1 Departments of Pediatrics,
2 Molecular and Integrative Physiology and
3 Obstetrics and Gynecology, Ralph L. Smith Research Center, University of Kansas Medical Center, Kansas City, Kansas 66160-7338, USA
4 Department of Obstetrics and Gynecology and Physiology, University of Nebraska, Medical Center, Omaha, NE 68198-4515, USA
*Author for correspondence (e-mail: bparia{at}kumc.edu)
Accepted 30 May 2002
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SUMMARY |
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Key words: Uterus, Blastocyst, HB-EGF, ErbB receptor, Implantation, Hamster
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INTRODUCTION |
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Molecular and cellular evidence suggests that HB-EGF, a member of the EGF family of growth factors (Abraham et al., 1993), plays important roles in implantation in several species including humans (reviewed by Paria et al., 2000
; Paria et al., 2001a
). HB-EGF is produced as a transmembrane form, which is proteolytically cleaved to produce the soluble mature form. Both forms of HB-EGF can interact with cell surface proteins of the EGF receptor family (ErbBs) and cell surface heparan sulphate proteoglycan (HSPG) molecules (reviewed by Das et al., 1994
; Elenius et al., 1997
). The Erbb gene family comprises four receptor tyrosine kinase genes: Erbb1, Erbb2, Erbb3 and Erbb4. They share a common structural feature, but differ in their ligand specificity and kinase activity (Carraway and Cantley, 1994
; Heldin, 1995
; Lemke, 1996
). While all of the members of the EGF family can directly bind to ErbB1, HB-EGF, betacellulin and epiregulin act as distinct ligands for ErbB4. ErbB2 and ErbB3 require heterodimerization with either ErbB1 or ErbB4 for intracellular signaling (reviewed by Lim et al., 1998
). Most of the recent work to elucidate the mechanism by which HB-EGF exerts its biological effects has focused on activation of tyrosine phosphorylation of ErbB1. The binding of HB-EGF to the extracellular domain of ErbB1 activates its cytoplasmic tyrosine kinase that phosphorylates the receptor itself (Hunter and Cooper, 1980
). The direct interaction of HB-EGF with ErbB1 plays a crucial role in cell-cell adhesion and signal transmission between neighboring cells. HB-EGF stimulates blastocyst growth and zona hatching in vitro (Das et al., 1994
; Martin et al., 1998
; Mishra and Seshagiri, 2000
; Wang et al., 2000
; Seshagiri et al., 2002
). Furthermore, cells expressing the transmembrane form of HB-EGF adhere to the trophectoderm surface of implantation-competent mouse blastocysts by interacting with ErbB1 or ErbB4 and HSPG molecules displayed on the blastocyst cell surface (Raab et al., 1996
; Paria et al., 1999
). Several studies have shown that uterine expression of HB-EGF is highly relevant to implantation in several species including humans (Das et al., 1994
; Yoo et al., 1997
; Leach et al., 1999
; Yue et al., 2000
). We previously demonstrated that HB-EGF is first induced solely at the site of blastocyst implantation several hours before the onset of the attachment reaction and persists through the early stages of implantation in mice (Das et al., 1994
). This unique uterine HB-EGF expression requires the presence of a blastocyst that gains implantation-competence in the presence of estrogen in the P4-primed uterus (Das et al., 1994
). Although, the presence of immunoreactive HB-EGF has been demonstrated in hamster uterus and blastocyst (Mishra and Seshagiri, 2000
), the expression of Hegfl and its hormonal regulations during implantation are not known in hamsters in which P4 alone, but not estrogen, is sufficient to induce this process. Here we demonstrate that Hegfl is preferentially expressed in the uterine luminal epithelial cells surrounding the blastocysts prior to, during and after the initiation of implantation process. HB-EGF is also expressed in blastocysts and it is a potent inducer of ErbB1 and ErbB4 phosphorylation both in the blastocyst and uterus.
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MATERIALS AND METHODS |
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Implantation occurs without delay in hamsters ovariectomized or hypophysectomized on day 2 of pregnancy and given P4 daily (Prasad et al., 1960; Orsini and Meyer, 1962
; Harper et al., 1969
). This suggests that implantation in hamsters is P4 dependent. However, it is possible that implantation occurred with correct expression of implantation-specific genes because basal levels of estrogen still persisted. To address this issue, a group of pregnant hamsters were hypophysectomized on day 2 (0900 hours) and given P4 (1 mg/hamster) on either day 3 or days 3 and 4. Control hamsters underwent sham operations and were injected with oil. Whole uteri were collected on the morning of day 4 (0900 hours). Implantation sites, determined by blue dye injection, were collected on the evening of day 4 (1600 hours) and the morning of day 5 (0900 hours) for in situ hybridization. Blood samples were also collected to obtain sera for the measurement of circulating estradiol-17ß (E2) levels. Serum E2 levels were measured as described previously using a standard curve ranging from 2-1000 pg/tube (Roy and Greenwald, 1987
).
To determine the effects of steroid hormones on uterine Hegfl expression, hamsters were ovariectomized without regard to their stages of the estrous cycle and rested for 12 days. One group of these hamsters was treated with a subcutaneous injection of P4 (500 µg/hamster), E2 (1.0 µg/hamster) or E2 plus P4. All steroids were dissolved in sesame oil. Hamsters were killed at 2, 6, 12 and 24 hours after injection of hormones and uteri were collected for RNA extraction and in situ hybridization. In the second group, each hamster received an injection of 0.01, 0.10 or 1.0 µg E2 to determine the minimum amount of E2 required for the induction of Hegfl. The third group of hamsters each received an injection of ICI-182,780 (1 mg/hamster) 30 minutes before an injection of 1.0 µg E2 to determine whether nuclear ER mediated the estrogen effects. Animals from the second and third groups were killed 2 or 6 hours after the injection of E2. Uteri were processed for in situ hybridization.
For collection of preimplantation embryos, females having a regular 4-day estrous cycle were superovulated by intraperitonial injection of 20 IU of pregnant mare serum gonadotrophin (PMSG) before 0900 hours on the day of the post-estrous discharge and were mated 3 days later (Kane and Bavister, 1988). Oviducts were flushed at 0900 hours on days 1 and 2 and at 0200 hours on day 3 to collect one-cell, two-cell and four-cell embryos, respectively. Eight-cell/morula stage embryos were collected at 1700 hours on day 3 and blastocysts at 0800 hours on day 4 by flushing uteri. Embryos were washed several times to avoid any contamination of maternal cells in Hamster embryo culture medium-2 (HECM-2) (Ain and Seshagiri, 1997
). An average of 40 to 70 embryos were recovered from each superovulated female. One hundred embryos at each developmental stage were quickly frozen in a small volume of medium in a sterile 1.5 ml microcentrifuge tube for total RNA isolation. Blastocysts were also collected for immunofluorescence, and HB-EGF-stimulated EGFR autophosphorylation studies.
Total uterine RNA preparation
Uterine RNA was extracted using TRIZOL reagent (Gibco Life technologies, USA) according to the manufacturers instruction. In brief, tissues were homogenized in TRIZOL reagent (1 ml/50 mg tissue). Homogenates were mixed with 0.2 ml of chloroform/ml of TRIZOL, shaken vigorously for 15 seconds and centrifuged at 12,000 g for 15 minutes at 4°C. The aqueous phase was collected and added with isopropyl alcohol (0.5 ml/ml TRIZOL reagent) for precipitation of RNA. After 10 minutes at room temperature, samples were again centrifuged to re-precipitate RNA. The precipitated RNA was mixed with 75% ethanol in TRIZOL for washing and centrifuged at 7,500 g to obtain final RNA pellet.
Total embryo RNA preparation
Total RNA from preimplantation embryos was extracted as previously described (Andrews et al., 1991; Paria et al., 1993b
). After addition of E. coli rRNA (20 µg) as a carrier in each tube, total RNA was extracted using sodium dodecyl sulphate/phenol/chloroform buffers. Percentage recovery of total RNA using this method is approximately 59-61% as determined by recovery of a labeled tracer RNA.
RNA probes
Linearized plasmids bearing hamster cDNAs were transcribed using appropriate RNA polymerases to generate sense and antisense probes and labeled with either 32P or 35S for Northern or in situ hybridizations, respectively (Das et al., 1994). A partial clone of rpL7 cDNA was also used as a template for the synthesis of 32P-labeled antisense cRNA probe. All labeled sense and antisense cRNA probes had specific activities of approximately 2x109 dpm/µg.
Northern blot hybridization
Total RNA (6 µg) was denatured and separated by formaldehyde/agarose gel electrophoresis, transferred to nylon membranes and UV cross-linked. Northern blots were prehybridized, hybridized, and washed at 68°C as described previously (Das et al., 1994). Quantitation of hybridized bands was analyzed by densitometric scanning.
In situ hybridization
The protocol followed was as described by Das et al. (Das et al.1994). Briefly, uterine cryosections were mounted onto poly-L-lysine-coated slides and fixed in cold 4% paraformaldehyde solution in phosphate-buffered saline (PBS) for 15 minutes. After prehybridization, sections were hybridized with 35S-labeled sense or antisense probes at 45°C for 4 hours in 50% formamide hybridization buffer. After hybridization and washing, sections were treated with RNase A (20 µg/ml) at 37°C for 20 minutes. RNase A-resistant hybrids were detected by autoradiography using Kodak NTB-2 liquid emulsion (Eastman Kodak Company, Rochester, NY). The slides were poststained with Hematoxylin and Eosin. Sections hybridized with the sense probes served as negative controls.
Analysis of Hegfl, Erbb1 and Erbb4 mRNAs in preimplantation embryos and day 4 uteri
To examine the expression of Hegfl, Erbb1 and Erbb4 mRNAs in preimplantation embryos and day 4 uteri, RT-PCR was employed using isolated total RNAs. Uterine total RNA (1 µg) and 25% of the embryonic total RNA were used for RT reaction using random oligonucleotide primers according to the Manufacturers instruction (Invitrogen, Carlsbad, CA). One-third of the RT product was PCR amplified using sense and antisense primers that were designed from the cloned sequences of the hamster genes, except for ribosomal protein L7 (Rpl7), a house keeping gene. Sense and antisense primers for Rpl7 were designed from mouse Rpl7 sequence (GenBank accession no. M29016), while sense-internal primers used for Southern hybridization was designed from cloned sequence of hamster Rpl7 (GenBank accession no. AF394540). The GenBank accession number for the hamster Hegfl sequence is AF327896 (Table 1).
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Immunodetection of HB-EGF, ErbB1 and ErbB4 in blastocysts
Blastocysts were fixed in 3.7% formaldehyde in PBS at room temperature for 30 minutes, permeabilized in 2.5% Tween 20 in PBS for 5 minutes and then incubated overnight at 4°C with goat polyclonal antibodies to HB-EGF (2 µg/ml) or rabbit polyclonal antibodies to ErbB1 and ErbB4 at a dilution of 1:1000 in PBS. Goat anti-human HB-EGF antibody and rhHB-EGF were obtained from R&D systems, Minneapolis, MN. Rabbit polyclonal antibodies to mouse liver ErbB1 was kindly provided by Eileen Adamson, La Jolla Cancer research Foundation (La Jolla, CA). A mouse monoclonal anti-human ErbB1 and its blocking peptide were purchased from ICN (Costa Mesa, CA). The rabbit polyclonal antibody to mouse ErbB4 and its blocking peptide were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Blastocysts incubated with either non-immune sera or antibodies preneutralized with 200-fold molar excess of the antigenic proteins or peptides served as negative controls. After several washes with PBS containing 0.5% Triton X-100 and 0.5% bovine serum albumin (BSA), blastocysts were incubated with TRITC-labeled rabbit anti-goat antibody or TRITC-labeled goat anti-rabbit antibody (Zymed Laboratories, San Francisco, CA) for 1 hour at room temperature. Nuclei were labeled with Hoechst 33,342 (1 µg/ml; Molecular Probes, Eugene, OR) for 30 minutes at room temperature. After several washes with PBS containing 0.1% BSA, blastocysts were mounted, antigen labeled with TRITC (red) and nuclei stained with Hoechst (blue). They were then viewed in a Zeiss LSM 510 confocal scanning laser microscope (Axioplan 2 Imaging) using excitation wavelengths of 543 nm and 364 nm, respectively. Images shown in the Results section are representative of at least 8 blastocysts from different animals that produced similar patterns.
Autophosphorylation and immunoprecipitation of ErbBs in the uterus and blastocyst
Day 4 blastocysts (0800 hours) collected in groups of 100 were placed in microfuge tubes containing 10 µl of buffer A [10 mM Tris-HCl (pH 7.4), 0.25 M sucrose, 1 mM ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA), 10 µg/ml leupeptin, 10 µg/ml aprotinin and 20 µg/ml phenylmethanesulfonyl fluoride (PMSF)] and sonicated. Membranes from day-4 uteri were prepared as previously described (Das et al., 1994). In brief, day-4 pregnant uteri were homogenized in buffer A and centrifuged at 900 g for 10 minutes at 4°C. The supernatant was centrifuged at 144,000 g for 1 hour at 4°C. The pellet was resuspended again in buffer A and subjected to recentrifugation for 1 hour. The resultant pellet was resuspended in buffer B (10 mM Tris-HCl (pH 7.4), 0.15 mM NaCl, 1 mM EGTA, 10 µg/ml leupeptin, 10 µg/ml aprotinin and 20 µg/ml PMSF).
Blastocyst homogenates and uterine membranes were suspended in 50 µl of phosphorylation buffer (50 mM Pipes (pH 7.0), 1 mM MnCl2, 0.1 mM sodium vanadate) and preincubated with or without HB-EGF (100 ng/ml) for 10 minutes at 4°C. The labeling reactions were performed for 2 minutes at 4°C after addition of 5 µCi [-32P]ATP (1 µM) in the presence of 0.1% Triton X-100. The reaction was terminated by the addition of equal volume of 10% trichloroacetic acid (TCA). To further confirm that HB-EGF induces autophosphorylation of ErbB1 and ErbB4, radiolabeled phosphorylated products were subjected to immunoprecipitation using antibodies to ErbB1 or ErbB4. Trichloroacetic acid (10%)-precipitated phosphorylated products, after washing in 50 mM Tris-HCl (pH 8.0), were resuspended in 100 µl of 50 mM Tris buffer (pH. 8.0). An equal volume of protein A sepharose-antibody conjugates (3 mg:0.8 µg) was added to the mixture. A mouse monoclonal anti-human ErbB1 and a rabbit polyclonal antibody to mouse ErbB4 were purchased from ICN (Costa Mesa, CA) and Santa Cruz Biotechnology (Santa Cruz, CA), respectively. In a separate set of experiments, specificity of these antibodies was confirmed by western blotting using day-4 hamster uterine membranes and preneutralized antibodies with 500-fold excess of the antigenic peptides (data not shown). These reaction mixtures were incubated for 90 minutes at 4°C with constant shaking. The protein A sepharose antibody and antigen complexes were subjected to repeated washes in 10 mM Tris-HCl (pH 8.0). The resultant pellets were boiled in 1x SDS sample buffer for 5 minutes and centrifuged. The supernatants were subjected to 6% SDS-PAGE in parallel with molecular mass markers. The gel was transferred to Immuno-BlotTM PVDF membrane (BIO-RAD, Hercules, CA) and radioactive products were visualized by autoradiography.
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RESULTS |
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The results demonstrate that HB-EGF indeed induces autophosphorylation of ErbB1 and ErbB4 in the day-4 uterus (ErbB1: Fig. 9A, lane 2; ErbB4: Fig. 9B, lane 2) and blastocyst (ErbB1: Fig. 9A, lane 6; ErbB4: Fig. 9B, lane 6). Mouse day-4 uterine membranes were used as controls (ErbB1: Fig. 9A, lane 4; ErbB4: Fig. 9B, lane 4). The total protein content of a mouse blastocyst is about 20 ng (Brinster, 1973), but it is unknown for hamster blastocysts. We assume that the total protein content of hamster blastocysts would be similar to mouse blastocysts or even lower, since cell numbers in hamster blastocysts are lower than those in mice blastocysts (Seshagiri et al., 2002
). Thus, efficient phosphorylation of ErbB1 and ErbB4 by HB-EGF in extracts of 100 hamster blastocysts compared with the use of 45 µg of isolated uterine membrane protein suggests that blastocyst ErbBs are remarkably active in response to HB-EGF signaling.
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DISCUSSION |
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The expression of Hegfl and its cognate receptors ErbB1 and ErbB4 in both the luminal epithelium and blastocyst suggests a dual site of action of this growth factor. The autophosphorylation of these uterine and blastocyst receptors by HB-EGF provides evidence that HB-EGF signaling via these receptors is operative during implantation. It should be noted that the signaling of the EGF family growth factors requires heterodimerization among ErbB isoforms (reviewed by Lim et al., 1998). Thus, it is possible that in addition to ErbB1 and ErbB4, other isoforms also participate in signaling by HB-EGF. However, the greater magnitude of phosphorylation of blastocyst receptors advocates a preferential role of HB-EGF toward embryonic functions. The potentiation of embryonic growth and functions by HB-EGF is also evident in other species including mice, hamsters and humans (Das et al., 1994
; Martin et al., 1998
; Mishra and Seshagiri, 2000
; Wang et al., 2000
; Seshagiri et al., 2002
). However, the source of HB-EGF that influences embryonic function is not clearly understood. It is possible that HB-EGF produced by the blastocyst influences its own functions in an autocrine or juxtacrine manner, since ErbB1 and ErbB4 are displayed on blastocyst cell surface. Alternatively, uterine HB-EGF influences blastocyst functions in a paracrine manner or directs blastocyst homing into the uterus by a juxtacrine manner. The role of soluble and transmembrane HB-EGF in these processes has been documented in mice (Raab et al., 1996
; Paria et al., 1999
). HB-EGF may also be involved in uterine functions that are important for embryo-uterine signaling during implantation. Our findings of dual sites of HB-EGF synthesis and action show diversification of specific gene functions in a physiologically relevant system. We have recently shown that transfer of blastocyst-size affigel blue beads pre-soaked in HB-EGF into uterine lumens of pseudopregnant mice elicit implantation-like responses with appropriate gene expression in the uterus similar to those observed in the presence of living embryos (Paria et al., 2001b
). This observation shows that HB-EGF is locally active to influence uterine and embryonic functions relevant to implantation. In this respect, deletion of the Hegfl gene is warranted to establish the importance of this molecule in embryo development and implantation.
In conclusion, the expression of HB-EGF in the uterus and embryos of various species with different hormonal requirements for implantation underscores the importance of HB-EGF in this process. Particularly, the hamster serves as an intriguing model to study gene regulation and functions during implantation because of its exclusive dependence on P4 during implantation.
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ACKNOWLEDGMENTS |
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REFERENCES |
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Abraham, J. A., Damm, D., Bajardi, A., Miller, J., Klagsbrun, M. and Ezekowitz, R. A. B. (1993). Heparin-binding EGF-like growth factor: Characterization of rat and mouse cDNA clones, protein domain conservation across species, and transcript expression in tissues. Biochem. Biophys. Res. Comm. 190, 125-133.[Medline]
Ain, R. and Seshagiri, P. B. (1997). Succinate and malate improve development of hamster eight-cell embryos in vitro: confirmation of viability by embryo transfer. Mol. Reprod. Dev. 47, 440-447.[Medline]
Andrews, G. K., Huet-Hudson, Y., Paria, B. C., McMaster, M. T., De, S. K. and Dey, S. K. (1991). Metallothionein gene expression and metal regulation during preimplantation mouse embryo development. Dev. Biol. 145, 13-27.[Medline]
Barnard, J. A., Graves-Dea, R., Pittelkow, M. R., DuBois, R., Cook, P., Ramsey, G. W., Bishop, P. R., Damstrup, L. and Coffey, R. J. (1994). Auto- and cross-induction within the mammalian epidermal growth factor-related peptide family. J. Biol. Chem. 269, 22817-22822.
Brinster, R. L. (1973). Nutrition and metabolism of the ovum, zygote, and blastocyst. In Handbook of Physiology (eds. R. O. Greep and E. B. Astwood), pp. E165-E185. Bethesda: American Physiological Society.
Carraway, K. L., III and Cantley, L. C. (1994). A neu acquaintance for ErbB3 and ErbB4: A role for receptor heterodimerization in growth signaling. Cell 78, 5-8.[Medline]
Carson, D. D., Bagchi, I., Dey, S. K., Enders, A. C., Fazleabas, A. T., Lessey, B. A. and Yoshinaga, K. (2000). Embryo implantation. Dev. Biol. 223, 217-237.[Medline]
Das, S. K., Wang, X.-N., Paria, B. C., Damn, D., Abraham, J. A., Klagsbrun, M., Andrews, G. K. and Dey, S. K. (1994). Heparin-binding EGF-like growth factor gene is induced in the mouse uterus temporally by the blastocyst solely at the site of its apposition: a possible ligand for interaction with blastocyst EGF-receptor in implantation. Development 120, 1071-1083.
Dey, S. K. (1996). Implantation. In Reproductive Endocrinology, Surgery and Technology (ed. E. Y. Adashi, J. A. Rock and Z. Rosenwaks), pp. 421-434. New York: Lippincott-Raven Publishers.
Elenius, K., Allison, G., Das, S. K., Paria, B. C., Dey, S. K. and Klagsbrun, M. (1997). Interaction of heparin-binding EGF-like growth factor with multiple receptors. In EGF Receptor in Tumor Growth and Progression (eds R. B. Lichtner and R. N. Harkins), pp. 45-64. Berlin: Springer.
Geisert, R. D., Zavy, M. T., Moffatt, R. J., Blair, R. M. and Yellin, T. (1990). Embryonic steroids and the establishment of pregnancy in pigs. J. Reprod. Fert. Suppl. 40, 293-305.
George, F. W. and Wilson, J. D. (1978). Estrogen formation in the early rabbit embryo. Science 199, 200-201.[Medline]
Giannina, T., Butler, M., Popick, F. and Steinetz, B. G. (1971). Comparative effect of some steroidal and nonsteroidal antifertility agents in rats and hamsters. Contraception 3, 347-359.[Medline]
Harper, M. J. K., Dowd, D. and Elliot, A. S. W. (1969). Implantation and embryonic development in the ovariectomized-adrenalectomized hamster. Biol. Reprod. 1, 253-257.[Medline]
Heap, R. B., Flint, A. P. F. and Gadsby, J. E. (1981). Embryonic signals and maternal recognition. In Cellular and Molecular Aspects of Implantation (eds S. R. Glasser and D. W. Bullock), pp. 311-325. New York: Plenum Press.
Heldin, C. H. (1995). Dimerization of cell surface receptors in signal transduction. Cell 80, 213-223.[Medline]
Hoversland, R. C., Dey, S. K. and Johnson, D. C. (1982). Aromatase activity in the rabbit blastocyst. J. Reprod. Fert. 66, 259-263.[Abstract]
Howell, A., Osborne, C. K., Morris, C. and Wakeling, A. E. (2000). ICI 182,780 (FaslodexTM):Development of a novel, "pure" antiestrogen. Cancer 89, 817-825.[Medline]
Hunter, T. and Cooper, J. A. (1980). Epidermal growth factor rapid tyrosine phosphorylation of proteins in A431 human tumor cells. Cell 24, 741-752.
Kane, M. T. and Bavister, B. D. (1988). Vitamin requirements for development of eight-cell hamster embryos to hatching blastocysts in vitro. Biol. Reprod. 39, 1137-1143.[Abstract]
Leach, R. E., Khalifa, R., Ramirez, N. D., Das, S. K., Wang, J., Dey, S. K., Romero, R. and Armant, D. R. (1999). Multiple roles for heparin-binding epidermal growth factor-like growth factor are suggested by its cell-specific expression during the human endometrial cycle and early placentation. J. Clin. Endocrinol. Metab. 84, 3355-3363.
Lemke, G. (1996). Neuregulins in development. Mol. Cell. Neurosci. 7, 247-262.[Medline]
Lim, H., Das, S. K. and Dey, S. K. (1998). ErbB genes in the mouse uterus: cell-specific signaling by epidermal growth factor (EGF) family of growth factors during implantation. Dev. Biol. 204, 97-110.[Medline]
Martin, K. L., Barlow, D. H. and Sargent, I. L. (1998). Heparin-binding epidermal growth factor significantly improves human blastocyst development and hatching in serum-free medium. Hum. Reprod. 13, 1645-1652.[Abstract]
Mishra, A. and Seshagiri, P. B. (2000). Heparin binding-epidermal growth factor improves blastocyst hatching and trophoblast outgrowth in the golden hamster. Reprod. Biomed. Online 1, 87-95.[Medline]
Orsini, M. W. and Meyer, R. K. (1962). Effects of varying doses of progesterone on implantation in the ovariectomized hamster. Proc. Soc. Exp. Biol. Med. 110, 713-715.
Paria, B. C., Huet-Hudson, Y. and Dey, S. K. (1993a). Blastocysts state of activity determines the "window" of implantation in the receptive mouse uterus. Proc. Natl. Acad. Sci. USA 90, 10159-10162.[Abstract]
Paria, B. C., Das, S. K., Andrews, G. K. and Dey, S. K. (1993b). Expression of the epidermal growth factor receptor gene is regulated in mouse blastocysts during delayed implantation. Proc. Natl. Acad. Sci. USA 90, 55-59.[Abstract]
Paria, B. C., Elinius, K., Klagsbrun, M. and Dey, S. K. (1999). Heparin-binding EGF-like growth factor interacts with mouse blastocysts independently of ErbB1: a possible role for heparan sulfate proteoglycans and ErbB4 in blastocyst implantation. Development 126, 1997-2005.
Paria, B. C., Lim, H., Das, S. K., Reese, J. and Dey, S. K. (2000). Molecular signaling in uterine receptivity for implantation. Sem. Cell. Dev. Biol. 11, 1-8.[Medline]
Paria, B. C., Song, H. and Dey, S. K. (2001a). Implantation: molecular basis of embryo-uterine dialogue. Int. J. Dev. Biol. 45, 597-605.[Medline]
Paria, B. C., Ma, W., Tan, J., Raja, S., Das, S. K., Dey, S. K. and Hogen, B. L. (2001b). Cellular and Molecular responses of the uterus to embryo implantation can be elicitated by locally applied growth factors. Proc. Natl. Acad. Sci. USA 98, 1047-1052.
Prasad, M. R. N., Orsini, M. W. and Meyer, R. K. (1960). Nidation in progesterone-treated estrogen-deficient hamsters, Mesocricetus auratus (Waterhouse). Proc. Soc. Exp. Biol. Med. 104, 48-51.
Psychoyos, A. (1973). Endocrine control of egg implantation. In Handbook of Physiology (eds R. O. Greep, E. G. Astwood and S. R. Geiger), pp. 187-215. Washington, DC: American Physiological Society.
Raab, G., Kover, K., Paria, B. C., Dey, S. K., Ezzell, R. M. and Klagsbrun, M. (1996). Mouse preimplantation blastocysts adhere to cells expressing the transmembrane form of heparin-binding EGF-like growth factor. Development 122, 637-645.
Roy, S. K. and Greenwald, G. S. (1987). In vitro steroidogenesis by primary to antral follicles in the hamster during the periovulatory period: effects of follicle-stimulating hormone, luteinizing hormone, and prolaction. Biol. Reprod. 37, 39-46.[Abstract]
Sengupta, J., Paria, B. C. and Manchanda, S. K. (1981). Effect of an estrogen antagonist on implantation and uterine leucylnaphthylamidase activity in the ovariectomized hamster. J. Reprod. Fert. 62, 437-440.[Abstract]
Seshagiri, P. B., McKenzie, D. I., Bavister, B. D., Milliamson, J. L. and Aiken, J. M. (1992). Golden hamster embryonic genome activation occurs at the two-cell stage: correlation with major developmental changes. Mol. Reprod. Dev. 32, 229-235.[Medline]
Seshagiri, P. B., Mishra, A., Ramesh, G. and Rao, R. P. (2002) Regulation of peri-attachment embryo development in the golden hamster: role of growth factors. J. Reprod. Immun. 53, 302-213.
Stromstedt, M., Keeney, D. S., Waterman, M. R., Paria, B. C. and Dey, S. K. (1996). Preimplantation mouse blastocysts fail to express CYP genes required for estrogen synthesis. Mol. Reprod. Dev. 43, 428-436.[Medline]
Wang, X.-N., Das, S. K., Damm, D., Klagsbrun, M., Abraham, J. A. and Dey, S. K. (1994). Differential regulation of heparin-binding epidermal growth factor in the adult ovariectomized mouse uterus by progesterone and estrogen. Endocrinology 135, 1264-1271.[Abstract]
Wang, J., Mayernik, L., Schultz, J. F. and Armant, D. R. (2000). Acceleration of trophoblast differentiation by heparin-binding EGF-like growth factor is dependent on the stage-specific activation of calcium influx by ErbB receptors in developing mouse blastocysts. Development 127, 33-44.
Watson, A. J. and Barcroft, L. C. (2001). Regulation in blastocyst formation. Front. Biosci. 6, d708-d730.[Medline]
Yoo, H. J., Barlow, D. H. and Mardon, H. J. (1997). Temporal and special regulation of expression of heparin-binding epidermal growth factor-like growth factor in the human endometrium: a possible role in blastocyst implantation. Dev. Genet. 21, 102-108.[Medline]
Yue, Z. P., Yang, Z. M., Li, S. J., Wang, H. B. and Harper, M. J. (2000). Epidermal growth factor family in rhesus uterus during the menstrual cycle and early pregnancy. Mol. Reprod. Dev. 55, 164-174.[Medline]
Zhang, Z., Funk, C., Glasser, S. R. and Mulholland, J. (1994). Progesterone regulation of heparin-binding epidermal growth factor-like growth factor gene expression during sensitization and decidualization in the rat uterus: effects of the antiprogestin, ZK 98,299. Endocrinology 135, 1256-1263.[Abstract]