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Endocrinology Vol. 138, No. 8 3216-3221
Copyright © 1997 by The Endocrine Society

ARTICLES

PRAP, a Prolactin Receptor Associated Protein: Its Gene Expression and Regulation in the Corpus Luteum1

W. R. Duan, T. G. Parmer, C. T. Albarracin, L. Zhong and G. Gibori2

Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612-7342

Address all correspondence and requests for reprints to: Dr. Geula Gibori Department of Physiology and Biophysics, University of Illinois at Chicago, 835 South Wolcott Avenue, Chicago, Illinois 60612-7342. E-mail: GGibori{at}uic.edu


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
We have recently identified, characterized, and cloned a luteal microsomal 32-kDa phosphoprotein that we named PRAP (for PRL-receptor associated protein), and we have demonstrated that PRAP binds to the intracellular domain of the short but not the long form of the PRL receptor. In this study, we used PRAP cDNA to examine the tissue specificity, the developmental expression, and the hormonal regulation of PRAP gene expression. Northern blot analysis revealed that in the corpus luteum, PRAP cDNA hybridized to multiple transcripts (5.5 kb, 4.3 kb, and 1.8 kb), with the smallest transcript (1.8 kb) corresponding to the size of the cDNA clone. However, none of these transcripts were detected in any other tissues examined. PRAP appears to be tightly regulated by steroids and PRL. When pregnant rats were treated with aminoglutethimide, a steroid synthesis inhibitor, all three PRAP transcripts became barely detectable. Similar results were obtained when all luteotropic support was removed by hypophysectomy and hysterectomy. Estradiol up-regulated PRAP expression and, more specifically, the two lower transcripts. PRL had no stimulatory effect on PRAP messenger RNA (mRNA) expression but caused a substantial increase in the level of PRAP protein when administered to hypophysectomized pregnant rat, suggesting that PRL may stabilize this protein. Similar dissociation between levels of mRNA and protein were observed during luteal development. Although both PRAP mRNA and protein were barely detectable in early pregnancy, their expression increased abruptly from midpregnancy; however, whereas levels of PRAP mRNA declined from day 18, those of the protein remained elevated until parturition.

In summary, results of this study have defined the tissue specificity and developmental expression of PRAP mRNA during pregnancy. The data have also revealed that the gene expression of this protein is up-regulated by estradiol, suggesting a pivotal role for PRAP in the synergistic action of estradiol and PRL on the function of the rat corpus luteum.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
WE HAVE PREVIOUSLY identified and characterized a microsomal phosphoprotein highly expressed in the ovary (1, 2). Whereas this protein is absent in all other steroidogenic and nonsteroidogenic tissues examined in the rat, it is clearly expressed in corpora lutea of different species, including the mouse, hamster, cow, pig, and human (2). Immunocytochemical localization in the ovary of the pregnant rat demonstrated that this protein was selectively and abundantly expressed in the corpus luteum (2). However, even though undetectable by immunocytochemistry, Western blot analysis showed this protein to be present in the follicle at levels markedly lower than in the corpus luteum. Although analysis of theca and granulosa cells revealed the presence of this protein in both cell types (2), its expression in the corpus luteum is highly cell-specific and is exclusively limited to the large luteal cell (1, 2). It is the large luteal cell that expresses the bulk of PRL receptors and responds to both PRL and estradiol with increased progesterone and protein synthesis (3).

We have recently demonstrated that this protein is phosphorylated on tyrosine and associates with the intracellular domain of the short form of the PRL receptor (4). We named it PRAP for PRL receptor-associated protein (4). Our successful cloning of PRAP revealed no significant homology to other known proteins (4), and hydropathy plot revealed an unusual structure of a membrane protein with an extracellular loop. The deduced amino acid sequence indicates several sites of glycosylation in the extracellular domain and the presence of a putative tyrosine phosphorylation site in the intracellular domain, similar to the JAK2 (Janus kinase 2) phosphorylation sites on Stat1 and Stat5, making PRAP a putative target of JAK2.

The cloning of PRAP has prompted us to examine the expression, the tissue specificity, and the developmental regulation of this gene. We have also examined the roles of estradiol and PRL on the regulation of PRAP gene expression.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Materials
Dimethylsulfoxide (DMSO), aminoglutethimide, medium, and other chemicals were obtained from Sigma Chemical Co. (St. Louis, MO). 17ß-estradiol was a product of Steraloids Co. (Wilton, NH). SILASTIC brand medical grade tubing was purchased from Dow Corning Corp. (Midland, MI). Random primed DNA labeling kit was the product of Boehringer Mannheim Biochemicals (Indianapolis, IN). GeneScreen Plus nylon membrane was purchased from New England Nuclear Research Systems (Boston, MA). [{alpha}-32P]dCTP was obtained from Amersham Corp. (Arlington Heights, IL).

Animal models
Pregnant Sprague-Dawley rats were purchased from Sasco Animal Laboratory (Oregon, WI). The day that sperm was found in the vagina is considered day 1 of pregnancy. Rats were housed in a controlled environmental temperature (24–26 C), kept under a 14-h light, 10-h dark cycle, and had free access to animal chow and water.

To study the effect of aminoglutethimide, a P450scc inhibitor, on the expression of PRAP protein and its messenger RNA (mRNA), day 12 pregnant rats were injected with aminoglutethimide (25 mg/day) dissolved in DMSO ip once daily on days 12 and 13 of gestation and were killed on day 14. Control rats received DMSO only.

In experiments that involved estradiol, the well characterized hypophysectomized and hysterectomized pregnant rat model was used (5, 6). Hypophysectomy was performed on rats on day 12 of pregnancy under ether anesthesia by the transauricular approach using a stereotaxic instrument. A successful hypophysectomy was judged by the complete recovery of the pituitary at the time of operation and the absence of any hypophyseal fragments in the fossa at autopsy. Data from rats with incomplete hypophysectomy were discarded. Hysterectomy was performed through a midline abdominal incision. A SILASTIC implant (2 cm) containing 17ß-estradiol was implanted sc in the neck on day 12 of pregnancy immediately after surgery and was maintained until autopsy (day 15).

To examine the effect of PRL on PRAP, rats were hypophysectomized on day 3 of pregnancy and were treated sc with either vehicle or 125 µg PRL twice daily for 3 days (NIDDK ovine PRL-18; 30 IU/mg). This treatment is known to sustain corpus luteum function (7).

Tissue preparation and subcellular fractionation
In each experiment, corpora lutea were dissected from the adhering ovarian follicles and interstitial tissues, weighed and rapidly frozen at -80 C until processed.

Corpora lutea were suspended in 1 ml cold homogenization buffer containing 50 mM Tris-HCl (pH 7.4), 250 mM sucrose, 2 mM EDTA, 1 mM phenylmethyl-sulfonylfluoride, and 1 mM DTT followed by homogenization in a Potter-Elvejhem homogenizer. Homogenates were fractionated by differential centrifugation (1).

Granulosa cell culture
The 27- to 28-day-old immature female Sprague-Dawley rats (Sasco) were treated with 0.15 IU hCG sc twice daily for 2 days and followed by 10 IU hCG the third day via the tail vein. Seven hours later, preovulatory follicles were isolated. The cells were cultured in the DMEM-Ham’s (DMEM/F-12, 1:1) with 15 mM HEPES, 3.15 g/liter glucose, 1% FBS, 100 IU penicillin G, 100 µg/ml streptomycin, and 0.25 µg/ml amphotericin B. Follicles were incubated sequentially in 6 mM EGTA in DMEM/F-12 and 0.5 M sucrose in DMEM/F-12. Individual follicles were popped using 30-gauge needles and pressed gently with the bevel of the needle. Granulosa cells were extruded into the medium and pelleted at 100 x g for 10 min. Cells were counted with hemocytometer using trypan blue to distinguish the viability. Cells were plated in 60-mm Petri dishes (Corning, NY) at about 8 x 105 cells/ml and incubated at 37 C in a humidified atmosphere with 95% air and 5% CO2. After 3 days of incubation, medium was changed and cells were treated with different doses of 17ß-estradiol for 24 h. Cells were harvested and RNA was extracted.

Western blot analysis
After gel electrophoresis, the proteins were transferred onto nitrocellulose filters at 250 mA for 16–20 h at 4 C (8). Immunoblotting was performed by blocking nonspecific binding with 3% BSA in TBS (20 mM Tris base, 500 mM NaCl, pH 7.5) for 1 h followed by three 5-min washes with TBST [TBS plus 0.05% (vol/vol) Tween 20]. The appropriately diluted (1:1000) PRAP antisera, generated as previously described (2), was added to the filters and allowed to incubate overnight at 4 C or at room temperature for 2 h. The blots were then washed in TBST, three times for 5 min each. Immunoreactive proteins were detected using either a secondary antibody (1:5000) labeled with alkaline phosphatase (Stratagene, La Jolla, CA) and/or 125I-labeled protein A (2 x 105cpm/ml, ICN, Irvine, CA).

Northern blot analysis
Total RNA was isolated from corpora lutea and other endocrine and nonendocrine tissues according to the method of Chirgwin (9). RNA was quantified by reading the absorbance at 260/280 nm in a Perkin-Elmer Lambda 4B spectrophotometer (Norwalk, CT). Total RNA (20 µg/lane) was fractionated by electrophoresis on a 1% agarose gel containing 3.7% formaldehyde in 1-fold concentrated 3-morpholinopropanesulfonic acid (MOPS) buffer and blotted to nylon membranes by capillary transfer. RNA was fixed to the membrane by baking in vacuo at 80 C for 2 h. Ethidium bromide staining confirmed that the ribosomal RNAs were intact and that equal amounts of RNA were loaded in each lane.

The PRAP cDNA was isolated as previously described by our laboratory (4). Either a 653 or a 1161 EcoRI-cut fragment was used for hybridization. The cDNA probes were labeled with [{alpha}-32P]dCTP using random primed DNA labeling kit. Blots were prehybridized for 4 h or overnight at 42 C in a solution containing 50% formamide, 6 x SSC, (0.9 M NaCl, 0.09 M Na citrate) 1% SDS, 50 mM sodium phosphate, 1 x Denhardt’s and 100 µg/ml sonicated salmon sperm DNA. Hybridization was completed in the same solution containing 32P-labeled cDNA probe at 42 C for 16 h. Blots were washed once in 2 x SSC and 1% SDS at room temperature for 15 min, twice in 0.2 x SSC and 0.5% SDS for 20 min at 42 C. The final wash was performed in 0.1 x SSC, 0.1% SDS at 60 C for 15–30 min. Radioactivity was monitored after each wash. The blot was then exposed to Kodak XAR-5 film, with or without an intensifying screen (DuPont, Wilmington, DE) overnight or 1–3 days at -80 C.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Pattern of expression and tissue specificity of PRAP mRNA
To examine the pattern of PRAP mRNA expression and its tissue specificity, total RNA was extracted from corpora lutea, and other endocrine (uterus, adrenal, placenta) and nonendocrine (heart, liver, small intestine) tissues obtained from day 15 pregnant rats. Testicular RNA was obtained from adult male rats. Equal amounts of RNA (20 µg) were separated on 1% agarose-formaldehyde gels, transferred to Genescreen membranes, and probed with PRAP cDNA fragment. As shown in Fig. 1Go, Northern blot analysis revealed that in the corpus luteum, PRAP cDNA hybridized to multiple transcripts (5.5 kb, 4.3 kb, and 1.8 kb), with the smallest transcript (1.8 kb) corresponding to the size of the cDNA clone. However, none of these transcripts were detected in any other tissue examined.



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  		Figure 1. Tissue specificity of PRAP mRNA. Total RNA was isolated from endocrine (uterus, adrenal, placenta, decidua, testes, corpus luteum) and nonendocrine (heart, liver, small intestine) tissues obtained from day 15 pregnant rats, or from testes of male rats. Equal amounts of RNA (20 µg) were subjected to electrophoresis, transferred to Genescreen membranes, and hybridized with a {alpha}32P-labeled PRAP cDNA probe. The positions of the 28S and 18S ribosomal bands are indicated. A, antimesometrial; M, mesometrial.

 
Developmental expression of PRAP in the corpus luteum throughout pregnancy
To determine the developmental expression of PRAP in the corpus luteum throughout gestation, corpora lutea were isolated from pregnant rats at different stages of pregnancy. Total RNA and protein were extracted and subjected to Northern and Western blot analyses, respectively, using PRAP cDNA and the antibodies developed in the laboratory (2, 10). Developmental study shown in Fig. 2Go indicates that PRAP mRNA (upper panel) and protein (lower panel) are barely detectable in early pregnancy but became abundantly expressed from midpregnancy. Interestingly, despite a decline in the expression of mRNA at the end of pregnancy, levels of PRAP protein remained elevated suggesting that PRAP has a long half life.



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  		Figure 2. Expression of PRAP protein and mRNA during pregnancy. Upper panel, Corpora lutea from four to five rats were isolated and pooled on each day of pregnancy between days 5 and 21 and processed for RNA. Total RNA (20 µg) was separated on 1% agarose-formaldehyde gels, and Northern blot analysis was conducted using PRAP cDNA. The positions of 28S and 18S are shown. Lower panel, Corpora lutea from three to four rats were isolated on each day of pregnancy between days 3 and 21. Microsomal fractions were obtained by differential centrifugation (1). Microsomal proteins were separated by SDS-PAGE on 7–18% gradient gels and then transferred to nitrocellulose. Western blot analysis was performed using antisera to PRAP. Immunoreactive proteins were detected using 125I-labeled protein A.

 
Hormonal regulation of PRAP expression
To examine whether PRAP mRNA expression is regulated in the corpus luteum by steroids, steroid biosynthesis was blocked with administration of aminoglutethimide (a P450scc inhibitor) to day 12 pregnant rats for 2 days. Corpora lutea were isolated. Luteal proteins and total RNAs (20 µg) were separated on SDS-PAGE and agarose gels, transferred, and hybridized with PRAP antibody and 32P-labeled PRAP cDNA. As shown in Fig. 3Go (right panel), when steroid synthesis in the corpus luteum was blocked by administration of aminoglutethimide, all three PRAP mRNA transcripts almost disappeared from the corpus luteum and a marked decrease in PRAP protein was observed (Fig. 3Go, left panel), suggesting that PRAP mRNA is tightly regulated within the corpus luteum by steroids.



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  		Figure 3. Effect of aminoglutethimide on the expression of PRAP protein and mRNA. Day 12 pregnant rats were injected once daily with aminoglutethimide (AG; 25 mg/day), or DMSO only (control; C) for 2 days. Corpora lutea were isolated. Left panel, Microsomal proteins were obtained by differential centrifugation, separated by SDS-PAGE gradient gel and stained with Coomassie blue. Right panel, Total RNA (20 µg) was separated on 1% agarose-formaldehyde gels and Northern blot analysis was performed using PRAP cDNA probe. The positions of 28S and 18S are shown. The ethidium bromide stain of the 28S is shown below.

 
Because the rat corpus luteum is the site of expression and action of estradiol (3), we examined whether estradiol up-regulates PRAP mRNA expression. In this experiment, we used the day 12 hypophysectomized and hysterectomized pregnant rat model whose corpora lutea are highly responsive to estradiol (3, 11). These rats were treated with or without estradiol (via a 2-cm implant) for 72 h. Day 15 intact pregnant rats served as control. Corpora lutea were isolated, total RNA was extracted, and 20 µg RNA were separated on agarose gels and hybridized with PRAP cDNA as shown in Fig. 4Go. Removal of all tropic hormones by hypophysectomy and hysterectomy caused an almost total disappearance of all PRAP transcripts. Treatment with estradiol enhanced the levels of the middle and lower transcripts but had no stimulatory effect on the largest transcript.



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  		Figure 4. Differential regulation of PRAP mRNA transcripts by estradiol. Pregnant rats were hypophysectomized and hysterectomized on day 12 of pregnancy and treated with (+E) or without (-E) estradiol (2-cm implant) for 3 days. Total RNA was isolated from corpora lutea. Additionally, RNA was also extracted from corpora lutea of day 15 intact pregnant rats (C). RNA was separated on 1% agarose-formaldehyde gels, and Northern blot analysis was performed using PRAP cDNA probe. The positions of 28S and 18S are shown. The ethidium bromide stain of the 18S is shown below.

 
To further examine the effect of estradiol, we used highly luteinized granulosa cells. Cells were treated with estradiol for 24 h, and RNA was isolated and subjected to Northern analysis using PRAP cDNA (Fig. 5Go). Interestingly, whereas estradiol up-regulated PRAP expression in the corpus luteum (Fig. 4Go), it had no stimulatory effect on PRAP mRNA expression in cultured granulosa cells at any dose used (Fig. 5Go).



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  		Figure 5. Expression and effect of estradiol on PRAP mRNA in cultured granulosa cells. Immature granulosa cells were isolated and cultured as described in Materials and Methods. Cells were treated with different doses of 17ß-estradiol (molar) for 24 h and were harvested. RNA was extracted and separated on 1% agarose-formaldehyde gels. Northern blot analysis was performed using PRAP cDNA probe. The blot was exposed to a film with an intensifying screen for 5 days. Ethidium bromide stain of the 18S is shown below.

 
Because PRAP associates with the short form of the PRL receptor, we examined the role of PRL on PRAP expression. Pregnant rats were hypophysectomized on day 3 and were treated with or without PRL for 3 days (7). Day 7 normal pregnant rats were used as control. Corpora lutea were isolated from these rats and subjected to Western and Northern blot analysis. The results shown in Fig. 6Go indicate that PRL does not up-regulate PRAP mRNA expression (right panel) but causes an increase in the levels of PRAP protein (left panel).



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  		Figure 6. Effect of PRL on PRAP expression in the corpus luteum. Pregnant rats were hypophysectomized on day 3 and treated with (+PRL) or without (-PRL) (125 µg/rat, twice daily) for 3 days. Corpora lutea from these treatments as well as from intact day 7 pregnant rats (NP) were isolated. Luteal proteins and total RNA were extracted and subjected to Western and Northern analysis, respectively. Northern analysis (right panel) was performed as described in Material and Methods using PRAP cDNA. The blot was exposed to a film with an intensifying screen for 3 days at -80 C. The ethidium bromide stain of the 18S is shown below. Western analysis (left panel) was performed as described in Material and Methods using PRAP antibody. The immunoreactive proteins were visualized with alkaline phosphatase labeled secondary antibody.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
Results of this investigation have defined the tissue specificity, the developmental expression, and the hormonal regulation of PRAP mRNA in the rat corpus luteum. Northern blot analysis, using the cDNA isolated from a rat corpus luteum cDNA library, showed two large dominant transcripts (5.5 kb and 4.3 kb) and a small transcript (1.8 kb) in the corpus luteum. The DNA clone obtained is about 1.8 kb, which matches the size of the smallest transcript. The different sizes of mRNA species may arise from differential transcriptional initiation, alternative splicing of the coding region, and 3' alternative polyadenylation or may represent mRNAs from distinct genes that may encode different isoforms. In any case, neither one of the three transcripts were detected in other endocrine and nonendocrine tissues of the rat further establishing the specificity of PRAP to the ovary.

The fact that PRAP is not detectable in rat testes, placenta, and adrenals, all highly steroidogenic tissues, suggests that this protein has no apparent role in overall steroidogenesis. However, PRAP appears to be tightly regulated by steroids. When pregnant rats were treated with aminoglutethimide, a steroid synthesis inhibitor, all three PRAP transcripts became barely detectable. Similar results were obtained when all luteotropic support was removed by hypophysectomy and hysterectomy. Estradiol up-regulated PRAP expression, and, more specifically, the two lower transcripts. Interestingly, despite the fact that estradiol does not stimulate the largest transcript of PRAP, it does up-regulate PRAP synthesis (1), suggesting that the largest transcript may not be translated into protein and its regulation may involve different mechanisms.

The ontogeny studies revealed that PRAP becomes highly expressed at midpregnancy, just at a time when PRL secretion by the pituitary ceases and when the placenta becomes secreting large amounts of rat placental lactogens and androgens that are aromatized to estradiol in the corpus luteum (3). PRAP’s abrupt expression is most probably induced by luteal estradiol. At midpregnancy, both luteal P450 aromatase and estradiol receptor levels increase markedly (12), rendering the corpus luteum highly responsive to estradiol. The very high levels of PRL related hormones secreted at this stage by the placenta may also help stabilize this protein. Indeed PRL treatment can increase levels of PRAP protein without affecting those of its mRNA. Whether the up-regulation of PRAP by PRL is the result of enhanced translation and/or prevention of degradation remains to be investigated. One possibility is that PRL may affect the association of PRAP with the PRL receptor in a way that stabilizes this protein and prevents its degradation. Indeed PRAP, which appears to be a membrane-associated protein, binds to the intracellular domain of the short form of the PRL receptor (4).

Two different forms of the PRL receptor have been identified in the rat (13, 14). Both forms are coexpressed in PRL-responsive tissues including the corpus luteum (15). Signaling by the PRL receptor appears to occur as a result of ligand-induced dimerization and activation of molecules that associate with the intracellular domain of the receptor, such as JAK2. JAK2 is a tyrosine kinase that, once activated, phosphorylates associated transcription factor(s) belonging to the Stat (signal transducers and activators of transcription) family. Whereas the long form of the PRL receptor signals through the JAK2/Stat5 system, the short form is unable to promote Stat5 phosphorylation and confer transcriptional induction (16). It is not clear how PRL signal is transduced through the short form of the PRL receptor. Although results from several laboratories indicate that the short form is unlikely to be involved in gene transcription and cell proliferation (17, 18, 19), a recent report indicates that PRL can induce cell proliferation in NIH 3T3 cells through the short form of the PRL receptor (20). The only protein besides JAK2 shown to date to associate with the short form of the PRL receptor is PRAP. In contrast to JAK2, which binds to both receptor types (21), PRAP associates exclusively with the short form (4). Because PRAP has a putative site for JAK2 phosphorylation and is phosphorylated on tyrosine (4), it is highly possible that PRAP may mediate PRL signaling through the short form of the receptor. However, our findings that PRAP becomes highly expressed only from midpregnancy, at a time when large amounts of PRL-related proteins are secreted in the circulation by the placenta, suggest that PRAP may play a role when very high levels of PRL/PRL-related hormones are present. Dimerization of the receptor is essential for PRL signaling, and high levels of hormone can cause binding to individual receptors, thus prevent dimerization and signaling (22). However, despite the very high levels of the placental PRL-like hormone in the circulation from day 11 (23), no loss in responsiveness to PRL-signaling could be detected. It is therefore tempting to suggest that PRAP may, by binding to the short form of the PRL receptor, increase the binding affinity of the short form to PRL thus reducing the level of PRL-related hormone available to the long form. Such increase in binding activity of one receptor after association with another transmembrane protein was shown for the GM-CSF receptor. The GM-CSF receptor ({alpha}) binds with low affinity to the ligand; however, its association with another transmembrane protein (ß) converts the low affinity to high affinity binding (24). Whether PRAP, a developmentally and hormonally regulated protein, acts to prevent the desensitization of the long form of the PRL receptor by affecting the binding affinity of the short form of the PRL or whether it plays an intermediary role in the signaling pathway through the short form of the PRL receptor is not yet known. Defining the role of PRAP in PRL signaling is a challenge for the future.


   Acknowledgments
 
We thank Ms. Linda Alaniz-Avila for photography, Rosemary Clepper for animal care, and Vivian Rogala and Janice Gentry for typing and editorial help.


   Footnotes
 
1 This work was supported by NIH Grants HD-11119 (GG) and Sigma Xi Grant-in-Aid of Research Grant (to W.R.D.). Presented in part at 27th Annual Meeting of Society for the Study of Reproduction, Raleigh, North Carolina, 1992. Back

2 NIH Merit Awardee (HD-11119). Back

Received February 12, 1997.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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M. Risk, A. Shehu, J. Mao, C. O. Stocco, L. T. Goldsmith, J. M. Bowen-Shauver, and G. Gibori
Cloning and Characterization of a 5' Regulatory Region of the Prolactin Receptor-Associated Protein/17{beta} Hydroxysteroid Dehydrogenase 7 Gene
Endocrinology, June 1, 2005; 146(6): 2807 - 2816.
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N. Foyouzi, Z. Cai, Y. Sugimoto, and C. Stocco
Changes in the Expression of Steroidogenic and Antioxidant Genes in the Mouse Corpus Luteum During Luteolysis
Biol Reprod, May 1, 2005; 72(5): 1134 - 1141.
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A. H. Payne and D. B. Hales
Overview of Steroidogenic Enzymes in the Pathway from Cholesterol to Active Steroid Hormones
Endocr. Rev., December 1, 2004; 25(6): 947 - 970.
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Z. Marijanovic, D. Laubner, G. Moller, C. Gege, B. Husen, J. Adamski, and R. Breitling
Closing the Gap: Identification of Human 3-Ketosteroid Reductase, the Last Unknown Enzyme of Mammalian Cholesterol Biosynthesis
Mol. Endocrinol., September 1, 2003; 17(9): 1715 - 1725.
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L. G. Sheffield and J. J. Gavinski
Proteomics Methods for Probing Molecular Mechanisms in Signal Transduction
J Dairy Sci, July 1, 2003; 86(13_suppl): E115 - 124.
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B. Husen, J. Adamski, A. Bruns, D. Deluca, K. Fuhrmann, G. Moller, I. Schwabe, and A. Einspanier
Characterization of 17{beta}-Hydroxysteroid Dehydrogenase Type 7 in Reproductive Tissues of the Marmoset Monkey
Biol Reprod, June 1, 2003; 68(6): 2092 - 2099.
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L. G. Sheffield and J. J. Gavinski
Proteomics methods for probing molecular mechanisms in signal transduction
J Anim Sci, March 1, 2003; 81(suppl_3): 48 - 57.
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M. E. Freeman, B. Kanyicska, A. Lerant, and G. Nagy
Prolactin: Structure, Function, and Regulation of Secretion
Physiol Rev, October 1, 2000; 80(4): 1523 - 1631.
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P. Nokelainen, H. Peltoketo, M. Mustonen, and P. Vihko
Expression of Mouse 17{beta}-Hydroxysteroid Dehydrogenase/17-Ketosteroid Reductase Type 7 in the Ovary, Uterus, and Placenta: Localization from Implantation to Late Pregnancy
Endocrinology, February 1, 2000; 141(2): 772 - 778.
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G. D. Niswender, J. L. Juengel, P. J. Silva, M. K. Rollyson, and E. W. McIntush
Mechanisms Controlling the Function and Life Span of the Corpus Luteum
Physiol Rev, January 1, 2000; 80(1): 1 - 29.
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D. L. Russell and J. S. Richards
Differentiation-Dependent Prolactin Responsiveness and Stat (Signal Transducers and Activators of Transcription) Signaling in Rat Ovarian Cells
Mol. Endocrinol., December 1, 1999; 13(12): 2049 - 2064.
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A. G. Mensah-Nyagan, J.-L. Do-Rego, D. Beaujean, V. Luu-The, G. Pelletier, and H. Vaudry
Neurosteroids: Expression of Steroidogenic Enzymes and Regulation of Steroid Biosynthesis in the Central Nervous System
Pharmacol. Rev., March 1, 1999; 51(1): 63 - 82.
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P. Nokelainen, H. Peltoketo, R. Vihko, and P. Vihko
Expression Cloning of a Novel Estrogenic Mouse 17{beta}-Hydroxysteroid Dehydrogenase/ 17-Ketosteroid Reductase (m17HSD7), Previously Described as a Prolactin Receptor-Associated Protein (PRAP) in Rat
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