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Poult Sci 2009. 88:380-386. doi:10.3382/ps.2007-00402
© 2009 Poultry Science Association
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PHYSIOLOGY, ENDOCRINOLOGY, AND REPRODUCTION

Signaling pathways involved in the effect of follicle-stimulating hormone on chick embryo testis cell proliferation1

I. Peralta*, M. C. Romano{dagger} and P. N. Velázquez*,2

* Departamento de Biología Celular y Tisular, Facultad de Medicina, Universidad Nacional Autónoma de México, México Distrito Federal. 04510, México; and {dagger} Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de estudios avanzados (CINVESTAV) IPN, Apdo. Postal 14-740, 07340, México Distrito Federal

2 Corresponding author: pedronv{at}correo.unam.mx


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The aim of the present study was to evaluate the signaling pathways involved in the follicle-stimulating hormone (FSH) regulated mitogenic activity. For this purpose, 18-d-old chick embryo testis cells were dissociated and cultured for 60 h on polycarbonate membranes. The culture medium was Dulbecco modified Eagle’s medium with or without high pure human FSH (hFSH), human recombinant FSH, or different regulators of tyrosine kinase activity as herbimycin A and genistein, or serine/threonine kinases [cyclic adenosine monophosphate (cAMP)-dependent protein serine kinase and protein kinase C] as cAMP, phorbol myristate, and forskolin. In some experiments the regulators were added simultaneously with hFSH. The [3H]-thymidine incorporation was used as an indicator of DNA synthesis. In addition, fragments of chick embryo testis were cultured in the presence or absence of FSH or herbimycin A, and 5-bromo-2'-deoxy-uridine was added to identify the proliferating cell subpopulations. The effect of hFSH on [3H]-thymidine incorporation began at 24 h, and the increment was significant at 36 and 60 h of culture. The hFSH as well as human recombinant FSH significantly stimulated [3H]-thymidine incorporation to testicular cells. The 5-bromo-2'-deoxy-uridine technique showed a high signal in pericordonal and interstitial cells of the hFSH-treated groups, confirming the results obtained using [3H]-thymidine uptake. The treatment with the tyrosine kinase inhibitor herbimycin A increased the [3H]-thymidine uptake, but genistein did not. Regulators of PKA such as cAMP and forskolin, as well as PKC regulators and the phorbol ester phorbol myristate, did not influence cell proliferation. In summary, an inhibitor of tyrosine kinase, herbimycin A, induced per se an increment in chick embryo testis cell proliferation, a fact that strongly suggests that tyrosine kinase signaling pathway functions by inhibiting the proliferation of these cells. On the other hand, the cAMP-PKA pathway had no significant role during the embryonic stage of chick embryo testis. Our results also showed that the effect of FSH on chick embryo cell proliferation occurs mainly in pericordonal and interstitial testis cells.

Key Words: chick embryo • testis • follicle-stimulating hormone • cell proliferation • cell signaling


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Follicle-stimulating hormone (FSH) plays a crucial role in maturation of the ovarian follicle in fowl and in the growth of seminiferous tubules in bird testis (Bahr and Johnson, 1984; Johnson, 2003). This hormone is involved in the differentiation of the granulosa cells of the ovarian follicle and Sertoli cells of the seminiferous tubule in the testis (Griswold, 1993). Follicle-stimulating hormone is also involved in the control of cell proliferation and steroid hormone synthesis in mammalian adult life (Robker and Richards, 1998). Several studies had demonstrated that FSH is important in the regulation of cell proliferation and steroidogenesis in the chick embryo (Velázquez et al., 1997; Pedernera et al., 1999; Mi et al., 2004; Peralta et al., 2004).

Follicle-stimulating hormone initiates its effect by binding to a 75 kDa FSH receptor in the cell membrane receptor. It has been shown that FSH participates in adult gonadal physiology through the activation of different signal pathways, mainly those that involve cyclic adenosine monophosphate (cAMP; Gonzalez-Robayna et al., 2000). The process also involves the activation of G proteins and the cAMP-dependent protein kinase (PKA). The PKA is not the only signaling pathway used by FSH; recent studies had shown that FSH binding to its receptor activates at least 5 signaling pathways in mammalian Sertoli cells (Walker and Cheng, 2005). In fact, phospholipase A, calcium calmodulin, phosphatidylinositol 3-kinase, and MAP kinase signaling pathways have been related to cell proliferation and differentiation as well as with metabolic processes in mammalian granulosa and Sertoli cells (Gonzalez-Robayna et al., 2000; Richards, 2001; Scobey et al., 2001; Walker and Cheng, 2005). Follicle-stimulating hormone also has an important role in the chick embryo gonads cell proliferation (Velázquez et al., 1997; Pedernera et al., 1999) and stimulates the production of cAMP and PKA in mammalian granulosa cells (Richards, 2001). However, the participation of signal pathways different from that of cAMP-PKA had not been investigated in the avian embryo gonadal development.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Materials

Dulbecco modified Eagle’s medium (DMEM), trypsin and soybean trypsin inhibitor were obtained from Gibco BRL (Gaithersburg, MD). Bovine serum albumin and sodium dodecyl sulfate, different regulators of the activity of tyrosine or serine/threonine kinases (herbimycin A, genistein, forskolin, phorbol myristate (PMA), and cAMP were purchased from Sigma Chemical Co. (St. Louis, MO). Human FSH (Fertinorm) and recombinant FSH (Gonal-F) were obtained from Serono (México Distrito Federal); 1 mIU of hFSH is equivalent to 14 ng of hFSH and also contains 0.2 pg of hLH (both immunodetected, Ulloa-Aguirre et al., 1995). Tissue plastic dishes and polycarbonate membranes, 1.0-µm pore size and 13 mm in diameter (Nucleopore), were purchased from Costar (Cambridge, MA). Thymidine [methyl-3H] (2.0 Ci/mmol) and Aquasol were from NEN Dupont (Boston, MA). The 5-bromo-2-deoxy-uridine (BrdU) labeling and detection kit was purchased from Roche (Mannheim, Germany).

Testis Cell Preparation

Testes from 18-d-old chick embryo (Babcock B300) were dissected under sterile conditions, pooled (20 to 30 gonads), and incubated in 0.25% trypsin, in PBS (Ca 2+ and Mg 2+ free) solution for 20 min at 37°C. After trypsin treatment, the dispersed testis cells were treated with 0.5% soybean trypsin inhibitor in DMEM with 1.0 mg/mL of BSA and then washed with 2 changes of DMEM-BSA. The final cell number was counted with the aid of a hematocytometer. Cell viability was always over 90% as established by the trypan blue exclusion test (Tennant, 1964).

Thymidine Incorporation

Samples (5 x 105 cells) of dissociated testis cells were cultured on polycarbonate membranes. The cells were resuspended in 1 to 3 mL of culture medium and aliquots (20 µL) were applied as a small drop in the center of the membrane that was floating on 2 mL of DMEM-BSA plus 0.1 NCi of [3H]-thymidine. When necessary, hFSH (0.5 IU/mL), or rhFSH (0.5 IU/mL), tyrosine kinase regulators (900 nM herbimycin A, 20 µM genistein), or serine/threonine kinases regulators (1 mM cAMP, 0.2 µM forskolin, or 2 µM PMA), or combinations of the kinase regulators with 0.5 IU/mL of hFSH, were added to the medium at the beginning of the culture without any subsequent change of medium or replenishment. Cells were incubated at 37°C in a humidified environment of 95% air and 5% CO2 for 60 h. At the end of the culture, polycarbonate membranes with the cellular aggregates were processed for [3H]-thymidine measurement. Briefly, the cellular aggregate was fixed with methanol-acetic acid (3:1 vol/vol), washed twice with 10% (wt/vol) trichloroacetic acid for 60 min at 4°C, then treated with 2% (wt/vol) SDS for 30 min at 60°C, transferred to scintillation vials, combined with Aquasol (NEN Du Pont), and counted in a Beckman LS 6500 scintillation counter.

In some experiments, tissue fragments were cultured in the presence of BrdU (5-bromo-2'-deoxy-uridine labeling detection kit), and hFSH or herbimycin A were added to the media and the fragments cultured for 60 h. After that period the fragments were processed with the BrdU labeling and detection kit for the morphological study. Sections were observed in a fluorescent microscope. Data were evaluated by ANOVA followed by Duncan’s test for multiple contrast or by Student’s t-test.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The procedure used for culturing the testis cells resulted in a multilayered aggregate. Figure 1Go shows the effect of different doses of hFSH on the [3H]-thymidine incorporation to the testis cells after 60 h in culture. The maximum effect of the hormone was observed with a dose of 2 IU/mL, whereas the hFSH 50% maximal dose (ED50) was 0.25 IU/mL. Figure 2Go shows the influence of time on the [3H]-thymidine incorporation by testis cells. The presence of 0.5 IU/mL hFSH in the culture media caused an increment in [3H]-thymidine incorporation that was significant from 36 h onward.


Figure 1
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  		Figure 1. Dose response curve to high pure human FSH (hFSH) measured as [3H]-thymidine incorporation to the testis cell aggregates cultured for 60 h. Each point represents the mean ± SEM of 3 separate experiments, each with 4 replicates.

 

Figure 2
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  		Figure 2. Time course of the incorporation of [3H]-thymidine to testis cells collected at several times of culture. Bars represent the mean ± SEM of 3 separate experiments each with 4 replicates. Asterisks indicate statistical significance (P < 0.05). White bars = control groups; gray bars = high pure human follicle-stimulating hormone (hFSH) groups.

 
The BrdU technique showed that at 18 d of embryonic life there was an intense cell proliferation (Figure 3Go). The superimposition of the fluorescent images (Figure 3AGo) with the toluidine blue ones (Figure 3BGo) detected the cell subpopulation (Figure 3CGo). The fluorescence signal was observed in the nucleus of the cells and predominated in the interstitium of the testis, corresponding to Leydig cells, and in the pericordonal area (Figure 3Go). The addition of hFSH to the cultures increased the fluorescent signals in the testis interstitium as shown in Figure 3Go (hFSH, A to C). Figure 4Go compared the effect of hFSH and herbimycin with the control group in testis sections treated with BrdU.


Figure 3
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  		Figure 3. Micrographies of semithin slices of chick testis organotypic cultures incubated with 5-bromo-2'-deoxy-uridine in control conditions (control, top panel) or treated with high pure human follicle-stimulating hormone (hFSH, in the bottom panel) from 18-d-old embryos. A) Fluorescent micrography. B) The image had been photographed with light field technique, and was previously stained with hematoxylin-eosin. C) Superimposition of A and B. The subpopulations zones were limited in white. The hFSH cell cultures showed an increased number of fluorescent nucleus.

 

Figure 4
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  		Figure 4. Micrographies of semithin slices of chick testis organotipic cultures incubated with 5-bromo-2-deoxy-uridine from 18-d-old embryos. (A) Control cultures, (B) high pure human follicle-stimulating hormone (hFSH), (C) herbimycin A treatment. The fluorescent signal was more intense in the groups treated with hFSH or herbimycin A.

 
Results showed the enhancement of fluorescence in hFSH and herbimycin-treated cells (Figure 4Go). The effect of hFSH, rhFSH, and tyrosine kinase (PTK) inhibitors genistein and herbimycin A on testis cell proliferation is shown in Figure 5Go. The presence of both types of FSH in the culture media significantly increased cell proliferation estimated by [3H]-thymidine incorporation. The addition of herbimycin A significantly increased cell proliferation, whereas no significant effect was observed with genistein. The effect of herbimycin was similar to that produced by hFSH or rhFSH. The addition of PKA or protein kinase C (PKC) regulators did not modify significantly the testis cell proliferation (Figure 5Go).


Figure 5
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  		Figure 5. Response to high pure human follicle-stimulating hormone (hFSH), human recombinant FSH (rhFSH), and different regulators of the activity of tyrosine or serine/threonine kinases measured as [3H]-thymidine incorporation to chick embryo testis cells cultured for 60 h. Each bar represents the mean ± SEM obtained from 10 separate experiments, each with 4 replicates. *Asterisks indicate statistical significance compared with the control group (P < 0.001). cAMP = cyclic adenosine monophosphate; PMA = phorbol myristate.

 
Figure 6Go shows the effect of hFSH and the different kinase regulators added separately or combined with hFSH. Results shows that again hFSH significantly increased [3H]-thymidine incorporation to testis cells as compared with control cells. The combined addition of hFSH plus genistein, forskolin, or PMA also increased cell proliferation; however, the effect was not statistically different from that of only hFSH (Figure 6Go). The addition of herbimycin A significantly increased [3H]-thymidine incorporation, the result being similar to that of only hFSH; the combination of the gonadotropin plus herbimycin A induced even greater increments (P < 0.05) than those for the PTK regulator alone or the control ones. On the contrary, although the only addition of cAMP did not modify cell proliferation as compared with the control group, the combination of cAMP plus hFSH significantly decreased the proliferative effect of only hFSH.


Figure 6
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  		Figure 6. [3H]-thymidine incorporation to cells cultured for 60 h in the presence of high pure human follicle-stimulating hormone (hFSH), protein kinase modulators, or both. Each bar represents the mean ± SEM obtained from 10 separate experiments, each with 4 replicates. *Asterisks indicate statistical significance compared with the control group (P < 0.001). cAMP = cyclic adenosine monophosphate; PMA = phorbol myristate.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Present results confirm that FSH stimulates chick embryo testis cell proliferation in a dose- and time-response manner (Figures 1Go and 2Go). The BrdU incorporation showed for the first time that proliferation of testis cells occurred in the interstitial and pericordonal cells, which indicates that these populations were actively proliferating at this stage of development (Figure 3Go and 4Go). In accordance with this fact, Woods et al. (1975) had reported the presence of testosterone in the developing chick embryo plasma and also had demonstrated that after a period of gonadal autonomy, the testis comes under the influence of the adenohypophysis (Woods et al., 1981). Furthermore, a peak of high synthetic activity occurs around hatching in the chicken (Romano et al., 1981) and in the perinatal period of mammals. Sertoli cells and spermatogonia were not proliferating so actively; in accordance, it is well known that Sertoli cells proliferate after birth in mammals (Gonzalez-Robayna et al., 2000).

It had been established that cAMP and PKA participates in the signal cascade induced by gonadotropins in mammalian cells; one important role for this signaling pathway is apoptosis prevention (Chun et al., 1996; Johnson, 2003). Similarly, cell survival in granulosa cells from prehierarchal hen follicles is promoted by 8-bro-mo-cAMP (Johnson et al., 1996) Present results add new information on the role of signal cascades on chick embryo testis cells and show that a few of them participate on FSH mechanism of action in the last stage of development. The results strongly suggest that basal cell proliferation of the testis at this particular stage of development is not changed by the addition of cAMP or forskolin to the culture media (Figure 5Go), meaning that cAMP-PKA pathway would not be involved in this process. Because forskolin did not prevent FSH effects on cell proliferation and cAMP did not mimic the FSH effect, it is possible to suggest that cAMP-PKA pathway is not involved in FSH-induced cell proliferation. In light of the Crepieux et al. (2001) findings, these results could suggest that the age of the organism is a factor involved in the testis signaling cascades. On the other hand, PMA, a well-established PKC activator, has been shown to be involved in the signal cascades for mammal granulosa cells events (Peluso et al., 1993). However, PMA did not significantly affect the [3H]-thymidine incorporation to the testis cells, suggesting that PKC is not involved in the FSH-induced cell proliferation of the 18 d-old chick embryo testis.

To investigate the participation of PTK signal cascades in the embryonic life, 2 different inhibitors of PTK were assayed in our model. Because in the present study herbimycin A, a PTK blocker, significantly stimulated cell proliferation, it is possible that these kinases down-regulate cell proliferation in chick embryo testis cells. To this regard it has been shown that proto-oncogene tyrosine-protein kinase Src is part of the tyrosine kinase family and a target for herbimycin A; Src is involved in several cell functions like proliferation, migration, and cell adhesion (Thomas and Brugge, 1997). Herbimycin effects were not significantly increased by the addition of FSH, which suggest they act by the same mechanism of action (Figure 6Go). Interestingly, Src seems to be regulated by the P subunit of protein G, which is coupled to FSH, LH, and other glycoproteins (Ma et al., 2000). The function of Src is not well understood, but it was shown that it activates the ERK kinase, which is regulated by the FSH-PKA signaling pathway in Sertoli cells (Crepieux et al., 2001). The ERK kinase stimulates cyclin D1 and factor E2F, important elements for cell division in adult Sertoli cells (Walker and Cheng, 2005). Therefore, the results of this paper indicate that PTK are involved in the regulation of cell proliferation in the chick embryo testis.

In summary, the present results show that hFSH is a powerful stimulator of testicular cells, particularly interstitial cells as shown by BrdU technique, during the last period of embryonic development. The study also suggests that the cAMP-PKA signaling cascade is not primarily involved in the mechanisms that regulate cell proliferation. The same situation was found for PMA, a PKC regulator. This investigation also indicates that certain kinases like PTK act by inhibiting cell proliferation in the developmental chick testis. Altogether the present results strongly suggest that testis cell proliferation in the chick embryo is modulated by multiple factors that include signals different from the cAMP-PKA signaling cascade.


   ACKNOWLEDGMENTS
 
The study was financed in part by Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT; IN 213306). The authors acknowledge the advice of the biologists Tonatiuh Velázquez Cervantes and Ricardo A. Valdez in the figure design.


   FOOTNOTES
 
1 The study was financed in part by Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT; IN 213306). Back

Received for publication September 28, 2007. Accepted for publication September 22, 2008.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Bahr, J. M., and A. L. Johnson. 1984. Regulation of the follicular hierarchy and ovulation. J. Exp. Zool. 232:495–500.[CrossRef][Web of Science][Medline]

Chun, S. Y., K. M. Eisenhauer, S. Minami, H. Billig, E. Perlas, and A. J. Hsueh. 1996. Hormonal regulation of apoptosis in early antral follicles: Follicle stimulating hormones as a major survival factor. Endocrinology 137:1447–1456.[Abstract]

Crepieux, P., S. Marion, N. Martinat, V. Fafeur, Y. L. Vern, D. Kerboeuf, F. Guillou, and E. Reiter. 2001. The ERK-dependent signalling is stage-specifically modulated by FSH, during primary Sertoli cell maturation. Oncogene 20:4696–4709.[CrossRef][Web of Science][Medline]

Gonzalez-Robayna, I. J., A. E. Falender, S. Ochsner, G. L. Firestone, and J. S. Richards. 2000. FSH stimulates phosphorylation and activation of protein kinase B (PKB/Akt) and serum and glucocorticoid-induced kinase (Sgk): Evidence for A-kinase independent signaling in granulosa cells. Mol. Endocrinol. 14:1283–1300.[Abstract/Free Full Text]

Griswold, M. D. 1993. Actions of FSH on mammalian Sertoli cells. Pages 493–508 in The Sertoli Cell. L. D. Russell and M. D. Griswold, ed. Cache River Press, Clearwater, FL.

Johnson, A. L. 2003. Intracellular mechanisms regulating survival in ovarian follicles. Anim. Reprod. Sci. 78:185–201.[CrossRef][Web of Science][Medline]

Johnson, A. L., J. T. Bridgham, J. P. Witty, and J. L. Tilly. 1996. Susceptibility of avian granulosa cells to apoptosis is dependent upon stage of follicle development and is related to endogenous levels of bcl-xlong gene expression. Endocrinology 137:2059–2066.[Abstract]

Ma, Y.-C., J. Huang, S. Ali, W. Lowry, and X.-Y. Huang. 2000. Src Tyrosine kinase is a novel direct effector of G proteins. Cell 102:635–646.[CrossRef][Web of Science][Medline]

Mi, Y., C. Zhang, M. Xie, and W. Zeng 2004. Effects of follicle-stimulating hormone and androgen on proliferation of cultured testicular germ cells of embryonic chickens. Gen. Comp. Endocrinol. 138:237–246.[CrossRef][Web of Science][Medline]

Pedernera, E., A. L. Solís, D. I. Peralta, and P. N. Velázquez. 1999. Proliferative and steroidogenic effects of follicle stimulating hormona during chick embryo gonadal development. Gen. Comp. Endocrinol. 116:213–220.[Medline]

Peluso, J. J., A. Pappalardo, and B. A. White. 1993. Control of rat granulosa cell mitosis by phorbol ester-, cyclic AMP-, and estra-diol-17beta-dependent pathways. Biol. Reprod. 49:416–422.[Abstract]

Peralta, I., M. C. Romano, and P. N. Velásquez. 2004. Proliferative and steroidogenic effects of follicle-stimulating hormone on cultured chick embryo testis cells. Poult. Sci. 83:1193–1198.[Abstract/Free Full Text]

Richards, J. 2001. New signaling pathways for hormones and cyclic adenosine 3',5'-monophosphate action in endocrine cells. Mol. Endocrinol. 15:209–218.[Abstract/Free Full Text]

Robker, R. L., and J. S. Richards. 1998. Hormonal control of the cell cycle in ovarian cells: Proliferation versus differentiation. Biol. Reprod. 59:476–482.[Free Full Text]

Romano, M., M. C. Aguilar, M. C. Méndez, and E. Pedernera. 1981. Bursa of Fabricius produces in vitro a factor which inhibits the chorionic gonadotropin response of the newly hatched chick testis. J. Steroid Biochem. 15:429–432.[Medline]

Scobey, M. J., S. Bertera, J. P. Somers, S. C. Watkins, A. J. Zeleznik, and W. H. Walker. 2001. Delivery of a cyclic adenosine 3', 5'-monophosphate Response element binding protein (CREB) to seminiferous tubules results in impaired spermatogenesis. Endocrinology 142:948–954.[Abstract/Free Full Text]

Tennant, J. R. 1964. Evaluation of the trypan blue technic for the determination of cell viability. Transplantation 2:685–694.

Thomas, S. M., and J. S. Brugge. 1997. Cellular functions regulated by SRC family kinases. Annu. Rev. Cell Dev. Biol. 13:513–609.[CrossRef][Web of Science][Medline]

Ulloa-Aguirre, A., E. Zambrano, C. Timossi, E. Olivares, A. Quintanar, M. Aguinaga, L. Díaz-Cueto, and J. P. Méndez. 1995. On the nature of the follicle-stimulating signal delivered to the ovary during exogenously controlled follicular maturation. Arch. Med. Res. 26(Suppl.):S219–S230.

Velázquez, P. N., D. I. Peralta, and E. Pedernera. 1997. Proliferative effect in vitro of follicle-stimulating hormone on the left ovary of the chick embryo. Gen. Comp. Endocrinol. 105:40–49.[Medline]

Walker, W. H., and J. Cheng. 2005. FSH and testosterone signaling in Sertoli cells. Reproduction 130:15–28.[Abstract/Free Full Text]

Woods, J. E., J. A. Menella, and R. C. Thommes. 1981. The hypothalamic-adenohypophyseal-gonadal axis in the developing chick embryo. Gen. Comp. Endocrinol. 45:66–73.[Medline]

Woods, J. E., R. M. Simpson, and P. L. Moore. 1975. Plasma testosterone levels in the chick embryo. Gen. Comp. Endocrinol. 27:543–547.[Medline]





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