178
c
o
m
p
u
e
m
e
h
o
d
s
a
n
d
p
o
g
a
m
s
i
n
b
i
o
m
e
d
i
c
i
n
e
1
1
9
(
2
0
1
5
)
163–180
Fig.
11
–
GO
e m
clus e s
epo ed
by
Re igo
om
biclus e
1
o
he
F acGO
measu e
and
211
configu a ion.
Only
wo
gene al
GO
e ms
a e
epo ed:
p o ein-ubiqui ina ion
and
me abolism.
measu e
cap u es
biclus e s
whe e
genes
a e
oge he
in
a
same
GO
e m,
and
as
a
consequence,
hei
genes
a e
anno-
a ed
in
he
uppe
le els
o
he
GO
hie a chy.
No e
ha
he
anno a ion
files
used
as
inpu
pa ame e
a e
gene a ed
cap-
u ing
all
he
associa ed
pa en
e ms
o
each
gene.
Gene
Te m
Linke
[48]
and
Re igo
[49]
ools
ha e
been
used
o
con-
fi m
ha
he
biclus e s
based
on
he
F acGO
measu e
show
e y
gene al
GO
in o ma ion.
Fi s ly,
he
fi s
ool
fil e s
i ele-
an
GO
in o ma ion
by
iden i ying
me ag oups
o
genes
wi h
cohe en
biological
significance.
Secondly,
Re igo
summa izes
a
lis
o
hese
GO
e ms
by
finding
ep esen a i e
subse s
o
e ms
using
a
clus e ing
p ocedu e
ha
emo es
edundan
e ms.
Fig.
11
shows
he
significan
en iched
GO
e m
in
he
fi s
biclus e
ob ained
by
he
F acGO
measu e
and
211
con-
figu a ion.
All
en iched
GO
e ms
ha e
been
clus e ed
in
wo
e y
gene al
e ms
in
GO:
me abolism
and
p o ein
ubiqui-
a ion.
A e
ha ing
applied
his
pipeline
analysis,
Gene
Te m
Linke
and
Re igo,
all
epo ed
en iched
GO
e ms
a e
clus-
e ed
in
gene al
GO
e ms.
The e o e,
he
assump ion
ha
F acGO-based
biclus e s
a e
composed
o
genes
anno a ed
in
he
uppe
le els
o
he
GO
hie a chy
is
confi med.
The
F acGO
measu e
finds
biclus e s
wi h
a
gene al
in o ma ion
in
GO,
and
hence,
hese
biclus e s
a e
composed
o
genes
ha
a e
no
ela ed
as
g oup
wi h
any
pa hway.
The
comple e
in o ma ion
o
all
figu es
can
be
ead
as
Supplemen a y
in o ma ion.
4.
Conclusions
A
sca e
sea ch-based
biclus e ing
algo i hm
ha
in eg a es
biological
in o ma ion
has
been
p oposed
in
his
pape .
The
da a
inpu
o
he
p oposed
algo i hm
a e
he
gene
exp es-
sion
ma ix
and
a
di ec
anno a ion
file
linking
genes
wi h
se s
o
biological
e ms
ex ac ed
om
a
biological
eposi o y
o
da abase.
The
Gene
On ology,
KEGG
pa hways
and
In e P o
da abases
ha e
been
used
as
sou ce
o
gene a ing
hese
files
in
his
wo k.
Two
di e en
biological
measu es,
F acGO
and
SimNTO,
ha e
been
p oposed
o
in eg a e
his
in o ma ion
by
means
o
i s
addi ion
o
he
fi ness
unc ion
o
be
op imized
o
e alua e
he
quali y
o
he
biclus e s
in
he
sca e
sea ch.
The
measu e
F acGO
is
based
on
he
biological
en ichmen
and
SimNTO
is
based
on
he
o e lapping
among
GO
anno a ions
o
pai s
o
genes.
Expe imen al
esul s
om
he
applica ion
o
he
p oposed
algo i hm
o
wo
da ase s
ha e
been
epo ed
and
discussed
showing
a
be e
pe o mance
when
biological
knowledge
is
in eg a ed
and
be e
biclus e s
han
ha
o
he
classical
biclus e ing
algo i hms.
The
main
mo i a ion
has
been
o
use
a
s anda d
biolog-
ical
alida ion
c i e ion
in
biclus e ing
[6,44]
as
mechanism
o
in eg a e
biological
knowledge.
This
c i e ion
is
based
on
he
pe cen age
o
en iched
biclus e s
ha
is
calcula ed
using
di ec
anno a ion
files.
I
hese
files
a e
GO
files
which
ha e
been
gene a ed
by
p opaga ing
anno a ions
o
uppe
le els
in
he
GO
hie a chy,
he
expe imen al
esul s
show
ha
F acGO-
based
biclus e s
only
sha e
gene al
GO
e ms
and
hey
do
no
cap u e
ele an
biological
in o ma ion.
In
his
case,
he
Sim-
NTO
measu e,
which
is
based
on
he
e m
o e lap
defined
in
[32]
and
uses
anno a ion
files
as
inpu ,
is
as e
and
simple
han
o he
GO
seman ic
measu es
and
sol es
his
p oblem.
Se e al
expe imen s
show
ha
SimNTO-based
biclus e s
cap u e
el-
e an
biological
in o ma ion
ha
p esen
pa hways
mapping
in
Reac ome,
o
example.
I
is
impo an
o
no e
ha
SimNTO
cap u es
he
GO
hie a chical
s uc u e
i
he
anno a ion
files
con ain
all
pa en
e ms
o
each
e m.
As
a
summa y,
he
di -
e ences
be ween
he
F acGO
and
SimNTO
measu es
depend
on
he
da a
sou ce
and
how
he
anno a ion
file
has
been
buil
in
he
case
GO
is
used.
Fu u e
wo k
will
be
ocused
on
he
s udy
o
o he
biolog-
ical
measu es
o
handle
mic oRNA/mRNA
da a
and
how
o
in eg a e
in o ma ion
om
di e en
biological
sou ces.
Some
imp o emen s
in
he
sea ch
p ocedu e
o
he
p oposed
algo-
i hm
will
be
also
analyzed
such
as
he
se ing
configu a ion
o
inne
pa ame e s.
Conflic s
o
in e es
We
decla e
ha
we
ha e
no
any
ac ual
o
po en ial
compe ing
financial
in e es s.
Acknowledgmen s
We
would
like
o
hank
Spanish
Minis y
o
Science
and
Inno-
a ion,
Jun a
de
Andalucía
and
Uni e si y
Pablo
de
Ola ide
o
he
financial
suppo
unde
p ojec s
TIN2011-28956-C02-02,
P12-TIC-1728
and
APPB813097,
espec i ely.
Appendix
A.
Supplemen a y
da a
Supplemen a y
da a
associa ed
wi h
his
a icle
can
be
ound,
in
he
online
e sion,
a
h p://dx.doi.o g/10.1016/j.
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