Endocrinology Vol. 140, No. 4 1807-1814
Copyright © 1999 by The Endocrine Society
Regulation of Androgen Receptor Messenger Ribonucleic Acid Expression in the Developing Rat Forebrain1
Michael D. McAbee2 and
Lydia L. DonCarlos
Program in Neuroscience (M.D.M.) and the Department of Cell
Biology, Neurobiology, and Anatomy (L.L.D.C.), Stritch School of
Medicine, Loyola University of Chicago, Maywood, Illinois 60153
Address all correspondence and requests for reprints to: Dr. Lydia L. DonCarlos, Department of Cell Biology, Neurobiology, and Anatomy, Stritch School of Medicine, Loyola University of Chicago, 2160 South First Avenue, Maywood, Illinois 60153. E-mail: ldoncar{at}luc.edu
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Abstract
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By postnatal day 10 (PND-10), males express more androgen receptor (AR)
messenger RNA (mRNA) than females in the principal portion of the bed
nucleus of the stria terminalis (BSTpr) and medial preoptic area (MPO),
but not in the ventromedial hypothalamus. The development of these
region-specific sex differences in AR mRNA expression may be critical
for the organization of male-typical neural circuitry and may represent
the onset of sex differences in the sensitivity of the rat brain to the
actions of androgens. In this study, we used a 35S-labeled
riboprobe and in situ hybridization to address whether
postnatal testosterone exposure is important for the up-regulation of
AR mRNA content in the developing rat forebrain.
In the BSTpr and the MPO of PND-10 rats, males gonadectomized on PND-0
or PND-5 had lower levels of AR mRNA compared with intact or
sham-operated control males. Daily replacement of testosterone to
animals gonadectomized on PND-0 maintained AR mRNA content in the BSTpr
and the MPO at levels equal to those in intact males. In contrast,
there was no effect of gonadectomy or testosterone replacement on AR
mRNA expression in the ventromedial hypothalamus. Thus, the postnatal
hormonal environment may permit the development of region-specific sex
differences in AR mRNA.
Significant alterations in AR mRNA expression in the BSTpr and MPO in
PND-10 male rats were induced by gonadectomy as late as PND-8. Males
gonadectomized on PND-8 had levels of AR mRNA significantly lower than
those in intact males, but significantly higher than those in intact
females. Further, when animals were gonadectomized on PND-0 and given
testosterone on PND-8 and PND-9, levels of AR mRNA were also
intermediate between those found in intact males and intact females.
The exact time course for transcriptional regulation of AR mRNA in the
developing rat brain is unknown. However, others have shown significant
regulation of AR mRNA within hours of hormone treatment, so that 2 days
of hormone withdrawal or replacement are probably sufficient to achieve
new steady state levels of message. Moreover, sexually dimorphic
neuronal loss has been documented to peak in hypothalamic cell groups
during the first postnatal week. Thus, it is likely that changes in the
number of AR mRNA-expressing cells as well as the amount of AR mRNA
expression per cell are responsible for the development of male-typical
AR mRNA content.
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Introduction
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EXPOSURE of the rodent nervous system to
the male gonadal hormone testosterone during the perinatal period
permanently masculinizes numerous behavioral, physiological, and
neuroanatomical functions (1). During this period, testosterone may be
converted to either androgenic or estrogenic metabolites (2, 3).
Although there is abundant evidence that estrogen (4) and its receptor
(5) are critical for masculinization, other evidence suggests that
estrogen alone is not sufficient for complete sexual differentiation
and implicates androgen action in this process. For example, testicular
feminized rats, which are sensitive to estrogen but insensitive to
androgens, are not completely masculinized (6). Further, androgen
exposure during development is integral to the maturation of certain
social behaviors (7, 8, 9) and the complete expression of male sexual
behavior in adulthood (10, 11).
The impact of testosterone and its metabolites on the organization of
forebrain morphology and function is most dramatic during the
classically defined critical period from embryonic day 18 (ED-18) to
postnatal day 5 (PND-5) (12, 13), but sensitivity to the developmental
effects of testosterone extends beyond the first week of postnatal
development (14). We have recently demonstrated that androgen receptor
(AR) messenger RNA (mRNA) is present in the rat forebrain during this
critical period and that expression of AR mRNA increases with age (15).
This confirms that the receptor necessary for androgen-specific action
is actively transcribed during this period. Additionally, between PND-4
and PND-10, a region-specific sex difference in AR mRNA expression
develops in the principal bed nucleus of the stria terminalis (BSTpr)
and medial preoptic area (MPO), with males having higher AR mRNA levels
than females (15). This sex difference is not present in the lateral
septum, ventromedial hypothalamus (VMH), or arcuate nucleus (15). The
BSTpr and MPO are part of an integrated neural circuitry that controls
male sexual behavior in the adult rat (16). Numerous studies have shown
sex differences in the capacity of testosterone to induce male sexual
behaviors in the adult rat; for example, males exhibit a more complete
pattern of male sexual behavior than females in response to treatment
with exogenous testosterone (1). Therefore, sex differences in AR mRNA
in these areas may be indicative of sex differences in the sensitivity
of the developing rat brain to the actions of androgens.
During the perinatal period, circulating levels of testosterone are
higher in the male than in the female rat (17, 18). Further,
testosterone regulates AR expression in the BST and MPO of the adult
rat (19, 20). Thus, we hypothesized that the development of sex
differences in AR mRNA occurs as a result of exposure to testosterone
during the perinatal period. The potential regulation of AR expression
may represent a fundamental step in the cascade of events leading to
brain masculinization. In this study, we used an
35S-labeled riboprobe and in situ hybridization
to directly address whether postnatal testosterone exposure is
important for the regulation of AR mRNA content and to indirectly
determine whether testosterone regulates the number of AR
mRNA-expressing cells or the amount of AR mRNA per cell during this
process.
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Materials and Methods
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Animals
Timed pregnant Sprague-Dawley rats were obtained from
Zivic-Miller Laboratories, Inc. (Pittsburgh, PA). Animals
were housed separately in a controlled environment on a 12-h light,
12-h dark cycle (lights on from 0700–1900 h), with food and water
available ad libitum. On PND-0 (day of birth), each litter
was adjusted to five females and five males.
Before sacrifice, body weight and ano-genital distances were recorded.
All animals were anesthetized with ether and decapitated on PND-10.
Brains were quickly removed, rapidly frozen in powdered dry ice, and
stored at -70 C. Frozen sections were cut from the rostral forebrain
to the midbrain at a thickness of 16 µm and mounted on SuperFrost
Plus slides (Fisher Scientific International, Inc.,
Pittsburgh, PA). Slides were stored at -70 C until processing for
in situ hybridization.
Surgeries
Bilateral gonadectomies were performed on male rats on PND-0 or
PND-5 for Exp 1 and 2 and on PND-0 or PND-8 for Exp 3. Gonadectomies on
PND-0 were started more than 2 h after birth, which is after the
peak surge of neonatal testosterone. All animals were chilled on ice to
induce anesthesia. A small incision, approximately 1 mm long, was made
through the skin and abdominal wall just rostral and lateral to the
phallus. The testis was removed, and a single suture of 6.0 chromic gut
was used to close the incision. The surgery was repeated on the
opposite side. The incisions were covered with collodion to aid
healing. Control male rats underwent sham operations in which the
gonads were visualized but were not removed. Before being returned to
the dam, all pups were warmed under a heat lamp until a normal body
temperature and level of activity were achieved.
Testosterone treatments
Testosterone propionate (TP; 10 µg/0.1 cc in sesame oil) was
administered sc in the dorsum through a 20-gauge needle to decrease
resistance and ensure rapid administration of hormone. Control animals
received injections of sesame oil vehicle. A drop of collodion was
placed over the site of injection to prevent any leakage. All
treatments were made daily beginning on the day of gonadectomy and
continued through PND-9, the day before death. The site of
administration was rotated each day to avoid damage to the skin as well
as to maximize the uptake of testosterone. In those litters receiving
hormone treatment, all animals in a litter were given the same
substance (TP or oil) to ensure that excreted metabolites or leakage
from the injection site did not affect littermates.
Treatment groups
Exp 1 had six different treatment groups: intact males, intact
females, males gonadectomized on PND-0 (GDX-0), males gonadectomized on
PND-5 (GDX-5), males sham operated on PND-0 (sham-0), and males sham
operated on PND-5 (sham-5). Exp 2 had four different treatment groups:
intact males, intact females, GDX-0, and males gonadectomized on PND-0
and given testosterone replacement on PND-0 through PND-9 (GDX-0 +
TP-0–9). Exp 3 had five different treatment groups: intact males,
intact females, GDX-0, males gonadectomized on PND-8 (GDX-8), and males
gonadectomized on PND-0 and given testosterone on PND-8 and PND-9
(GDX-0 + TP-8,9). Each treatment group was comprised of animals from at
least three different litters.
In situ hybridization
In situ hybridization procedures were conducted as
previously described (15). AR mRNA was detected using a
35S-labeled complementary RNA probe transcribed from a rat
AR complementary DNA corresponding to nucleotides 3350–3840. The
complementary RNA probe was diluted with hybridization buffer to a
final activity of 1.5 x 107 cpm/ml. The tissue was
prepared for hybridization by acetylation, delipidation, and
dehydration. Each slide was hybridized with 100 µl hybridization
solution for 20 h at 60 C. After hybridization, slides were rinsed
in sodium chloride-sodium citrate (SSC), treated with ribonuclease, and
rinsed again to a final stringency of 0.1 x SSC at 60 C. After
the rinses, slides were dehydrated, allowed to air-dry, and apposed to
Hyperfilm Betamax (Amersham, Arlington Heights, IL) to
produce film autoradiograms for analysis.
Analysis
Analysis of the film autoradiograms was carried out using NIH
IMAGE analysis software (developed at the NIH available at
http://rsb.info.nih.gov/nih-image/) and a Macintosh IIci computer with
Scion videocard (Scion Corp., Walkersville, MD) attached to a Sony
video camera (Imaging Research, Inc., St. Catherines,
Canada). Three sections per animal were analyzed bilaterally per region
of interest. The analysis focused on two regions that were previously
shown to have a sex difference in AR mRNA on PND-10 (15): the BSTpr and
the MPO. The VMH, a region with no sex difference in AR mRNA expression
at PND-10, was also examined (15). The atlas of Swanson was used to aid
in the identification of cell group boundaries (21). Each cell group
was analyzed based on detectable signal as previously described (15).
The entire area of label was outlined regardless of signal intensity.
The average pixel value of the outlined region was measured and
expressed as a mean gray level. These mean gray levels represent a
semiquantitative index of steady state levels of AR mRNA.
To minimize the potential for variability due to interrun differences,
brain sections from an equivalent number of animals from each treatment
were processed in each hybridization run. In addition, to eliminate
differences due to nonspecific hybridization, five background measures
were taken from the caudate-putamen of each animal. The mean background
measure for each animal was subtracted from each individual mean gray
level to obtain a corrected gray value. As one-way ANOVA
(P 
0.05) demonstrated that average corrected gray
levels from left and right hemispheres were not different, values from
both hemispheres were combined to yield one mean corrected gray value
for each animal. The effects of treatment on mean corrected gray values
were analyzed by one-way ANOVA for each area, with planned
post-hoc tests (Fisher’s protected least significant
difference and Scheffe’s multiple comparison test). Differences were
considered significant at P 0.05. Individual
t tests, with P 0.01, were performed to
examine specific differences due to treatment. Body weight and
ano-genital distances were also analyzed for each experiment by one-way
ANOVA with planned post-hoc tests.
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Results
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Body weight and ano-genital distance
In each experiment, there was no effect of treatment on body
weight (Table 1
). Ano-genital distances
were significantly lower in intact females than in all other treatment
groups (P 0.01; Table 1). Gonadectomy had no effect
on ano-genital distance in any experiment.
Exp 1: does gonadectomy on PND-0 or PND-5 decrease AR mRNA content
in the developing male rat forebrain?
In this experiment, we asked whether postnatal exposure to
testicular hormones up-regulated AR mRNA content. AR mRNA expression
was examined in PND-10 male rats that had undergone gonadectomy on
either PND-0, after prenatal development, or PND-5, after the end of
the classically defined critical period (12). Specifically, the BSTpr
and MPO were examined because they were previously shown to express
sexually dimorphic AR mRNA content (15). The VMH was examined as a
control area that demonstrates no sex difference in AR mRNA expression
(15).
In the BSTpr, in agreement with our previous findings (15), intact
males expressed more AR mRNA than intact females on PND-10. Further,
gonadectomy on either PND-0 or PND-5 resulted in significantly lower
levels of AR mRNA compared with those in intact males
(P 0.01; Fig. 1). In
the MPO, as observed previously (15), males also expressed more AR mRNA
than intact females. In addition, AR mRNA expression was significantly
lower after gonadectomy (P 0.01; Fig. 2). Gonadectomy on PND-0 or PND-5 lowered
AR mRNA content in the BSTpr and MPO to levels not significantly
different from those in intact females. In contrast to the MPO and BST,
AR mRNA in the VMH, was not altered by gonadectomy (P
0.992; Fig. 3). AR mRNA expression in
sham-operated animals was not significantly different from that in
intact males in any area examined (data not shown). Thus, hormone
exposure from PND-5 through PND-10 is necessary to achieve male-typical
levels of AR mRNA in PND-10 males.
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Figure 1. The effect of postnatal gonadectomy on AR mRNA
expression in the BSTpr of PND-10 rats. The digitized images show
comparisons among intact males, intact females, and males
gonadectomized on PND-0 (GDX-0) or PND-5 (GDX-5). Semiquantitative
analysis of AR mRNA levels is represented in the graph. Each
column represents the mean gray level, and error
bars represent the SEM (n = 6
animals in each group). *, Different from intact male animals,
P 0.01.
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Figure 2. The effect of postnatal gonadectomy on AR mRNA
expression in the MPO of PND-10 rats. The digitized images show
comparisons among intact males, intact females, and males
gonadectomized on PND-0 (GDX-0) or PND-5 (GDX-5). Semiquantitative
analysis of AR mRNA levels is represented in the graph. Each
column represents the mean gray level, and error
bars represent the SEM (n = 6
animals in each group). *, Different from intact male animals,
P 0.01.
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Figure 3. The effect of postnatal gonadectomy on AR mRNA
expression in the VMH of PND-10 rats. The digitized images show
comparisons among intact males, intact females, and males
gonadectomized on PND-0 (GDX-0) or PND-5 (GDX-5). Semiquantitative
analysis of AR mRNA levels is represented in the graph. Each
column represents the mean gray level, and error
bars represent the SEM (n = 6
animals in each group).
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Exp 2: does treatment with exogenous testosterone after gonadectomy
sustain AR mRNA expression at intact male levels?
This experiment specifically addressed whether postnatal
testosterone exposure is sufficient for up-regulation of AR mRNA to
male-typical levels. In this experiment, male rats were gonadectomized
on PND-0 and received daily injections of TP (10 µg/day) on PND-0
through PND-9, with death on PND-10.
AR mRNA expression in males gonadectomized on PND-0 and treated with TP
was not significantly different from that in intact males in the BSTpr
or MPO (Figs. 4 and 5). In both areas,
levels of AR mRNA in gonadectomized animals given TP replacement were
significantly higher than those in intact females (BSTpr:
P 0.01; Fig. 4; MPO: P 0.01; Fig. 5). Further, levels of AR mRNA in males
gonadectomized on PND-0 given TP were significantly higher than those
in males gonadectomized on PND-0 that did not receive TP (BSTpr:
P 0.01; Fig. 4; MPO: P 0.01; Fig. 5). As in Exp 1, levels of AR mRNA in the VMH were not different
between intact males and intact females and were not affected by
gonadectomy or TP replacement after gonadectomy (Fig. 6). Thus, postnatal exposure to TP was
sufficient to produce male-like AR mRNA content in the developing BSTpr
and MPO and had no little or no effect on the expression of AR mRNA in
the VMH.
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Figure 4. The effect of TP treatment after neonatal
gonadectomy on AR mRNA expression in the BSTpr of PND-10 rats. The
digitized images show comparisons among intact males, intact females,
males gonadectomized on PND-0 (GDX-0), and males gonadectomized on
PND-0 that received TP treatment on PND-0 through PND-9 (GDX-0 + TP 0
to 9). Semiquantitative analysis of AR mRNA levels is represented in
the graph. Each column represents the mean gray level,
and error bars represent the SEM
(n = 6 animals in each group). *, Different from intact male
animals, P 0.01.
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Figure 5. The effect of TP treatment after neonatal
gonadectomy on AR mRNA expression in the MPO of PND-10 rats. The
digitized images show comparisons among intact males, intact females,
males gonadectomized on PND-0 (GDX-0), and males gonadectomized on
PND-0 that received TP treatment on PND-0 through PND-9 (GDX-0 + TP 0
to 9). Semiquantitative analysis of AR mRNA levels is represented in
the graph. Each column represents the mean gray level,
and error bars represent the SEM
(n = 6 animals in each group). *, Different from intact male
animals, P 0.01.
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Figure 6. The effect of TP treatment after neonatal
gonadectomy on AR mRNA expression in the VMH of PND-10 rats. The
digitized images show comparisons among intact males, intact females,
males gonadectomized on PND-0 (GDX-0), and males gonadectomized on
PND-0 that received TP on PND-0 through PND-9 (GDX-0 + TP 0 to 9).
Semiquantitative analysis of AR mRNA levels is represented in the
graph. Each column represents the mean gray level, and
error bars represent the SEM
(n = 6 animals in each group).
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Exp 3: does short-term gonadectomy or short-term replacement of
testosterone after gonadectomy alter AR mRNA expression?
This experiment addressed indirectly whether regional sex
differences in AR mRNA content and the potential regulation of AR mRNA
by testosterone are due to alterations in the number of AR
mRNA-expressing cells, the amount of AR mRNA per cell, or both. The
packing density of neurons in the regions of interest is too high
during development to permit direct cellular analysis. However, making
use of previous reports that the peak period of developmental cell
death in these areas is before PND-8 (22), and that a 2-day time course
provides ample time for hormone-dependent AR mRNA gene regulation (23),
two treatments were designed to address this question. First, male rats
underwent gonadectomy on PND-8, with death on PND-10. These rats would
be expected to have a male-typical number of neurons. Second, some
animals were gonadectomized on PND-0, followed by short-term treatment
with TP on PND-8 and PND-9 and death on PND-10. These animals would be
expected to have a female-typical number of neurons.
After gonadectomy on PND-8, AR mRNA expression was significantly lower
in the BSTpr (P 0.01; Fig. 7) and MPO (P 0.01;
Fig. 8) than that in intact males when AR
mRNA content was examined on PND-10. AR mRNA expression was
significantly higher in males gonadectomized on PND-8 than in intact
females or in males gonadectomized on PND-0 in BSTpr (P
0.01; Fig. 7) and MPO (P 0.01; Fig. 8). As levels
of AR mRNA were significantly reduced after gonadectomy on PND-8 but
remained significantly higher than those in males gonadectomized on
PND-0, it is likely that the production of male-like AR mRNA content in
the BSTpr and MPO was due to alterations in both the number of
AR-expressing cells and the amount of AR mRNA per cell.
In males gonadectomized on PND-0 and treated with TP on PND-8 and
PND-9, levels of AR mRNA expression in the BSTpr and MPO were
intermediate between levels observed in the intact males and intact
females (Figs. 7
and 8). AR mRNA expression in the BSTpr and MPO of
TP-treated animals was significantly higher than that in males that did
not receive TP treatment (Figs. 7 and 8). These results, similar to
those reported above, are indicative of changes in both the number of
AR mRNA-expressing cells and the amount of AR mRNA per cell in response
to short-term hormone replacement. As expected, AR mRNA expression in
the VMH was not altered 2 days after gonadectomy or after gonadectomy
with 2-day hormone replacement (Fig. 9).
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Figure 9. The effect of short term hormone manipulation on
AR mRNA expression in the VMH of PND-10 rats. The digitized images show
comparisons among intact males, intact females, males gonadectomized on
PND-8 (GDX-8), and males gonadectomized on PND-0 that received TP on
PND-8 and PND-9 (GDX-0 + TP-8,9). Semiquantitative analysis of AR mRNA
levels is represented in the graph. Each column
represents the mean gray level, and error bars represent
the SEM (n = 6 animals in each group).
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Discussion
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The first experiment of this study demonstrated that gonadectomy
on PND-0 or PND-5 decreased AR mRNA expression by PND-10 in a
region-specific manner. AR mRNA expression in the BSTpr and MPO was
significantly reduced in males after gonadectomy at either age. In
contrast, AR mRNA expression in the VMH was not altered in
gonadectomized males. These experiments confirm our previous reports of
region-specific sex differences and demonstrate that the pattern of
regulation of AR mRNA parallels the pattern of region-specific sex
differences (15).
In addition, the first experiment demonstrated that sex differences in
AR mRNA content in the developing rat forebrain are primarily dependent
on the postnatal hormonal environment. Prenatal hormone exposure is not
sufficient to produce male-typical levels of AR mRNA in these areas, as
gonadectomy on either PND-0 or PND-5 eliminated the sex difference in
AR mRNA expression exhibited on PND-10 in the MPO and BST.
In addition to confirming the effect of gonadectomy on PND-0, the
second experiment addressed the capacity of exogenous testosterone to
maintain male-like levels of AR mRNA expression after gonadectomy.
Replacement of testosterone to male rats gonadectomized on PND-0
sustained AR mRNA hybridization intensity at levels not significantly
different from those in intact males. However, testosterone may be
converted to estrogenic and androgenic metabolites, and both estrogen
and androgens regulate AR mRNA expression in the adult rat (20). Thus,
production of male-typical levels of AR mRNA may be due to androgenic
regulation, estrogenic regulation, or both. Moreover, regional
specificity of AR mRNA regulation in the neonatal brain may depend upon
the concerted actions of androgens and estrogens. This idea is
supported by studies demonstrating that aromatase levels in the BST and
MPO are among the highest of any forebrain region (19). Further,
colocalization studies in the rat and hamster BST and MPO also show a
high degree of AR and ER colocalization in the adult (24, 25).
Therefore, up-regulation of AR mRNA may require estrogenic metabolites
of testosterone and expression of the estrogen receptor, consistent
with our earlier hypothesis that one role of estrogen in the neonatal
brain is to enhance sensitivity to subsequent androgen exposure (15).
Experiments are underway to determine whether the development of sex
differences in AR mRNA content in the neonate are dependent upon
androgenic or estrogenic mechanisms.
As mentioned earlier, because of the high packing density of
neurons in the BSTpr and MPO during development, we are unable to
perform a direct cellular analysis to determine whether the regulation
of AR mRNA content by testosterone during the neonatal period is due to
alterations in the number of AR mRNA-expressing cells, the amount of AR
mRNA per cell, or both. Therefore, we have addressed this question
indirectly basing our experimental design and conclusions on the
results of previous studies showing that 1) the peak period of
developmental cell death in these areas is before PND-8 (22); 2) 2 days
provide ample time for hormone-dependent AR mRNA gene regulation (23);
and 3) in vitro, maximal regulation of AR mRNA by androgens
occurs 48–49 h after hormone addition (26, 27). In the third
experiment, males with presumably more cells and without testosterone
for 2 days (GDX-8) had more AR mRNA than females, but less AR mRNA than
intact males; perhaps the GDX-8 males did not approach the lower female
levels because they had more AR mRNA-expressing cells. Similarly, males
with presumably the same number of cells as females and receiving
testosterone replacement for 2 days (GDX-0 + TP-8,9) had more AR mRNA
than females but less than intact males. The GDX-0 + TP-8,9 males may
not have achieved intact male levels of AR mRNA because they had fewer
AR mRNA-expressing cells. Both sets of results from the third
experiment suggest that the development of sex differences in AR mRNA
content are dependent upon regulation by testosterone of both the
amount of AR mRNA per cell and the number of AR mRNA-expressing cells.
There are other possible explanations for these findings; the most
obvious is that 48 h of hormone depletion or replacement are
insufficient to maximally regulate AR mRNA content in vivo.
Additional experiments are in progress to determine the time course of
testosterone-dependent regulation of AR mRNA content.
Interestingly, in the adult rat, short term gonadectomy produces a
transient up-regulation of AR mRNA expression in the MPO and BST (20).
As, in contrast, our study demonstrates a rapid down-regulation of AR
mRNA after gonadectomy, the mechanism regulating AR gene transcription
may be different in the neonatal vs. the adult rat.
One explanation for a possible difference in the capacity of
androgens to regulate the AR during the perinatal period vs.
adulthood is that an integral factor is missing or has yet to develop
in the perinatal animal. Candidates for such a factor include
AR-associated proteins, transcription cofactors, and growth factors.
Examples of each of these have been shown to modify AR function.
Specifically, the ARA-70 protein increases the transcriptional
efficiency of the AR (30), whereas the presence of TFIIF alters the
trans-activation function and ultimately the transcriptional
capacity of the AR (31). In addition, recent studies have shown that
other proteins, including receptor-associated coactivator-3 (32) and
steroid receptor coactivator-1 (33), mediate the activation of nuclear
hormone receptors. Further, both platelet-derived growth factor and
transforming growth factor-ß have been shown to affect AR mRNA gene
expression in cultures of smooth muscle cells (34, 35). The absence
of each of these or other similar factors during the perinatal period
may result in inefficient AR-mediated transcription and may account for
putative differences in the regulation of AR mRNA expression between
the neonatal period and adulthood.
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Acknowledgments
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The authors thank Dr. R. J. Handa for providing the AR
complementary DNA template, Drs. R. J. Handa and K. J. Jones
for critical review of the manuscript, and Karen Schwenk for technical
assistance.
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Footnotes
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1 This work supported by NIMH Grant MH-48794 and NSF Grant
IBN-9604487. 
2 Present address: Department of Biology, University of Massachusetts,
Morrill Science Center, Amherst, Massachusetts 01003.
Received May 15, 1998.
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Abstract
Introduction
