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Institute of Reproduction and Development (R.A.J., B.C., M.R., G.P.R.), Monash Medical Centre, Clayton, Victoria, 3168, Australia; School of Biological and Molecular Sciences (N.P.G.), Oxford Brooks University, Headington, Oxford, OX3 OBP, United Kingdom; and AgResearch (K.P.M.), Wallaceville Animal Research Centre, Upper Hutt, New Zealand
Address all correspondence and requests for reprints to: Dr. G. P. Risbridger, Institute of Reproduction and Development, Monash Medical Centre, Level 3, Block E, 246 Clayton Road, Clayton, Victoria, Australia, 3168. E-mail: gail.risbridger{at}med.monash.edu.au
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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-, ßA-, and ßB- subunits during ovine
testicular development from days 40–135 of gestation. Localization of
inhibin ßA- and ßB-subunit messenger RNAs
was confirmed by in situ hybridization.
The results showed that there was differential localization of inhibin
-, ßA-, and ßB-subunits to specific
cells in the ovine fetal testis from 40 days of gestation. All three
inhibin subunits were present in Sertoli cells throughout gestation,
whereas the rete epithelium and gonocytes did not express inhibin
-subunit. These data suggest that the fetal Sertoli cells have the
capacity to produce all forms of inhibins and activins,
i.e. inhibin A and B, and activins A, AB, and B, whereas
the rete testis epithelial cells can only synthesize activin A. In the
interstitium, the fetal Leydig cells expressed all three inhibin
subunits, but this was restricted to the period between 40 and 90 days
of gestation. Thereafter, inhibin -subunit immunoreactivity was not
observed in fetal Leydig cells, which suggests that only activin
ligands are produced by Leydig cells during late gestation.
Collectively, the data demonstrate that fetal ovine testes have the potential to produce the full repertoire of inhibins and activins from very early in testicular differentiation. The distinct and restricted localization of the various subunits to specific cells suggests that specific dimeric proteins have particular roles in the development and function of the fetal testis.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and ß
(ßA and ßB), linked by disulfide bonds (2).
These subunits combine to form inhibin A (ßA), inhibin
B (ßB), activin A (ßAßA),
activin AB (ßAßB), and activin B
(ßBßB). Inhibin subunits have been shown to act within the gonads as paracrine factors and have previously been detected in fetal testes of many species including human (3, 4, 5), monkey (4), rat (6, 7, 8), and bovine (9). It appears that the localization of inhibin subunits is variable between species and that the localization may vary during gonadal development, but both epithelial and interstitial cells have the ability to produce inhibin subunits.
In vivo and in vitro manipulations with inhibin, FSH, LH, and hCG demonstrated by an active FSH-inhibin feedback system have shown that intragonadal communications are functional during late intrauterine fetal development (4, 10, 11, 12). Administration of exogenous FSH to the ovine fetus increased production of inhibin as measured by a pituitary cell bioassay (10) and, conversely, administration of inhibin suppressed the plasma concentrations of immunoreactive FSH (11). Immunoreactive and bioactive inhibin were detected in the ovine fetus from 46 days of gestation and increased throughout gestation (12).
While Wongprasartsuk and colleagues (12) detected immunoreactive and
bioactive inhibin in the ovine fetus from 46–110 days of gestation,
studies by Thomas and co-workers (13) failed to localize inhibin
-subunit protein until 100 days of gestation, although the messenger
RNA (mRNA) was expressed from the earliest age examined (70 days of
gestation). Dimeric inhibins had previously been detected in the fetal
ovine testis from very early in gestation. It is therefore surprising
that inhibin -subunit protein could not be localized until late
gestation. Inhibin ßA-subunit localization has been
examined in fetal ovine testes (13) but was not detected at any stage
of gestation. Inhibin ßB-subunit localization has not
previously been examined. If bioactive dimeric inhibins and activins
are produced throughout testicular development, it is essential to
demonstrate the presence of these subunits during gestation.
Therefore, this study examined the expression and localization of
inhibin subunits throughout ovine testicular development by
immunohistochemistry using highly specific monoclonal antibodies for
-, ßA-, and ßB-subunit proteins and by
in situ hybridization using digoxygenin (DIG)-labeled
riboprobes for inhibin ßA and ßB mRNA. The
localization of the inhibin subunits enabled us to infer which inhibin
and/or activin ligands are produced by each cell type in the developing
ovine testis.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Male fetuses were recovered from pregnant Romney ewes with known single insemination dates at days 40, 55, 75, 90, 100, 120, and 135 of gestation (term = 145 days). Fetuses were recovered after a barbituate overdose (10 mg Euthatal iv) was given to their mothers (14). Testes (and mesonephroi at days 40 and 55 only) were dissected from five animals at each age and weighed to confirm fetal age. Testes were fixed in 4% paraformaldehyde overnight and processed to paraffin. Sections (5 µm) were cut and dried onto Esco Superfrost Plus-coated slides (Biolab Scientific, Australia and New Zealand) and used for immunohistochemistry or in situ hybridization.
Antibodies
To detect inhibin -subunit protein, monoclonal antibodies
(clone 173/29) raised to a synthetic peptide corresponding to amino
acids 1–32 of the N terminus of human inhibin -subunit were used at
4.5 µg/ml. These antibodies have previously been used for
immunohistochemistry (15). There is 85% amino acid homology in this
region between human and ovine inhibin -subunits. To detect inhibin
ß-subunits, monoclonal antibodies for ßA (E4) and
ßB (C5) raised against synthetic peptides corresponding
to amino acids 82–114 of human ßA- or
ßB-subunits were used at 2 µg/ml and 50 µg/ml,
respectively. The amino acid sequences of ovine inhibin
ßA- and ßB-subunits are identical to these
peptides. These antibodies have been used previously to measure inhibin
A and inhibin B in enzyme-linked immunosorbent assays (16, 17). The C5
antibody was shown to have 1% cross-reactivity with
ßA-subunit in these assays (18); therefore, before
immunolocalization of ßB-subunit, sections were incubated
with an excess of E4 antibody (20 µg/ml) for 2 h at 4 C to
occupy ßA-epitopes in the tissue. Inhibin
ßB-subunits were then detected by incubation with a
biotinylated form of the C5 antibody.
Antiserum against 3ß-hydroxysteroid dehydrogenase (3ßHSD), a marker of Leydig cells, was used to differentiate fetal Leydig cells from other interstitial cells. Polyclonal rabbit antiovine 3ßHSD antiserum was a kind gift from Professor I. J. Mason (Department of Clinical Biochemistry, University of Edinborough, UK) and was used at 12.5 µg/ml for immunofluorescence.
Control sections were incubated with either mouse IgG/IgM (Zymed Laboratories, Inc., San Francisco, CA) or normal rabbit serum
(Sigma Chemical Co., St Louis, MO) instead of primary
antibodies. Specificity of clone 173/29, E4, and C5 antibodies was
confirmed by preabsorption with 10x excess inhibin -,
ßA-, and ßB-subunits, respectively,
overnight at 4 C. The mixture was then centrifuged at 12,000 rpm before
incubation on tissue sections.
Immunohistochemistry
Indirect avidin-biotin-enhanced horseradish peroxidase
immunohistochemistry was used to localize inhibin -,
ßA-, and ßB-subunit proteins in testes from
at least three animals at each age. Sections were dewaxed, rehydrated
in graded alcohols, and placed in Target Retrieval Solution (Dako Corp., Carpinteria, CA). Antigenic sites were exposed by heating
to 90 C in a 1350-watt microwave, maintained for 5 min at 30% power,
and allowed to cool for 20 min. Sections were then treated with 6%
(vol/vol) hydrogen peroxide for 30 min, permeabilized with 0.2% Triton
X-100 for 10 min, and incubated with CAS block (Zymed Laboratories, Inc.) for 30 min at room temperature to block
nonspecific binding.
Sections were then incubated with primary antibodies overnight at 4 C
(clone 173/29), 2 h at 4 C (E4), or 2 h at room temperature
(biotinylated C5 after blocking of ßA-subunit sites).
After washing in PBS, the - and ßA-sections only were
incubated in biotinylated goat antimouse IgG (Vector Laboratories, Inc., Burlingame, CA) at 7.5 µg/ml for 1 h
at room temperature. After washing in PBS, all sections were then
incubated for 1 h with Vectastain Elite ABC kit
(Vector Laboratories, Inc.) and color reacted with
3,3'-diaminobenzidine tetrahydrochloride (Liquid substrate kit;
Zymed Laboratories, Inc.). The reactions were stopped in
water and sections were counterstained with Mayer’s hematoxylin,
dehydrated, cleared, and mounted.
Double immunofluorescence
Double immunofluorescence was used to determine whether any
interstitial staining was localized to fetal Leydig cells. Tissue
sections were dewaxed, rehydrated, subjected to antigen retrieval, and
permeabilized as described above. To block nonspecific binding,
sections were treated with CAS block (Zymed Laboratories, Inc.) and 10% normal goat serum (NGS) for 30 min at room
temperature. Sections were then incubated with primary antibodies
diluted in 10% NGS as described above. After washing with PBS, the
- and ßA-subunits were detected by incubation with
fluorescein isothiocyanate-conjugated goat antimouse IgG (Zymed Laboratories, Inc.) at 3.75 µg/ml in 10% NGS, and
ßB-subunits were detected by incubation with fluorescein
isothiocyanate-conjugated streptavidin (Vector Laboratories, Inc.) at 40 µg/ml in 10% NGS, both for 1 h at room
temperature in the dark. To detect fetal Leydig cells, sections were
then incubated in CAS block and 10% NGS, followed by incubation with
anti-3ßHSD antiserum in 10% NGS for 1 h at room temperature.
After washing with PBS, sections were incubated with CY3- conjugated
goat antirabbit IgG (Zymed Laboratories, Inc.) at 2.5
µg/ml in 10% NGS for 1 h at room temperature in the dark,
mounted in fluorescent mounting medium (Dako Corp.), and
stored at 4 C. Immunofluorescence was observed with a BX50 microscope
(Olympus Corp., Lake Success, NY) fitted with fluorescence
optics for light microscopy.
cRNA probes
DIG-labeled riboprobes were used in nonradioactive in
situ hybridization to localize mRNAs of inhibin ßA-
and ßB-subunits. Rat inhibin ßA cDNA was
cloned into pGEM-4Z (370-bp fragment; Ref. 19). Antisense and sense
cRNA probes were transcribed using T7 and SP6 RNA polymerases from
plasmids linearized with EcoRI and HindIII
restriction endonucleases, respectively. There is 89% homology between
ovine and rat inhibin ßA-subunit cDNA sequences. Human
inhibin ßB cDNA was cloned into pGEM-3Z (390-bp fragment;
Ref. 20). Antisense and sense cRNA probes were transcribed using T7 and
SP6 RNA polymerases from plasmids linearized with BamHI and
SmaI restriction endonucleases, respectively. There is 90%
homology between ovine and human inhibin ßB-subunit cDNA
sequences. In vitro transcription of DIG-labeled cRNA was
performed using a riboprobe labeling kit (Boehringer Mannheim, Indianapolis, IN). The concentration of DIG-labeled
cRNA probes was determined by comparison to a DIG-labeled RNA control
using dot blot analysis (data not shown).
In situ hybridization
In situ hybridization was performed as described
previously (21). Briefly, sections were dewaxed, rehydrated, treated
with 0.2 M HCl (for ßB riboprobes), digested
with 10 µg/ml proteinase K (Boehringer Mannheim) for 30
min at 37 C, treated with 0.2% glycine in PBS (for ßB
riboprobes), or postfixed in 4% paraformaldehyde in PBS (for
ßA riboprobes), and treated with 0.25% acetic anhydride.
Sections were prehybridized [in 3x saline sodium citrate (SSC; Ref.
22), 1x Denhardt’s solution (22), 50% deionized formamide, 66
mM phosphate buffer, pH 8, 100 µg/ml herring sperm DNA,
and 100 µg/ml transfer RNA] at 42 C for 30 min.
Riboprobes were diluted to 200 ng/ml in hybridization buffer (prehybridization solution plus 10% dextran sulfate), denatured at 65 C for 10 min, and then hybridized overnight at 42 C under coverslips in a humidified box. After hybridization, sections were washed in 2x SSC at room temperature, 2x SSC at 42 C, 1x SSC at 42 C, and 0.1x SSC at 42 C for 15 min each.
The tissue sections were briefly washed in buffer 1 (0.1 M maleic acid, 0.15 M sodium chloride, pH 7.5), incubated with blocking buffer (1% skim milk powder in buffer 1) for 30 min at room temperature followed by alkaline phosphatase-conjugated goat anti-DIG IgG (1:1000, Boehringer Mannheim) for 1 h. After washing in buffer 1, riboprobes were visualized using 5-bromo-4-chloro-3-indolyl phosphate and nitroblue tetrazolium salt (NBT/BCIP one-step, Pierce Chemical Co., Rockford, IL). The reaction was stopped in water, and sections were permanently mounted with GVA histomount (Zymed Laboratories, Inc.).
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-subunit. Immunostaining for inhibin -subunit
protein was observed in the seminiferous epithelium from 40–135 days
of gestation [Fig. 1
, A–C, E–G, I–K,
M–O, Q–S (day 135 not shown)] and was localized to Sertoli cells
(Fig. 1, C, G, K, O, and S). In contrast to the seminiferous
epithelium, the epithelial cells of the rete testis did not exhibit
inhibin -subunit protein at any age examined (Fig. 1, A, E, I, J, M,
N, Q, and R). No immunoreactivity was detected for the inhibin
-subunit in gonocytes at any gestational age (Fig. 1, C, G, K, O,
and S).
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-subunit (Fig. 1
, B and C), but with
advancing gestational age this intensity decreased (Fig. 1, K and O),
until 100 and 120 (Fig. 1S) days of gestation, at which time inhibin
-subunit protein was no longer detected. No immunostaining was
observed in any of the controls used for inhibin -subunit (Fig. 1, D, H, L, P, and T). The presence of inhibin -subunit
immunoreactivity in Leydig cells was confirmed by colocalization of
inhibin - subunit and 3ßHSD immunofluorescence at 55 days of
gestation (Fig. 2A). Leydig cells were
still present at 90 days of gestation, but were not double labeled with
inhibin -subunit (Fig. 2B).
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, A–H (day 135 not shown)] similar to
inhibin -subunit. Sertoli cells were immunoreactive for inhibin
ßB-subunit at all ages (Fig. 3, B, D, F, and H) and could
be distinguished from the epithelial cells of the rete testis, which
were not immunoreactive (Fig. 3, A, C, E, and G). Similarly to inhibin
-subunit, the gonocytes did not exhibit inhibin
ßB-subunit protein at any age examined (Fig. 3, B, D, F,
and H). Leydig cells showed immunoreactivity for the inhibin
ßB-subunit (Fig. 3, B, D, and F) throughout gestation.
Migrating Leydig cells were also immunoreactive (Fig. 3E). Preabsorbed
controls were negative at all ages of gestation (Fig. 3, I and J). The
localization of inhibin ßB-subunit immunoreactivity to
fetal Leydig cells was confirmed by double immunofluorescence with
3ßHSD (Fig. 2, C and D).
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). Sertoli cells and Leydig
cells contained mRNA for inhibin ßB-subunit whereas
gonocytes did not (Fig. 3K). Sense controls were negative (Fig. 3L).
Inhibin ßA-subunit.Inhibin
ßA-subunit protein was localized to Sertoli cells of the
seminiferous tubules at all ages examined from 40–135 days of
gestation [Fig. 3, M–T (day 135 not shown)]. In contrast to inhibin
- and ßB-subunits, inhibin ßA was also
detected in the epithelium of the rete testis (Fig. 3, M, O, Q, and S).
Variable immunoreactivity was observed in gonocytes (Fig. 3, P, R, and
T) of all animals examined. This variability in immunostaining was not
dependent on cell morphology, location within the tubule, nuclear
appearance, or age of animal. Fetal Leydig cells were immunoreactive
for inhibin ßA-subunit protein throughout gestation (Fig. 3, N, P, and T). Preabsorbed controls were negative (Fig. 3, U and V).
Inhibin ßA-subunit protein was colocalized with 3ßHSD
(Fig. 2, E and F), confirming the presence of inhibin
ßA-subunit in fetal Leydig cells.
Expression of inhibin ßA-subunit mRNA confirmed the
pattern of immunoreactivity in the fetal ovine testis at 90 days of
gestation. Expression was observed in both interstitial and
seminiferous tubule compartments (Fig. 3W) as well as the rete testis
(data not shown). Sertoli cells and Leydig cells contained mRNA for
inhibin ßA-subunit that was also expressed in gonocytes
at 90 days of gestation (Fig. 3W). Sense controls were negative (Fig. 3X).
Summary of inhibin subunits in the fetal ovine testis
A summary of immunoreactivity for all inhibin subunits is detailed
in Table 1. All inhibin subunit proteins
were detected in the fetal ovine testis from 40 days of gestation.
Specifically, in the epithelium of the seminiferous tubules, Sertoli
cells contained inhibin -, ßA-, and ßB-
subunits, whereas gonocytes were negative for inhibin and
ßB and only contained variable localization for inhibin
ßA-subunit. The rete testis epithelium contained only
inhibin ßA-subunit. In the interstitium, fetal Leydig
cells contained inhibin -, ßA-, and
ßB-subunits; however, localization of inhibin -subunit
ceased during midgestation, whereas inhibin ßA and
ßB persisted into late gestation. The pattern of
immunoreactivity for each of the inhibin ßA- and
ßB-subunits was confirmed by localization of mRNA by
in situ hybridization in each of the specific cell
types.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-, ßA-, and ßB-subunits in
specific cells of the fetal ovine testis. The expression of inhibin
ßA and ßB mRNA described corresponds with
detectable inhibin ßA- and ßB-subunit
proteins. To synthesize dimeric inhibin or activin ligands, the
subunits must be localized to the same cell types. The differential
cellular localization of inhibin subunits from as early as 40 days of
gestation indicated that specific inhibins and activins may be
synthesized in different cells of the ovine fetal testis. As Sertoli cells expressed all three inhibin subunits, they have the capacity to synthesize all forms of inhibin and activin (namely, inhibin A or B and activin A, B, or AB), whereas the rete epithelium only produced inhibin ßA-subunit, and therefore can only produce activin A. In addition to morphological and functional criteria, the rete epithelium was clearly distinguished from the seminiferous epithelium based on the differential localization of these subunit proteins. The capacity of fetal Sertoli cells to produce inhibins and activins is consistent with the previous detection of bioactive and immunoreactive inhibin in the fetal ovine testes at 46 days of gestation (12) and suggests that inhibin and activin are early markers of Sertoli cell function. In the human male, inhibin B is the physiologically important regulator of FSH (18). The localization data suggested that fetal Sertoli cells produce inhibin B, although inhibin A may also be produced. Further studies are required to determine the relative levels of the inhibin A and B ligands in the fetal circulation to establish the physiological importance of these inhibins as regulators of FSH during gestation.
Gonocytes, in contrast to Sertoli cells, expressed only inhibin
ßA-subunit mRNA and protein. This implies that activin A
is the ligand of importance to this cell type. Activin A has been shown
to stimulate spermatogonial cell division in rat testes (23), and this
effect is opposed by inhibin (23, 24). If similar actions occur on
gonocytes, then the autocrine action of activin A may be antagonized by
the paracrine effect of inhibins. Gonocytes did not synthesize inhibin
- or ßB-subunits; therefore, any direct action of
inhibins and activins (other than activin A) on gonocytes must occur
through paracrine interactions with Sertoli cells. As the supply of
activin ligands is limited, very few comparisons have been made between
the effects of activin A, activin B, and activin AB.
Fetal Leydig cells expressed all three inhibin subunit proteins and
therefore had the capacity to produce all five known inhibin and
activin ligands. The production of inhibin by Leydig cells is
controversial. In this study, we have clearly shown by colocalization
with 3ßHSD that fetal Leydig cells express inhibin -subunit and
thus can synthesize both inhibin A or B. In the fetal, immature, and
adult testis, inhibin A and activin A have been shown to have opposing
roles in the regulation of Leydig cell steroidogenesis; this regulation
may be due to paracrine interactions with other cells or to an
autocrine pathway within Leydig cells. Although inhibin -,
ßA-, and ßB-subunits were detected in fetal
Leydig cells, inhibin -subunit immunoreactivity declined between 40
and 90 days of gestation and was not detectable at 90 days. Therefore,
from 90 days onward, fetal Leydig cells can no longer produce inhibins,
allowing activins, in addition to other growth factors, to then
modulate the cellular response to LH, which is consistent with the
decline in serum testosterone in late gestation (25).
Inhibins and activins are secretory proteins that can act as endocrine hormones and have paracrine effects on surrounding cells. The discrete localization of inhibin subunits described in the present study suggests that the dimeric proteins have more restricted functions in specific cells of the fetal testis. For example, Sertoli cells have the potential to synthesize all known inhibin and activin ligands, whereas gonocytes can only synthesize activin A. This restricted localization implies that activins produced by Sertoli cells, which are in intimate contact with gonocytes, may have different actions to gonocyte-derived activin.
Previous studies have localized inhibin subunits in fetal human (5),
rat (15), and ovine (13) testes. In the fetal rat testis, inhibin
-subunit was localized to Sertoli and Leydig cells from day 14.5 of
gestation, but in fetal ovine testes, Thomas and colleagues (13) were
unable to detect inhibin - subunit protein until 100 days of
gestation. Our results report the detection of inhibin -subunit from
day 40 of gestation in the fetal ovine testes. Inhibin
ßA-subunit was not detected in fetal rat (15) or ovine
(13) testes, but our study reports the detection of inhibin
ßA-subunit protein and mRNA in fetal ovine testes
throughout gestation. In fetal human testis, inhibin ßA
subunit mRNA has been detected in interstitial cells (5), suggesting
that the differences with other studies may be due to sensitivity of
detection methods. Inhibin ßB-subunit expression has not
previously been examined in fetal ovine testes; however, in fetal human
(5) and rat (15) testes, the localization was similar to that reported
in the present study on fetal ovine testes.
Although it is known that there is bioactive and immunoreactive inhibin detectable in the adult ovine circulation (26), the specific localization of the inhibin subunits in the adult ovine testis has not been reported previously. In other species, inhibin subunit proteins have been localized to the seminiferous tubules and Leydig cells in adult testes of rats (15, 27), humans (28), and monkeys (28, 29). In these studies, inhibin ßA-subunit is present in the adult testis and has been localized to developing germ cells, as well as Sertoli and Leydig cells. These data are similar to those reported in this study using fetal ovine testes.
No studies to date have examined the localization of the activin receptors in fetal or adult ovine testes, although activin receptors are present in fetal rat seminiferous tubules, including gonocytes (7). For activin A to have paracrine or autocrine actions, these must be mediated by activin receptors. There are several ways in which to regulate activin ligand access to the receptor. Follistatin is an activin binding protein and, in other tissues, can neutralize the bioactivity of activin. If it is present in the fetal testis, it may play a significant role in regulating the bioactivity of activin. Follistatin has not been detected in fetal rat testes using in situ hybridization or immunohistochemistry (7, 15). This is surprising as follistatin protein has been detected by immunoassay in fetal ovine testicular extracts (12). Recently, follistatin mRNA has been detected in seminiferous tubules and intersitial cells of fetal human testes (5). These conflicting data may reflect species differences or may be due to low levels of follistatin expression.
Alternatively, activin ligands may be antagonized by novel activin
subunits. Additional activin subunits have been cloned, which give rise
to activin ßC- (30), ßD- (31), and
ßE-ligands (32). It is not known whether these subunits
can dimerize with inhibin -, ßA-, or
ßB-subunits to result in biologically active
heterodimeric proteins. Homodimers of ßD and
ßE have mesoderm-inducing actions (31), but the action of
ßC is unknown (30). ßC-subunit has been
shown to antagonize the actions of ßA-subunit in the
liver (31), and localization of ßC, ßD, and
ßE in the fetal testis may implicate these additional
subunits in activin action and testicular development.
In conclusion, we have shown that inhibin -, ßA-, and
ßB-subunits are expressed in the fetal testis and have
distinct cellular localizations. Our results suggest that inhibins and
activins may be very early markers of Sertoli cell function. The
production of inhibin A or B may contribute to the feedback regulation
of the hypothalamic-pituitary-gonadal axis, which is known to be active
by midgestation (10, 11). The restricted expression of inhibin
ßA -subunit in gonocytes implicates activin A in the
development and maintenance of germ cells in the fetal testis. Temporal
regulation of inhibin -subunit expression in fetal Leydig cells
suggests that inhibins and activins are involved in early Leydig cell
function, and that a loss of inhibin from midgestation may be important
for regulation of Leydig cell steroidogenesis in the fetal sheep
testis.
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Acknowledgments |
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Footnotes |
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Received August 7, 1998.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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- and inhibin ßA-subunits in
the fetal sheep testis. J Endocrinol 145:35–42[Abstract]
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) was intense during early gestation (C and G) but
decreased as development proceeded (K and O), and by 120 days of
gestation, no inhibin 
