| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Division of Endocrinology, Metabolism, and Molecular Medicine, Northwestern University Medical School, Chicago, Illinois 60611; and the Reproductive Endocrine Unit, Massachusetts General Hospital (P.A.S.), Boston, Massachusetts 02114
Address all correspondence and requests for reprints to: Jeffrey Weiss, Ph.D., Northwestern University, S217, 303 East Chicago Avenue, Chicago, Illinois 60611. E-mail: jeff-weiss{at}nwu.edu
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Although originally identified in the ovary, activin and follistatin have been detected in a variety of tissues (9, 10) and are abundantly expressed in the pituitary (11, 12, 13). The latter observation suggests that activin and follistatin could form an autocrine or paracrine loop to regulate FSH (14). This hypothesis is supported by in vitro experiments in which FSHß mRNA levels and FSH secretion decreased during exposure of rat pituitary cell cultures to activin-neutralizing antibodies (15). Recently, we demonstrated that endogenous follistatin suppresses activin-mediated production of FSH in the intact male pituitary (16). In these studies, pituitary follistatin was sensitive to the GnRH pulse frequency, suggesting that follistatin is also an important intermediary in the physiological control of FSH by GnRH.
In the female rat pituitary the physiological roles of activin and follistatin are potentially much greater. A precise pattern of FSH synthesis and release is required for appropriate folliculogenesis, and large changes in follistatin mRNA have been observed during the rat estrous cycle (17). There is also evidence that activin contributes to generation of the secondary FSH surge, which occurs independent of LH release and initiates follicular recruitment (18). The present studies were thus designed to determine whether changes in activin stimulation are responsible in whole or in part for the patterns of FSHß gene expression and FSH secretion observed during the rat estrous cycle and, if so, whether follistatin is involved in the control of activin at these times.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Perifusion medium and reagents were obtained from Life Technologies (Grand Island, NY) unless otherwise noted. Activin (lot 15365–23) was generously provided by Dr. Jennie Mather (Genentech, South San Francisco, CA). Follistatin (code B4384) was provided by the National Hormone and Pituitary Program, which is supported by the NICHHD (NIH), the NIDDK (NIH), and the USDA.
Pituitary dispersion and perifusion
On the day of an experiment, rats were killed, and anterior
pituitaries were immediately removed and diced into 15–20 pieces each.
Tissue fragments were enzymatically dispersed (19), and the cell
suspension was mixed with Bio-Gel P-2 (100 mg/column; Bio-Rad,
Hercules, CA) that had been prehydrated in saline for 2–4 h. One
anterior pituitary was dispersed per column, yielding about 1.8 x
106 cells. The cell/Bio-Gel mixture was incubated for
1 h at 37 C to permit attachment of the cells to the beads before
the columns were loaded. Columns were perifused overnight at a rate of
150 µl/min with RPMI 1640 medium containing 1% FBS. Experiments were
initiated the following morning after increasing the flow rate of RPMI
1640 to 250 µl/min. After an experiment, the contents of each column
was extracted in 1 ml guanidine thiocyanate for preparation of RNA
(20).
Quantification of FSHß and follistatin mRNA levels
FSHß and follistatin mRNA levels were assessed using
semiquantitative reverse transcription-PCR assays. Assay methods (16)
and primer sequences (17) were previously described. In brief, 1 µg
total RNA was reversed transcribed using random hexamer priming. A
linear dilution series was made from the resulting complementary DNA,
and individual dilutions were amplified in the presence of
[
-32P]deoxy-CTP using primers for FSHß or
follistatin as well as -tubulin as an internal control.
Amplification products were separated on acrylamide gels, quantitated
by autoradiography, and calculated as a ratio of FSHß or follistatin
to -tubulin, and the dilutions were then averaged for each
sample.
Immunoassays
Total follistatin was measured using a RIA that is insensitive
to the presence or absence of bound activin (21). Recombinant human
follistatin-288 (rhFS-288), used as the assay standard, was obtained
through the National Hormone and Pituitary Program. Rat serum, rat
corpus luteum, rat pituitary extracts, bovine follicular fluid, porcine
follicular fluid, human follicular fluid, and human pituitary extracts
(21) each diluted parallel to the rhFS-288 standards. Conditioned
medium from cells expressing the alternative 344-amino acid splice
variant of follistatin also generated response curves parallel to that
of the rhFS-288 assay standard. Intra- and interassay coefficients of
variation (CVs) were 8% and 11%, respectively. Serum activin A was
measured in a two-site enzyme-linked immunosorbant assay (ELISA) that
detects only activin that is not bound to follistatin. The ELISA
methods used were those previously described for human serum (22, 23),
except that the detection antibody was biotinylated to increase
sensitivity. Assay standards diluted linearly and in parallel when
measured in rat or human serum. Intra- and interassay CVs were each
less than 10%. LH and FSH were measured by RIA using reagents from the
National Pituitary Program. Reference preparations were FSH RP-2 and LH
RP-2. Intra- and interassay CVs were 4% and 11%, respectively, for LH
and 3% and 8% for FSH. Serum estradiol was measured using a kit from
Diagnostics Products Corp. (Los Angeles, CA), and progesterone was
measured using a kit from ICN (Costa Mesa, CA). Intra- and interassay
CVs were 3% and 8%, respectively, for estradiol and 7% and 13% for
progesterone.
Arterial infusions
Carotid arterial catheters were made by inserting the end of a
section of polyethylene tubing (PE-50, Becton Dickinson, Sparks, MD)
into a Tygon tubing connector (1/32 inch id; Norton Performance
Plastics, Akron, OH). Animals were lightly anesthetized with
methoxyflurane (Metofane, Pittman Moore, Mundelein, IL), a small
incision was made above the thymus gland, and the left carotid artery
was exposed. A small nick was made on the ventral surface of the
vessel, and the catheter was inserted and advanced cranially to provide
an infusion point proximal to the pituitary gland. The connector tubing
was tunneled sc, externalized at the nape of the neck, and occluded
with a stainless steel plug. Postsurgical animals exhibiting two
consecutive 4-day estrous cycles were used in experiments. Infusion
experiments were conducted between 8–14 days after surgery. On the day
of an experiment, catheters were flushed with heparinized saline (50
IU) and connected to a syringe pump (Harvard Apparatus, Millis, MA).
Animals were infused with 5 µg/h rhFS-288 in heparinized saline or
heparinized saline alone at a flow rate of 10 µl/min for 6 or 8
h. Specific infusion periods are described in Results and
illustrated in Fig. 7
.
|
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
.
Preovulatory LH and FSH surges of characteristic amplitude and duration
were observed on proestrous evening. The predicted secondary FSH surge,
a broad second rise in FSH that continued through the day of estrus,
was also observed.
|
). Levels decreased by 49% over the
ensuing 12 h to a low of 73 ng/ml at 1800 h
(P < 0.05). Follistatin content then rebounded,
reaching a peak of 184 ng/ml at midnight on proestrus
(P < 0.05 vs. 1800 h) before declining
throughout the day of estrus (P < 0.05). The pituitary
follistatin content was reflected in serum, where a similar, but
statistically nonsignificant, pattern of follistatin was evident.
|
, note arrow),
before the 49% fall in follistatin content. Follistatin mRNA increased
2.5-fold between Pro 1800–2100, preceding the 2.5-fold rebound in
follistatin content. Follistatin mRNA levels thereafter decreased
coincident with the decline in follistatin content. The peak at Pro
2100 and subsequent decline in follistatin mRNA are similar to but
delayed relative to our previous measurements (17). This probably
reflects a difference in the circadian rhythm of the animal colonies
used in the two studies, as evidenced by a similar delay in the LH
surge (Fig. 1
).
|
). After the trough in
follistatin content, FSHß mRNA exhibited a 2.6-fold surge, which
peaked at Pro 2400.
Pituitary follistatin content and unbound serum activin are
inversely related
The measured changes in pituitary follistatin content would be
predicted to alter the amount of pituitary activin not bound to
follistatin, which probably represents the biologically active
fraction. This possibility was explored using an ELISA specific for
unbound activin A. We were unable to measure activin in crude pituitary
extracts due to nonspecific interference; however, unbound activin A
could be measured in the serum. Levels of activin A were not detectable
(<70 pg/ml) at Pro 1200, the first time point examined (Fig. 4). A large peak in activin A was observed at Pro 1800
(1215 pg/ml), coincident with the trough in pituitary follistatin
content. Activin A decreased during the rebound in follistatin at Pro
2400, then exhibited a second peak (634 pg/ml) at 0300 h on estrus
(Est 0300) as follistatin content declined on estrus morning.
|
, left panel),
although basal expression of FSHß mRNA increased on proestrus
compared to that on other days of the cycle (Fig. 5, inset).
Additional experiments compared dispersed pituitary cells harvested
from animals at Pro 2000, during the primary gonadotropin surge, to
cells harvested from animals at 2000 h on metestrus (Fig. 5, right panel). These experiments confirmed the difference in
basal expression observed at 1000 h, but again failed to detect
any difference in response to activin.
|
) and serum FSH (36% decrease; Fig. 6A), with no
change in serum LH. Serum follistatin was also measured to determine
whether carotid infusions altered serum concentrations. Follistatin
levels observed after infusion varied greatly. Two of four animals
exhibited serum levels that were not different from those in
saline-infused controls, and the other two follistatin-infused animals
exhibited elevated serum levels (Fig. 6C). Nonetheless, all animals
receiving follistatin exhibited a similar degree of FSH suppression
relative to saline-infused animals, suggesting that an effective, but
variable, amount of follistatin reached the pituitaries.
|
illustrates the infusion
periods (gray bars) relative to serum FSH and pituitary
FSHß mRNA levels (data from Figs. 1 and 3). One infusion period
(1O; Pro 1500–2100) encompassed the primary serum FSH
surge as well as the onset of the proestrus peak in FSHß mRNA levels.
A second infusion period (2O; Pro 2100 to Est 0300) spanned
the peak in FSHß mRNA and terminated at the peak of the secondary
serum FSH surge. A third group of animals (Di) was infused on diestrus
(1000–1800 h) for comparison.
When follistatin was infused from Pro 1500–2100 (1O),
levels of FSHß mRNA were decreased by 24% compared to those in
saline-infused animals (Fig. 7B, top panel). Although this
difference did not reach statistical significance, an equivalent (26%)
and statistically significant decrease in the primary serum FSH surge
was observed (Fig. 7B, bottom panel). More substantial
changes were observed when follistatin was infused from Pro 2200-Est
0400 (2O). In these experiments, the peak in FSHß mRNA
was reduced by 63%, and the secondary serum FSH surge was reduced by
47%. Infusion of follistatin on diestrus was without significant
effect on FSHß mRNA or FSH secretion. In all cases, serum estradiol
levels were not significantly different between treatment groups, and
there was no significant correlation between serum estradiol and FSH
(data not shown).
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
An important observation was the presence of reciprocal changes in
pituitary follistatin content and free activin A in serum. The
follistatin content fell and serum free activin levels rose during the
afternoon of proestrus, immediately preceding a sharp rise in levels of
FSHß mRNA. The ensuing peak in FSHß mRNA, in turn, preceded the
secondary serum FSH surge, suggesting that new FSH synthesis may be
necessary for the generation of this surge. Arterial infusion of
follistatin to neutralize endogenous activin suppressed both the peak
in FSHß mRNA and the secondary serum FSH surge, demonstrating that
activin is required for the increase in FSHß mRNA. Based on these
data, we propose a model in which the decrease in pituitary follistatin
on proestrus initiates a series of events that is permissive for, but
does not necessarily cause, the secondary FSH surge (Fig. 8).
|
The secondary surge of FSH in serum appears to occur in response to several related events. Previous measurements of pituitary FSH content during the estrous cycle demonstrate that FSH stores are depleted by the primary FSH surge (27). FSH content does not recover before the secondary FSH surge, consistent with the hypothesis that the proestrus increase in FSHß mRNA is required for the synthesis of new FSH that is released as the secondary FSH surge. The 13-fold increase in FSHß mRNA (Pro 0900 to Pro 2400) seems sufficient to support the observed 4-fold rise in serum FSH (Pro 0900 to Est 0300). Although it is possible that this newly synthesized FSH is released constitutively, a second decrease in pituitary follistatin and increase in serum activin A occur simultaneously with the secondary serum FSH surge. Follistatin infusion also blocks the secondary serum FSH surge by nearly 50%, consistent with a role for activin. However, FSHß mRNA levels are also blocked by over 60%, and follistatin suppression of serum FSH might thus reflect a decrease in FSH synthesis rather than a direct effect on FSH release.
Also contributing substantially to the secondary serum FSH surge is the coincident decrease in circulating inhibin (28, 29, 30, 31). Inhibin otherwise exerts a negative influence on pituitary FSH release, although the cellular mechanisms by which inhibin suppresses FSH are not known. Of interest, it has been demonstrated that inhibin blocks activin stimulation of FSHß mRNA levels in vitro (26). If inhibin has similar activity in vivo, it is possible that activin blockade is a common mechanism for the actions of inhibin and follistatin. If so, this convergence would provide an efficient means of integrating gonadal and pituitary input to the control of FSH synthesis and release. This mode of inhibin action is equally plausible whether inhibin blocks activin signaling through its ability to compete for binding to the activin receptor (32) or through an intracellular pathway linked to the as yet unidentified inhibin receptor.
Several aspects of this model remain to be investigated, and a number of interesting questions remain. One unexpected finding was that serum activin A reflected the cyclic pattern of pituitary follistatin content. Previous immunocytochemistry had detected exclusively activin ßB-subunit in the pituitary (33), and neutralization experiments demonstrated the presence of activin B in pituitary cell culture medium (15). In the current experiments, we were unable to measure activin A in pituitary extracts due to technical limitations of the assay, and we did not attempt to measure activin B. However, we detected both activin ßA- and ßB-subunit mRNAs in the pituitary by reverse transcription-PCR (17), and serum activin A increased dramatically after ovariectomy (data not shown), suggesting that serum activin levels reflect at least in part events in the pituitary. It is still possible that serum activin A is derived from a tissue, other than the pituitary, that is sensitive to the loss of gonadal feedback. Even if this is the case, however, the appearance of free activin in the serum during periods of decreased pituitary follistatin suggests that activin within the pituitary is similarly unbound and thereby biologically active at the gonadotrope during periods of decreased pituitary follistatin content. It also appears likely that the pituitary synthesizes both activin A and B.
It is difficult to estimate the efficiency with which the follistatin infusions used in the current experiments neutralize endogenous activin. Higher follistatin concentrations (10 µg/h) and longer infusions (12 h) were not more effective (data not shown), although the current protocol blocked FSHß mRNA and FSH secretion by only 25% and 35% in OVX animals. The infusions were more effective in normally cycling animals, but it remains likely that infused follistatin neutralizes less than 100% of pituitary activin. Based on this reasoning, the contributions of activin to the primary and secondary FSH surges deduced from the current experiments are probably underestimates.
If the proposed model is correct, perhaps the most intriguing unanswered question is what causes pituitary follistatin to decrease on proestrus morning. It is probable that the decrease in follistatin mRNA combined with ongoing secretion of follistatin are sufficient to cause the decrease in follistatin cell content. The signal for decreasing follistatin mRNA, however, is not yet known. The decrease in follistatin mRNA precedes the GnRH surge. Although GnRH pulse frequency may increase before the surge (34), higher frequency and continuous GnRH stimulate, rather than suppress, follistatin mRNA in vitro (16, 35). Thus, GnRH is a better candidate signal for the rebound in follistatin mRNA on proestrous evening than the decrease on proestrous morning. Two other potential mediators of follistatin gene expression are the gonadal steroids, estradiol and progesterone. Estradiol peaks and progesterone exhibits a nadir on proestrus morning. If estradiol suppresses or progesterone stimulates follistatin gene expression, one or both of these steroids might account for the decrease in follistatin mRNA.
In conclusion, we find that pituitary follistatin content and free activin are inversely related during the estrous cycle in rats. Free activin peaks during and appears to be responsible for a large portion of the secondary FSH surge, with a potentially smaller contribution to the primary FSH surge. We suggest that changes in pituitary follistatin are early events in the complex cascade that culminates in the secondary FSH surge and consequent follicular recruitment.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
2 Current address: Endocrine Pharmacology Group, Department 46R-AP10,
Abbott Laboratories, 100 Abbott Park Road, Abbott Park, Illinois
60064.
Received December 18, 1996.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
 |
|
 |
|
  J. P. Moore ,Jr. and S. J. Winters Weaning and the Developmental Changes in Follicle-Stimulating Hormone, Pituitary Adenylate Cyclase-Activating Polypeptide, and Inhibin B in the Male Rat Biol Reprod, April 1, 2008; 78(4): 752 - 760. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. L. Blount, J. M. Vaughan, W. W. Vale, and L. M. Bilezikjian A Smad-binding Element in Intron 1 Participates in Activin-dependent Regulation of the Follistatin Gene J. Biol. Chem., March 14, 2008; 283(11): 7016 - 7026. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 V. G. Thackray and P. L. Mellon Synergistic Induction of Follicle-Stimulating Hormone {beta}-Subunit Gene Expression by Gonadal Steroid Hormone Receptors and Smad Proteins Endocrinology, March 1, 2008; 149(3): 1091 - 1102. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Su, F. Shafiee-Kermani, A. J. Gore, J. Jia, J. C. Wu, and W. L. Miller Expression and Regulation of the {beta}-Subunit of Ovine Follicle-Stimulating Hormone Relies Heavily on a Promoter Sequence Likely to Bind Smad-Associated Proteins Endocrinology, September 1, 2007; 148(9): 4500 - 4508. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. B Lee, V. Khivansara, M. M Santos, P. Lamba, T. Yuen, S. C Sealfon, and D. J Bernard Bone morphogenetic protein 2 and activin A synergistically stimulate follicle-stimulating hormone {beta} subunit transcription J. Mol. Endocrinol., February 1, 2007; 38(2): 315 - 330. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M. McGillivray, V. G. Thackray, D. Coss, and P. L. Mellon Activin and Glucocorticoids Synergistically Activate Follicle-Stimulating Hormone {beta}-Subunit Gene Expression in the Immortalized L{beta}T2 Gonadotrope Cell Line Endocrinology, February 1, 2007; 148(2): 762 - 773. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. M Bilezikjian, A. L Blount, C. J Donaldson, and W. W Vale Pituitary actions of ligands of the TGF-{beta} family: activins and inhibins. Reproduction, August 1, 2006; 132(2): 207 - 215. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Sidis, A. Mukherjee, H. Keutmann, A. Delbaere, M. Sadatsuki, and A. Schneyer Biological Activity of Follistatin Isoforms and Follistatin-Like-3 Is Dependent on Differential Cell Surface Binding and Specificity for Activin, Myostatin, and Bone Morphogenetic Proteins Endocrinology, July 1, 2006; 147(7): 3586 - 3597. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Lamba, M. M Santos, D. P Philips, and D. J Bernard Acute regulation of murine follicle-stimulating hormone {beta} subunit transcription by activin A J. Mol. Endocrinol., February 1, 2006; 36(1): 201 - 220. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T M Lovell, P G Knight, and R T Gladwell Variation in pituitary expression of mRNAs encoding the putative inhibin co-receptor (betaglycan) and type-I and type-II activin receptors during the chicken ovulatory cycle J. Endocrinol., September 1, 2005; 186(3): 447 - 455. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. D. Cherrington, T. A. Farmerie, C. A. Lents, J. D. Cantlon, M. S. Roberson, and C. M. Clay Activin Responsiveness of the Murine Gonadotropin-Releasing Hormone Receptor Gene Is Mediated by a Composite Enhancer Containing Spatially Distinct Regulatory Elements Mol. Endocrinol., April 1, 2005; 19(4): 898 - 912. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. A. Prendergast, L. L. Burger, K. W. Aylor, D. J. Haisenleder, A. C. Dalkin, and J. C. Marshall Pituitary Follistatin Gene Expression in Female Rats: Evidence That Inhibin Regulates Transcription Biol Reprod, February 1, 2004; 70(2): 364 - 370. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. C. Chapman and T. K. Woodruff Betaglycan Localization in the Female Rat Pituitary: Implications for the Regulation of Follicle-Stimulating Hormone by Inhibin Endocrinology, December 1, 2003; 144(12): 5640 - 5649. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Schneyer, A. Schoen, A. Quigg, and Y. Sidis Differential Binding and Neutralization of Activins A and B by Follistatin and Follistatin Like-3 (FSTL-3/FSRP/FLRG) Endocrinology, May 1, 2003; 144(5): 1671 - 1674. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Welt, Y. Sidis, H. Keutmann, and A. Schneyer Activins, Inhibins, and Follistatins: From Endocrinology to Signaling. A Paradigm for the New Millennium Experimental Biology and Medicine, October 1, 2002; 227(9): 724 - 752. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Padmanabhan, D. Battaglia, M. B. Brown, F. J. Karsch, J. S. Lee, W. Pan, D. J. Phillips, and J. Van Cleeff Neuroendocrine Control of Follicle-Stimulating Hormone (FSH) Secretion: II. Is Follistatin-Induced Suppression of FSH Secretion Mediated via Changes in Activin Availability and Does It Involve Changes in Gonadotropin-Releasing Hormone Secretion? Biol Reprod, May 1, 2002; 66(5): 1395 - 1402. [Abstract] [Full Text]
|
|
|
|
|
|
M. Baratta, L.A. West, A.M. Turzillo, and T.M. Nett Activin Modulates Differential Effects of Estradiol on Synthesis and Secretion of Follicle-Stimulating Hormone in Ovine Pituitary Cells Biol Reprod, February 1, 2001; 64(2): 714 - 719. [Abstract] [Full Text]
|
|
|
|
|
|
A. C. Dalkin, D. J. Haisenleder, J. T. Gilrain, K. Aylor, M. Yasin, and J. C. Marshall Gonadotropin-Releasing Hormone Regulation of Gonadotropin Subunit Gene Expression in Female Rats: Actions on Follicle-Stimulating Hormone {beta} Messenger Ribonucleic Acid (mRNA) Involve Differential Expression of Pituitary Activin ({beta}-B) and Follistatin mRNAs Endocrinology, February 1, 1999; 140(2): 903 - 908. [Abstract] [Full Text]
|
|
|
|
|
|
E. Y. Wang, L. B. Draper, E. Lee, A. Polak, P. Sluss, J. Weiss, and T. K. Woodruff Identification of Naturally Occurring Follistatin Complexes in Human Biological Fluids Biol Reprod, January 1, 1999; 60(1): 8 - 13. [Abstract] [Full Text]
|
|
|
|
|
|
A. C. Dalkin, D. J. Haisenleder, J. T. Gilrain, K. Aylor, M. Yasin, and J. C. Marshall Regulation of Pituitary Follistatin and Inhibin/Activin Subunit Messenger Ribonucleic Acids (mRNAs) in Male and Female Rats: Evidence for Inhibin Regulation of Follistatin mRNA in Females Endocrinology, June 1, 1998; 139(6): 2818 - 2823. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Q. Guo, T. R. Kumar, T. Woodruff, L. A. Hadsell, F. J. DeMayo, and M. M. Matzuk Overexpression of Mouse Follistatin Causes Reproductive Defects in Transgenic Mice Mol. Endocrinol., January 1, 1998; 12(1): 96 - 106. [Abstract] [Full Text]
|
|
| ||||||||||
