BIOLOGY
OF
Different
JOHN
(1991)
Combinations
of Regulatory
Elements
May Explain Why Placenta-Specific
Expression
of the Glycoprotein
Hormone
a-Subunit
Gene Occurs Only
in Primates
and Horses1
NILSON,2
H.
231-237
44,
REPRODUCTION
A. BOKAR,
JOSEPH
Department
M. CLAY,
COLIN
DEBORA
TODD
L. HAMERNIK,
of Pharmacology,
Case
A, FARMERIE,
and
Western
Cleveland,
RUTH
Reserve
Ohio
ROBERT
A. FENSTERMAKER,3
A. KERI
University,
School
of Medicine
44106
ABSTRACT
Expression
and
horses.
are
required
CRE
binds
In
glycoprotein
humans,
two
for
also
that
indicates
a-subunit
gene.
change
that renders
In contrast,
although
CRE
but
appears
with
the
horse
the
of expression
to retaln
has
of the
sequence
of the
of
URE.
been
retained
has
Chorionic
gonadotropin
protein
hormones
unit, Expression
tary
of all mammals
and
been
gene
This
suggests
FSH, and
a-subunit
and
to the
TSH)
gene
that
either
a different
a completely
glyCo-
ular
expression
trast, while
progress
events
in placenta
has been
underlying
of primates
and
their
tissue-specific
search
(D.L.H.),
accessory
Grant
C. Clay
Ohio
P30
is the
CA 43730,
recipient
School
John
of Medicine,
OH
44106.
3Current
2074
and
the
of a grant
Institutes
RA.F.),
Ohio
from
the
Abington
Case
FAX:
H. Nilson,
Western
Ph.D.,
Reserve
Division
Road,
Cleveland,
of Neurosurgerv,
OH
and
express
to cAMP.
a functional
lacks
cognate
to
nuckotide
responsiveness
region
the
a number
Indirect
fail
to a single
protein
interacts
elements
less
is known
of Health
GM-07382
Edison
Grants
(JAB.,
involved
primates
and
AM- 28559
is required
Biotechnology
American
Heart
Center
Association,
Professor,
University,
Department
2119
(J.H.N.).
Northeast
Road,
University
Hospitals
equine
to be cloned.
understanding
the
synthesis
This
has
of CG,
involved
of
CG
molec-
we
have
why it is exin placenta
of
systematic
anal-
-146
and
Cleve-
and
origin.
These
elements
is referred
to as the
to bind
of Cleveland,
tinct
231
protein
[16].
located
upstream
placenta
regions,
of different
reflecting
are
human
in the
-180
and
The element
a protein
result
probably
elements
of the
are
binding
[10, 14, 18-
Expression
sequence
expression
cells and, presumably,
be subdivided
into two
44106.
is the
evolutionary
between
nucleotides
site of transcription,
appears
primates
elements,
DNA
DNA-protein
animals
major
findings
that have
of the a-subunit
gene
regulatory
for Placenta-Speqflc
a-Subunit
Gene
two
least
studies,
transgenic
summarize
the
that expression
of horses
gion
start
Re-
of Pharmacology,
Abington
encoding
gene
and addressed
of all mammals
but
transfection
by PCR, and
in placenta
[10-151.
(J.H.N.),
Cancer
genes
in the
horses.
combinations
Requirements
of the Human
about
RA.K.),
the
genes
have yet
approach
toward
an independent
216-368-3395.
address:
from
that
of regulatory
of
21, 351. Below,
we
led us to conclude
Affiliate.
2Correspondence:
land,
(TA.F.,
set
(CRE),
whereas
expression.
mammals
be traced
element
different
including
gene
assays,
cloning
made
in understandplacenta-specific
Even
by National
DK-0731
can
on the a-subunit
in the pituitary
At
This work was supported
gene
the protein
that confers
the promoter.regulatory
placenta-specific
HD07138-03
to placenta
primates
ysis of promoter-regulatory
regions
of the genes
encoding
the a-subunits
of humans,
cattle,
and horses.
Our approach
has entailed
the use of a variety
of experimental
techniques
and characterized
[5, 8], little
mechanisms
responsible
for
expression,
cattle
mechanisms
only
mammals
known
the a and CGI3
of the human
a-subunit
gene
[10-181.
In conthe genes
encoding
the 13-subunits
of human
LH and CG have been
cloned
is known
about
the molecular
element
a-subunit
from
expression
focused
pressed
[1,6].
Recently,
much
the molecular
and
(eCG)
as these
As an initial
protein
pituitary
genes
are located
on different
chromosomes
[9]; presumably this also applies
to equidae,
Although
there
are reports
of gonadotropin
activity
in placenta
of other
mammals,
CG
has been
defined
chemically
in only primates
and horses
ing
of only
response
for placenta-specific
in placenta
of rodents
in placenta
unique
of the
potential
even
or that
and a unique
13-suboccurs
in the pitui-
The latter are also the only
CG13 genes
[1, 5, 81, In humans,
possess
a protein
region
the
suggests
conserved,
in placenta
expression
is a heterodimeric
common
[1-61
binds
regulated
[6,7],
equidae
to
(LH,
of the
URE
but
cAMP
and
in horses.
(CG)
of an a-subunit
The
(URE)
promoter-regulatory
OVERVIEW
composed
of all mammals
element
these
genes
incapable
of binding
gene occurs
in horse
placenta,
placenta-specific
expression
gene.
of the
protein
pituitary
in the
regulatory
a-subunit
a-subunit
a-subunit
a functional
to provide
for placenta-specific
URE
occurs
upstream
analysis
URE-binding
the CRE-like
expression
URE
of the
Comparative
a functional
gene
termed
expression
that
Lack
a-subunit
elements,
protein.
indicates
evidence
hormone
different
placenta-specific
a ubiquitous
of mammals
the
of the
5’-flanking
for
gene
re-
-100
relative
to the
between
-180
and
regulatory
unique
required
a-subunit
element
(URE)
to choriocarcinoma
[10, 11, 15]. The URE may
each of which
binds
a dis-
232
NILSON
the
Alone,
URE
has
no
URE activity
is completely
quence
element
located
effect
on
[10, 11].
transcription
dependent
between
-146
ET AL.
on the adjacent
and -110.
This
quently,
acting
se36-
the
a tripartite
elements
human
domain
composed
defines
a-subunit
the
of two
placenta-specific
different
cLc-
enhancer
of
gene.
bp sequence
is composed
of two 18-bp
direct
repeats
Containing
a conserved
palindrome
TGACGTCA.
Each repeat
is
designated
as a cAMP
a single
18-bp
response
element
can
element,
confer
or
GRE,
either
the minimal
a-subunit
promoter
(-100
a heterologous
promoter
[10-12].
Furthermore,
binds
a ubiquitous
binding
protein
base within
the
43-kDa
because
cAMP-responsiveness
nuclear
to
The Proximal
Promoter
from
Cattle and Rodents
to
+
44) or
each
phosphoprotein
CRE
(CRE
unit
or CREB [22-24]).
Changing
virtually
any
core palindrome
disrupts
binding
of CREB
moter
mouse
The
CREs differ
from
URE
the
because
they
function
dependently
to confer
cAMP responsiveness
to
ogous
promoter
[10, 11]. Thus,
cAMP responsiveness
sue-independent
expression.
and one
promoter
and
superimposed
on
in-
or to a heterologous
CREs
they
promoter
are essential
unmask
the
dif-
-
of the a-subunit
genes
of bovine,
only a single
homolog
of the human
homologs
from
these
three
species,
rat, and
a CRE.
however,
of the
transition
have
To test
tors
this
shown
possibility,
we
constructed
in Figure
1 and
tested
the bovine
and, preof the human
a CRE
absence
the
their
of a func-
expression
activity
after
vectrans-
-cAMP
(-3l3)
pBo(CAT
-
-
,_..
(+48)
-E-
+
cAM P
I---
CAT
-
(-hO)
(-100/-114)
(+48)
(-170)
(-100/-114)
(+48)
pHuBOCCAT
p(AI8)HuBcCAT
(-166)
pBo(*CAT
---j
i-..
-:.LJ””
(+48)
0
0.5
1.0
CAT
1.5
a
human
a
disrupts
1---
CAT
-
human
a-subproximal-pro-
tional
GRE in the proximal-promoter
region
of the a-subunit gene
of bovine,
rat, and mouse
may explain
why the
a-subunit
gene
is silent
in the placentas
of these
mammals.
for placenta-specific
exprestissue-specific
properties
of
URE. In addition,
the URE and CREs together
have all
properties
of a classical
enhancer
[10, 11, 17]. Conse-
pSVOCAT
feature
of the
[18] that the
the perfect
palindrome
and renders
sumably,
the mouse
and rat homologs
incapable
of binding
CREB [18].
Because
the URE alone
is inactive,
tissue-specific
[11, 17]. Stated
a unique
we reported
of the a-Subunit
Gene
a Functional
CRE
C to T transition
at the fourth
position
TGACGTCA
sequence
[18, 25, 26]. This
a heterolis tis-
The latter property
emerges
only when
the URE
or two CREs are linked
to the minimal
a-subunit
ferently,
the
sion because
CREs are
Recently,
regions
contain
The
[14],
the
the
Tandem
gene.
Region
Lacks
5.0
10.0
Activity
FIG. 1. A single nucleotide
transition
creates
a functional
CRE and restores
activity
to the bovine
n-subunit
promoter
after transfection
in human
choriocarcinoma
cells. pSVOCAT
and pBaCAT
were constructed
by fusing the indicated
promoter-regulatory
regions from either the Rous sarcoma
virus
or the bovine n-subunit gene by ligation
into the Hindlhl site in pSVOCAT
110, 18). pHuBaCAT
contains
the human a sequence
(-170
to -100)
linked directly
to the downstream
sequence
(-114
to +48) of the bovine promoter,
forming
a hybrid promoter-regulatory
region containing
the human
URE-CRE
linked
to the bovine
promoter.
p(s18)HuBaCAT
is identical
to pHuBoCAT
except that one copy of the tandem
CREs has been deleted.
pBa*CAT
contains
the
bovine a 5’-flanking
sequence
(-166
to +48), with a point mutation
that creates a functional
CRE (T to C at position
-136),
linked to CAT. The resulting
constructs were transfected into BeWo choriocarcinoma
cells 110, 18). Each transfected
plate was subcultured;
half of the cells were treated with medium
containing
1 mM 8-Br-cAMP,
and the other half were given control medium.
Cell lysates were prepared
and subsequently
tested for CAT activity (271. The
values reported
for CAT activity
are means
and SEM from an average
of six transfections
(minimum
of three).
CAT activity
is expressed
as percent
conversion
per hour per 100 micrograms
of protein.
Reproduced
with permission
from Bokar et al. 1181,
a-SUBUNIT
fection
into
observations
human
choriocarcinoma
that warrant
consideration.
specific
enhancer
100;
minimal
URE plus
bovine
of the
human
GENE
cells.
IN PRIMATE
There
are three
First, the placenta-
a-subunit
two tandem
GREs)
a-subunit
promoter
EXPRESSION
gene
conferred
(region
HORSE
AND
to determine
of functional
(-170
to
activity
-114
to
to a
+ 48;
if there
is a correlation
between
the presence
GRE and placental
expression
of the a-subunit
gene.
Oligodeoxyribonucleotides
flanking
the human
a-subunit
served
between
the
construct
pHuBaCAT).
This suggested
that inactivity
of the
parent
bovine
construct,
which
contains
313 bp of 5’-flanking sequence
(pBaCAT)
was due to a defective
placentaspecific
enhancer.
Second,
a truncated
human
a-subunit
used as primers
primate
genes
enhancer
containing
ferred
activity
to the
zee)
the URE and only one GRE still
bovine
promoter
(p(M8)HuBaCAT),
but to a lesser
extent.
This suggested
tional
GRE was required
to unmask
tivity of the human
URE.
bovine
a-subunit
promoter
GRE. This change
shown).
Activity
(pBa*CAT)
was
restored
of this
identical
of the
cells
a single nucleotide
change
sequence
of the bo-
CREB binding
activity
(data
modified
bovine
promoter
to activity
of the
minimal
Thus,
unit
for placenta-specific
gene
confers
potential
Mouse Placenta
Factors Required
a-Subunit
Gene
Although
plain
why
dents
critical
and cattle,
trans-acting
that
the
is also
gene
placentas
factors,
required
for
from
such
from
for CAT activity,
tive, consistent
above
human
the
URE-binding
centas.
binding
expression
used
monkeys
[33], these
data
in conjunction
with a URE,
gene
of tandem
of
lower
GREs
was
primates
a recent
indicates
that
evolutionary
P1
P3
p
TATA
-149
103
ttacacca
in placentas
of ro-
Gorilla
ate
aaattgacgtcatggtaa
aaattgacgtcatggtaa
ttacacca
these
species
may
as the URE-binding
also lack
protein
Baboon
ate
aaattgacgteatggtaa
ttacacea
Rhesus
ate
aaattgacgteatggtaa
ttaeaeca
Horse
ate
aaattgaIgteat-taa
ttaea3a
Cattle
at
aaattgalgteatggtaa
ttaIQa
Sheep
aQ
aaattgalgteatggtaa
ttaIQa
Pig
ate
aaattgalgtcatggtaa
ttaeaea
Rabbit
ate
aaattgalgtcatggtaa
ttacaeca
Dog
ate
aaattgaIgtcatgtaa
ttacaa
Mouse
ate
Rat
ate
further
important
expression.
test
To
examined
in mammalian
suggests
for
genes
PCR [28, 29] to survey
regions
from
several
r
P2
aaattgacgtcatggtaa
is conserved
ac-
event.
aaattgacgtcatggtaa
was acreported
as well.
Gene
Event
aattgalgtcatggtaa
aaatgaIgtcatggtaa
ttalaeea
ttalaeea
pla-
that the UREplacenta-specific
The Tandem
CREs of the Human
a-Subunit
to be the Product
of a Recent Ez’olutionary
We have
moter-regulatory
and rhesus
GRE, acting
ate
is silent
of
direct
placenta-specific
expression
of the
Furthermore,
the presence
of a single
GRE
a-subunit
a
b
cells. Thus,
expression
of the
in mouse
placenta
suggests
that
of other
genes
P.Chimp
is sufficient
transgene
studies
be
Since
[31,32]
a single
a-subunit
and rhesus
monkey)
contain
GG is synthesized
in placentas
to ex-
GRE
only the human
a CAT
with the gene
transfection
of a number
In contrast,
ttacacca
were
Such
conservation
protein
may
GREs.
(baboon
bona
fide
genes
of
chimpan-
aaattgacgtcatggtaa
embryos
protein
18] were
aaattgacgtcatggtaa
mouse
for choriocarcinoma
a CAT transgene
[2-4,
atc
placenta-specffic
transgenic
the
genes
expression.
this possibility,
we established
lines of transgenic
mice containing
chimeric
constructs
composed
of the chloramphenicol acetvltransferase
(CAT)
gene
[27] linked
to the promoter-regulatory
region
of either
the human
(-1
500 to
+45)
or bovine
(-313
to +48)
a-subunit
gene
[18]. When
placentas
GRE.
is sufficient
to
a-subunit
gene.
in
bovine
Human
of a functional
a-subunit
tandem
monkeys
of baboons
suggest
that
quisition
and
GRE (Fig. 2b [30,35]).
The a-subunit
higher
primates
(gorilla
and pygmy
contain
World
a single
human
to regions
relatively
con-
(P3 and P2; Fig. 2a). Sequence
analysis
of
revealed
at least one copy of a perfectly
con-
retention
of a functional
region
of the bovine
a-sub-
Contains
All the Necessary
trans-acting
to Support
Expression
of the Human
absence
18-bp
and
corresponding
GRE that were
bovine
promoter
linked
to the truncated
human
placenta-specific
enhancer
(pM 8). This suggests
that the bovine
URE was as
active
as the human
URE even though
their
sequences
differed
by two nucleotides.
URE in the promoter-regulatory
served
humans
Old
funcac-
Finally,
complete
rescue
in human
choriocarcinoma
could
be achieved
by introducing
(1 to C) in the core palindromic-like
vine
not
that only a single
the placenta-specific
con-
233
PlACENTA
Appear
the proximal
prodifferent
mammals
FIG. 2. PCR analysis
of the proximal
promoter
regions of mammalian
a-subunit
genes. (a) The proximal
promoter-regulatory
region
of the human
glycoprotein
hormone
a-subunit
gene contains
two major
regulatory
elements-an
upstream
regulatory
element
(URE) and a tandemly
repeated
cAMP response
element
(CRE). Arrows
indicate
regions
over which
the
primers
(P1, P2, and P3) extend and the direction of synthesis
during primer
amplification
129, 30, 351. (b) Sequences
of the primate
CREs and nonprimate CRE homologs.
Numbers
indicate
nucleotide
position
with respect to
the transcription
start site and capital letters denote
nucleotide
differences
relative to the human
gene (P. Chimp = pygmy
chimpanzee).
Reproduced
with permission
from Fenstermaker
et al. 1351.
234
NILSON
The Horse a-Subunit
Despite the Absence
In addition
to
homolog
contains
tive GREs of cattle,
horse
GRE homolog
ET AL.
Gene Is Expressed
in Placenta
of a Functional
CRE
a few other
changes,
the same
C/T transition
sheep,
an
pigs
fails to displace
genes
the
CREB
GRE. This suggests
do not compensate
restore
GREB binding
activity
the horse
GRE homolog
fails
whether
the
horse
(Fig.
Each
of these
into
human
from
further
that the horse
a
protein,
even when
tracts
URE.
that
binds
specifically
to the
function
ilar
human
to the
extracts
whether
a GRE, we conclude
that if the horse
a GRE homolog
binds
a protein
unique
to horse
placenta,
this protein
must
be
quite
different
from the CREB family
of proteins
found
in
rat brain
[23] and liver [14], human
placenta
[14,22],
and
placenta-specific
To test
this
vectors
was
a series
of
of the GRE
a-subunit
transfected
evidence
nuclear
to
to
3).
The horse
a-subunit
gene
(Fig. 4a), suggesting
that this
a protein
could
choriocarcinoma
cells. These
results
indicated
that
and rhesus
GRE are active whereas
the GRE homologs
horse,
sheep,
and pig are inactive.
This provides
bind any nuclear
protein
when
incubated
with choriocarcinoma
cell extracts
or with extracts
prepared
from
fetal
equine
kidney
cells (FEK) (data
not shown).
Since FEK excontain
GRE homolog
if linked
to a functional
human
URE, we made
vectors
containing
a human
URE linked
to each
homologs
isolated
from
the various
mammalian
horse
a GRE
as do the inac-
(Fig. 2b). Similarly,
binding
of human
protein
[22] from the human
a-subunit
that these
other
nucleotide
differences
for the C/T transition
and
the horse
GRE. In addition,
the
determine
GRE is incapable
of binding
linked
to a functional
URE.
also contains
a URE homolog
sequence
binds
a protein
simprotein
possibility
a
that
indirectly,
binds
we
from
human
choriocarcinoma
the horse
URE can bind the
the
prepared
cells
protein
human
nuclear
to determine
that binds
to
a radioactive
human
URE sequence.
As shown
in Figure
4b,
gel-mobility
shift analysis
indicates
that the radioactive
human URE binds
to at least three
different
proteins
or pro-
FEK.
Cooperative
binding
occurs
between
proteins
that bind
to the URE and GRE of the human
a-subunit
gene
[15]. To
tein complexes
as distinguished
molecular
weights
(bands
1,2,
by
and
3).
differences
Bands
in
1 and
native
3 are
pSVI
I
I
I
____
I-i
41--AT
ATAAT
0
J-cAMP
AT
+cAMP
P
I
0
-
10
.I
I
20
30
40
CAT
FIG.
3.
ActIvity
of the
CPE4Ike
sequences
found
In the
proximal
promoter.regulatory
region
‘
I
of several
50
60
I
“150
300
Activity
mammalian
a-subunit
genes. Construction
of
the pSV1 vector (pXSV1CAT)
has been described
previously
I0l.
Polymarase
chain reactions
(29, 351 wIth primers
specific for the URE and TATA box of
the human a-subunit
gene (P1 and P2, FIg. 2a( were used to amplify
regions containing
the CRE or CRE-like
homologs
(C) from genomic
DNA of humans
(H, hatched
bars), rhesus monkeys
(R, vertical
bars), horses (E, horizontal
bar.), sheep (0, backhatched bars), and pigs (P, shaded). After IsolatIon and
purification,
the amplified
DNA fragments
were cloned Into the Xba I site of the parent pSV1 vector (351. To ensure that the SV 40 early promoter
directed
transcription
of the CAT gene, the PCR DNA fragments
were cloned In the opposite
orientation
relative
to the TATA box of the human
a-subunit
gene
which
Is present
In each of the amplified
DNA5. Call culture conditions,
transfection,
and CAMP
treatments were performed as described previously 1101.
All CAT activity
v&uea ware within the ((near range of the assay (27); values are expressed as percent
conversion
of substrate,
per microgram
protein,
per hour, relative to the parent pSV1 vector. Each value represents
the mean plu, SEM of 3 Independently
transfected
plates. Reproduced
with permission
from Fensterrnaker
at al. (351.
a-SUBUNIT
GENE
EXPRESSION
IN PRIMATE
HORSE
AND
235
PLACENTA
a
-147
-201
Human
cacctgaaaatggctccaaac-aaaaatgacctaagggttgaaacaagataagatc
Equine
cGcctgaaaatggctcaaaacaaaaaatgatctaagAgttgaaacaagataagatc
Bovine
caTctgaaaatggctcaaaacaaaaaatAatctaagggctgaaacaagataagatA
b.
hU
eU
II
Competitor
50*
-
100*
250*
500x
MSV
‘l8
500*
500*
I
00*
50*
250*
500*
2
3 -
URE.
FIG. 4. The horse URE binds the same nuclear protein(s)
in human
(a) Comparison
of the horse,
cattle and human
URE sequences.
choriocarcinoma
Numbers
indicate
spect to the transcription
start site of the human
a-subunit
gene and capital
letters
relative
to the human
gene. (b) Gel mobility
shift assay of nuclear extracts
prepared
cells using hU as the radioactive
probe. Lane 1, no competitor;
Lanes 2-5, increasing
competitor;
Lanes 6-9, increasing
molar excess of eU competitor;
Lanes 10-11,
500x
competitor
(MSV = CCAAT-box
sequence;
a18 = a-subunit
CRE 110, 341). Reproduced
maker et al. 1351.
sequence-specific
because
increasing
radioactive
human
URE
radioactive
human
URE.
displaces
plexes
the
equine
URE
when
binds
protein
a 500-fold
irig elements
were
Nonradioactive
sequence
same
excess
equine
human
Although
URE
to the
by the
lack
molar
of two
different
added
to the
binding
reaction
a-subunit
also
expressed
human
of competi(the
If the
of the
URE to comless efficient,
specifically
excess
of non-
binding
as evidenced
box from
MSV [34], and
gether,
these
data indicate
recognize
the
choriocarcinoma
molar
displaces
binding
of the radioactive
1 and 3, but less efficiently.
URE-binding
tion
efficiently
After
ment
fer
CCAAT
moter,
sequence-specific
protein(s)
in human
cells, but with different
affinities.
denote
nucleotide
differences
from human
choriocarcinoma
molar excess of unlabeled
hU
molar excess of heterologous
with permission
from Fenster-
promoter-regulatory
lacks a functional
gene
in placenta?
There
radiation
of oddand
binding
protein
may
the URE now functions
cz-act-
human
a GRE [10]).
Taken
tothat both horse
and human
UREs
proximal
cells that binds to the human
nucleotide
position
with re-
like
the
GRE.
URE-binding
If true,
unmasks
with
another
in horse
activity
may
a variety
cis-acting
is the
horse
gene
are at least three
possibilities.
even-toed
ungulates,
the URE-
the
horse
expression
protein
interacting
Thus,
only
of the
why
have evolved
independently
such
without
the aid of an accessory
placenta-specific
but
region
GRE, then
URE alone
to
placental
a
cells.
should
heterologous
that
eleconpro-
Alternatively,
the
be promiscuous
and capable of
of different
DNA-binding
proteins.
element
of the horse
may
have
emerged
URE. Finally, a URE
may
that
exist
NILSON
236
in the horse
gene,
but this element
in placenta-specific expression.
may
not be involved
If so, another
element
ET AL.
8. Fiddes
JC, Talinadge
human
must
9. Naylor
provide that function. We
possibilities.
are currently testing each of these
BJ. Bokar
lation
of the
URE
A functional
centa-specific
Expression
sory
to unmask
protein.
gene
centa
clearly
of the bovine
ates a functional
that
promoter
confers
and
this
for
study
cells.
play
ies [18].
Murine
comes
role
placenta
our
contains
crea-
a protein
mice
stud-
binds
spe-
that
suggests
portant
for
that
structural
in
tion
of the
unit
gene
quired
the
of other
placenta-specific
or
in conjunction
element/trans-acting
factor
JP,
and
comments
(ed),
on
Chorionic
2. Goodwin
level
of transcriptional
glvcoprotein
four
Moncman
sequence
3. Fiddes
a
21.
JA,
1981:
256:5121-6127.
Imura
6. Gharib
H (ed),
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and
The
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7. Wurzel
JM, Curabla
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1983:
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1990:
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