Characteristics of an oviductal glycoprotein and its potential role in fertility control

At the time of ovulation the lining epithelium of the mammalian oviduct consists of columnar ciliated and secretory cells. These mature cells are dependent on ovarian steroids in carnivores. Oestradiol induces differentiation of these cells and maintains their mature functional state, and progesterone induces dedifferentiation. The secretory cells synthesize and secrete an oestrogen-dependent high molecular weight glycoprotein. The cDNAs encoding oviductal glycoproteins from several species have been sequenced and show high similarity. The human cDNA hybridized with a single message on northern blots of total oviduct RNA obtained from oestradiol-treated cats (about 2.3 kb) and dogs (about 2.1 kb). This glycoprotein is the major nonserum protein present in the oviductal lumen at the time of ovulation, fertilization and early embryonic development. The glycoproteins associate with the zona pellucida of oviductal eggs in all species studied to date. Recent studies suggest that the bovine glycoprotein facilitates sperm capacitation and significantly increases the ability of bovine spermatozoa to fertilize bovine oocytes in vitro, that the hamster glycoprotein increases the sperm penetration rate of the zona pellucida by three times and that the human glycoprotein increases sperm binding to the zona pellucida by three times. All of the evidence for a biological function for this glycoprotein is derived from studies performed in several different species at reproductive stages before fertilization. The biological actions of this glycoprotein suggest a potential role for the glycoprotein in fertility control. Specifically, purified or recombinant glycoprotein may improve success in IVF procedures by enhancing binding of spermatozoa to the zona pellucida and improving fertilization rates. The glycoprotein may also be a potential immunocontraceptive target since antibodies generated against the oviductal glycoprotein may prevent fertilization by preventing binding of spermatozoa to the zona pellucida.

The baboon oviduct: characteristics of an oestradiol-dependent oviduct-specific glycoprotein

The baboon oviductal epithelium differentiates into a tall columnar epithelium consisting of ciliated and secretory cells during the follicular phase of the menstrual cycle in response to rising oestradiol levels. The apical tips of these secretory cells are filled with membrane-bound secretory granules. During the luteal phase when progesterone levels are elevated, the epithelium regresses and deciliation occurs. Analysis of secretory proteins obtained from explant culture media by SDS-PAGE followed by fluorography or Western blots has revealed that the baboon oviduct synthesizes and secretes a high molecular weight glycoprotein during the follicular phase of the cycle. Immunocytochemistry demonstrated that this oviductal glycoprotein is localized to the secretory granules of epithelial secretory cells, is oviduct specific, and that following secretion the oviductal glycoprotein binds to the zona pellucida and perivitelline space of ovulated oocytes and embryos within the oviduct. Similar proteins have been characterized in other mammalian species. cDNA data show that the complete coding sequence is 2228 bp for a protein of 623 amino acids. A Genbank search showed that baboon oviductal glycoprotein has high homology to other oviductal glycoprotein sequences at both the nucleotide and amino acid levels. Studies conducted to date probing the biological function of oviductal glycoprotein indicate that this protein plays a role in prefertilization reproductive events (sperm capacitation; sperm-zona binding; zona penetration). Additional experiments are needed to reveal a specific function and mechanism for this molecule.

Secretory proteins of the baboon (Papio anubis) endometrium: regulation during the menstrual cycle and early pregnancy

The biological function of uterine endometrial secretory proteins in the primate remain to be elucidated. In general, during the luteal phase and under progesterone dominance, the glandular epithelial cells synthesize and secrete a number of proteins. Of these, placental protein 14 (PP14; now referred to as glycodelin) and insulin-like growth factor binding protein-1 (IGFBP-1) are the best characterized. Although induced by progesterone, their synthesis increases exponentially during pregnancy. In the baboon, glycodelin is immunolocalized to the mid functionalis and basal glands between days 10 and 12 post-ovulation. In response to either exogenous or blastocyst-secreted chorionic gonadotrophin, glandular synthesis increases markedly and remains elevated up to days 18-25 of pregnancy. The decrease in glycodelin in the endometrium is associated with glandular regression during the first third of pregnancy. In contrast, IGFBP-1 is only observed in the deep basal glands during the luteal phase. Following the establishment of pregnancy, IGFBP-1 synthesis switches from glandular to stromal and is correlated with the process of decidualization. IGFBP-1 synthesis continues to increase throughout gestation. We propose that glycodelin may have immunosuppressive properties and that IGFBP-1 may regulate trophoblast migration within the uterine endometrium.

The progressive rise in the expression of alpha crystallin B chain in human endometrium is initiated during the implantation window: modulation of gene expression by steroid hormones

Human endometrium undergoes sequential changes during the menstrual cycle and becomes receptive to implantation during a defined period in the secretory phase. We attempted to identify the genes expressed during this period by representational difference analysis (RDA). When the cDNAs of a proliferative endometrium were used as the driver and the cDNAs of a post-ovulatory day 5 endometrium were used as the tester, a number of bands were identified by RDA. DNA of the cloned RDA products revealed that the majority of the clones contained a fragment of a cDNA identical to that of a crystallin B chain. Northern blot analysis showed that the expression of the alpha crystallin B chain mRNA was absent during the proliferative phase. The expression of the mRNA of alpha crystallin B chain first appeared in the secretory phase, progressively increased during this phase and peaked in the late secretory endometria. The pattern of expression of alpha crystallin B chain mRNA in the endometrium of mature cycling baboons (Papio anubis) was similar to that seen in human endometrium. As revealed by Western blot analysis, the expression of the alpha crystallin B chain protein in human endometrium followed a pattern of expression similar to its mRNA. At the cellular level, the immunoreactive protein first appeared in the surface epithelial cells of human endometrium within the implantation window without significant immunoreactivity in the underlying glandular cells. During the mid- and late secretory phases, the intensity of staining in the epithelial cells was enhanced and an intense immunoreactivity was developed in the glandular epithelium, alpha crystallin B chain was virtually an epithelial product and no immunoreactivity for this protein was detectable in the stromal cells, endothelial cells or lymphoid cells. The expression of alpha crystallin B chain could be regulated, by medroxy progesterone acetate as well as by oestrogen withdrawal, in human endometrial carcinoma cells (EnCa-101), transplanted to nude mice. Based on the data presented here, the known function of alpha crystallin B chain and its distinct pattern of expression in human endometrium, we suggest that this protein is an important factor within the molecular repertoire that makes endometrium receptive to implantation.

Expression of steroid receptors and steroidogenic enzymes in the baboon (Papio anubis) corpus luteum during the menstrual cycle and early pregnancy

As estrogen and progesterone are proposed regulators of luteal function, this study was undertaken to correlate the presence of receptors for these steroids with luteal function during early pregnancy. Corpora lutea (CL) were obtained from nonpregnant baboons during the midluteal [ML; days 7-8 postovulation (PO)] and late luteal (LL: days 11-12 PO) phases of the menstrual cycle or from pregnant baboons on days 18, 25, 29, or 31-33 PO. Estrogen and progestin receptors (ER and PR, respectively) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) were detected by immunocytochemistry using specific monoclonal (H222 for ER; JZB39 for PR) or polyclonal (S683 for 3 beta HSD) antibodies. In addition, ribonucleic acid (RNA) was extracted from CL, processed for Northern blot analysis, and probed with complementary DNAs to human PR, human 3 beta HSD, and rat aromatase. Levels of messenger RNA (mRNA) for 3 beta HSD were quantified by laser densitometric scanning, and the data were normalized to the expression of a housekeeping gene (glyceraldehyde-3-phosphate dehydrogenase) to correct for loading differences. CL did not demonstrate specific nuclear, stain for ER at any stage of the menstrual cycle or pregnancy. In contrast, PR-positive cells were present during the ML phase, but decreased during the LL phase (P < 0.05). PR-positive cells were maintained during early pregnancy at levels comparable to the ML phase (P < 0.05). Staining for 3 beta HSD was present at all stages of the cycle and pregnancy. Although the percent of 3 beta HSD-positive cells appeared to decrease as pregnancy proceeded, this was not statistically different (P > 0.05). The complementary DNA to PR hybridized to multiple transcripts (approximately 4.4, 3.1, 1.6, and 0.95 kilobases) in CL of the cycle. A single transcript (approximately 1.8 kilobases) for 3 beta HSD was present in CL at all stages of the cycle and pregnancy. The level of 3 beta HSD mRNA was highest during the ML phase and declined significantly (P < 0.05) during the LL phase and early pregnancy. Three transcripts (approximately 3.6, 3.0, and 1.7 kilobases) for aromatase were detected in CL of the cycle and pregnancy. Aromatase mRNA increased during early pregnancy. These results support the concept of PR-mediated events, but not ER-regulated processes in the primate CL. Further-more, the data suggest that the steroidogenic enzymes 3 beta HSD and aromatase are differentially regulated during early pregnancy.

Distribution of integrins and the extracellular matrix proteins in the baboon endometrium during the menstrual cycle and early pregnancy

Integrins are heterodimeric glycoproteins that have been found to undergo dynamic temporal and spatial changes in distribution in the endometrium during the menstrual cycle in women. Likewise the extracellular matrix (ECM) ligands for these receptors are likely to play a role in the establishment of a receptive endometrium. To develop primate models to study the role of these molecules in the cascade of molecular events leading to implantation, integrin expression and associated changes in ECM were investigated during the menstrual cycle and in early pregnancy in the baboon. Antibodies specific for the integrins (alpha(1-6) and alpha(v); beta1, beta3, and beta4) and ECM (laminin, collagen IV, fibronectin) were utilized. In addition, cytokeratin and alpha-smooth muscle actin were used as epithelial, stromal, and smooth muscle cell markers, respectively. Endometrium was obtained in duplicate or triplicate during the menstrual cycle and early pregnancy. Changes observed during the natural menstrual cycle were confirmed using ovariectomized, steroid-treated animals. Constitutively expressed integrins on the endometrial epithelium included the collagen/laminin receptors: alpha2, alpha3, alpha6, and beta4. The pattern of expression correlated well with the distribution of ECM in this tissue. Collagen IV was confined to the basement membrane of glandular epithelium and blood vessels. Laminin immunostaining was found in the basement membrane, mostly in the stroma of the basal region, in the glandular endometrium and vasculature. Fibronectin was present throughout the stroma but not in the basement membrane. The collagen receptor alpha1 beta1 and fibronectin receptor alpha4 beta1 appeared in the glandular epithelium in the luteal phase. As in the human, alpha1 and alpha4 disappeared from the glandular epithelium with the establishment of pregnancy. In contrast, the alpha4 beta3 vitronectin receptor appeared in the glandular epithelium only in pregnancy or following long-term steroid treatment with estrogen and progesterone but not during the time of uterine receptivity associated with the initial period of embryo attachment. Osteopontin, an ECM ligand for alpha(v) beta3, was coexpressed with this integrin in invading cytotrophoblasts, glandular epithelium, and decidualizing stromal cells. Decidualization in the baboon was associated with changes in integrin expression similar to those found in humans: there was an increase in alpha1, alpha3, alpha6, beta1, and alpha(v) beta3 in the decidualized stromal cells. Laminin and collagen IV expression also increased at the implantation site and throughout the endometrium. In contrast, fibronectin expression was most evident at the implantation site and corresponded to alpha5 expression on the invading cytotrophoblasts. In summary, marked similarities were found in the expression of ECM and the integrin receptors between the baboon and the human endometrium throughout the menstrual cycle and in pregnancy. Cycle-specific integrins, alpha1, and alpha4, were present on epithelial cells during the secretory phase. Delayed expression of alpha(v) beta3 in baboon endometrial glands correlated closely with the time of enhanced glandular secretory activity in this primate. The baboon appears to be an excellent model for the investigation of the role of integrins and ECM leading to successful implantation.

Mucin (Muc-1) expression is differentially regulated in uterine luminal and glandular epithelia of the baboon (Papio anubis)

Changes in the organization and composition of apical cell surface glycoconjugates accompany the transition of luminal epithelial cells from the prereceptive state of the uterus in many species. In spite of the biological and clinical significance of this process, few molecular markers have arisen as useful predictors of uterine receptivity. Recent studies in mice demonstrate that the transmembrane mucin glycoprotein, Muc-1, is abundantly expressed at the apical surface of luminal epithelia under most conditions and is invariably reduced in receptive uteri. These and other observations have led to the suggestion that mucins serve an antiadhesive role and function to maintain a nonreceptive uterine state. A pan-species Muc-1 specific antibody recognizing a peptide motif conserved in the cytoplasmic domain of Muc-1 was used to examine the temporal and spatial expression of cell-associated Muc-1 in baboon uteri under a variety of conditions, including the pre- and perimplantation periods. Muc-1 expression was not driven by estrogen influences alone, but required progesterone action. In animals exposed to both steroids, Muc-1 was expressed at low moderate levels in epithelia of the basalis and functionalis regions. The highest expression of Muc-1 was detected in surface epithelium of the preimplantation phase, i.e., up to Day 8 (Day 0 = day of ovulation), or in ovariectomized animals receiving a steroid hormone regime that mimicked this phase (14 days of estrogen priming followed by 7 days of estrogen plus progesterone). Continued exposure to both hormones, i.e., as seen at Days 10-12 or in ovariectomized baboons given 14 days of estrogen plus progesterone treatment after estrogen priming, resulted in marked reduction of Muc-1 expression in the surface epithelium; however, staining patterns in the glandular epithelium were unchanged by this treatment. The expression of Muc-1 on the surface epithelium during the prereceptive phase was associated with the presence of both estrogen and progestin receptors in these epithelia. Muc-1 expression was reduced by neither antiestrogen treatment during the prereceptive stage nor antiprogestin treatment through to the receptive phase. Furthermore, persistent Muc-1 expression in the functionalis and basalis epithelium correlated with expression of progestin receptors. Thus, Muc-1 expression appeared to be progesterone-dependent rather than estrogen-dependent. It is concluded that Muc-1 expression in surface epithelium serves as a marker of the prereceptive phase in the baboon and that loss of Muc-1 from surface epithelium correlates with generation of a receptive uterine state.

Association of oviduct-specific glycoproteins with human and baboon (Papio anubis) ovarian oocytes and enhancement of human sperm binding to human hemizonae following in vitro incubation

The objectives of this study were 1) to determine whether or not human and baboon oviduct-specific glycoproteins (human OGP, baboon OGP) would associate with ovarian oocytes during in vitro incubation in a manner similar to that detected in vivo for oviductal oocytes and 2) to determine whether the association of OGP with ovarian oocytes influenced sperm binding. In vitro association of OGP with ovarian oocytes was assessed by indirect immunofluorescence assay using a polyclonal antibody prepared against human or baboon OGP. Human and baboon ovarian oocytes incubated in culture media containing OGP showed association of OGP with the zona pellucida (ZP) as detected by bright fluorescence. A similar pattern of fluorescence was observed in baboon oviductal oocytes (positive control). No fluorescence of the ZP was detected from ovarian oocytes incubated with culture medium alone. The pattern of fluorescence for ovarian oocytes incubated with OGP and serum albumin, the major oviductal fluid protein, was similar to that for oocytes incubated with OGP alone. A modified hemizona assay was used to assess whether association of human OGP with human ovarian oocytes influenced sperm binding. The number of sperm bound to hemizonae in the presence of human OGP was significantly greater (p < 0.01) than the number bound to hemizonae in the control culture medium. Addition of antibodies specific for human OGP to the incubation medium 1 h prior to addition of gametes blocked the enhancement of sperm binding seen in the presence of human OGP alone. Finally, human hemizona assays conducted in the presence of baboon OGP resulted in a significant decrease (p < 0.05) in the number of sperm bound per zona compared with that in culture medium alone despite high homology between human and baboon OGP. These results 1) suggest that human OGP associates with ovulated oocytes in vivo; 2) support the hypothesis that association of OGP with the ZP may play a role in fertilization, possibly through enhancing the binding of sperm to the ZP within the oviduct; and 3) suggest that a homologous system (i.e., gametes and oviductal glycoprotein from the same species) is necessary for study of the function of oviductal glycoproteins.

Different molecular and messenger ribonucleic acid forms of insulin-like growth factor-binding protein-3 in the pregnant baboon (Papio anubis)

The ratio of the serum concentrations of insulin-like growth factors (IGF) to IGF-binding protein (IGFBP)-3 is highly correlated (Baxter & Martin 1986). During pregnancy in the baboon, this ratio is perturbed; serum IGFBP-3 concentrations increase 10-fold, yet IGF-I levels are unaltered and IGF-II is increased only 2-fold (Giudice et al. 1993). The aims of this study were to determine the molecular distribution of IGFBP-3 and to identify the tissue source and form(s) of IGFBP-3 during pregnancy in the baboon. Serum of non-pregnant and pregnant baboons, and conditioned media of decidua and placental explant cultures were characterized using neutral size-exclusion chromatography in combination with Western ligand blot, Western immunoblot, an IGFBP-3 radioimmunoassay (RIA) and an IGFBP-3 protease assay. Localization of immunoreactive IGFBP-3 was determined by immunocytochemistry, and expression of IGFBP-3 mRNA in the placental and decidual explants was examined by Northern blot analysis. RIA confirmed that immunoreactive IGFBP-3 is increased 10-fold in pregnancy serum compared with non-pregnancy serum. Size-exclusion chromatography combined with an IGFBP-3 RIA revealed that, unlike non-pregnancy serum where 70% of the immunoreactive IGFBP-3 elutes in the 150 kDa ternary complex, equal amounts of immunoreactive IGFBP-3 were measured in pregnancy serum in the < or = 150 and 60 kDa IGFBP regions. Western analysis revealed that non-pregnancy serum contained predominantly a 45-40 kDa IGFBP-3 doublet and a 28 kDa immunoreactive form of IGFBP-3, while in pregnancy serum IGFBP-3 existed as a 45-40 kDa doublet, as well as 26-28 kDa and 18 kDa immunoreactive forms. These alternative forms of IGFBP-3 were not attributable to detectable IGFBP-3 protease activity. To identify the source of the increased serum levels of IGFBP-3 during pregnancy, we examined explant culture media of baboon decidua and placenta. Size-exclusion chromatography combined with RIA and Western analysis revealed that: (1) more immunoreactive IGFBP-3 was produced by decidual cultures than by placental explants, but less 45-40 kDa IGFBP-3 was present in decidua; (2) the immunoreactive forms of IGFBP-3 detected in decidua were similar to those found in maternal serum; (3) placental explants secreted only 45-40 kDa IGFBP-3 in culture. IGFBP-3 was immunohistochemically localized to the cells of placental villi, and to the perinuclear region of the decidual cells and staining for IGFBP-3 was more intense in the decidua than in the placenta. Northern analysis of the explant cultures revealed two IGFBP-3 mRNA transcripts of 2.4 and 1.7 kb in both decidua and placenta which may account for the different immunoreactive forms of IGFBP-3 detected in the baboon. However analysis of non-pregnancy liver also revealed two IGFBP-3 transcripts of 2.4 and 1.7 kb. These data suggest that the two transcripts are not solely pregnancy-associated and levels of protein may be the reason for detection of multiple immunoreactive IGFBP-3 fragments in pregnancy.

A Baboon (Papio anubis) simulated-pregnant model: cell specific expression of insulin-like growth factor binding protein-1 (IGFBP-1), type I IGF receptor (IGF-1 R) and retinol binding protein (RBP) in the uterus

In order to test the hypothesis that the baboon conceptus/placenta regulates the synthesis of specific proteins in the endometrium, we developed a simulated-pregnant baboon model. Baboons (n=2-6/group) were treated with increasing amounts of human chorionic gonadotrophin (hCG) for 10 or 12 days beginning on day 6 or 7 PO. Uterine tissues were obtained at day 18 PO following 12 days of hCG treatment. Animals in the day 25 and 32 PO group were treated for 10 days with hCG. Following the hCG treatment, estradiol (E) and progesterone (P) implants were inserted subcutaneously. Control groups consisted of E and P treatment only (day 25 PO), or ovariectomy on day 6 or 7 PO followed by hCG plus E and P treatment (days 18 and 25 PO). Serum samples were obtained daily or once every 2 days and analysed for E and P by radioimmunoassay. hCG activity in serum was determined by a Leydig cell bioassay. Portions of the endometrial tissue were either subjected to organ explant culture, analysed by immunocytochemistry or extracted for RNA. Peripheral serum levels of hCG, E and P in the experimental groups fell within the 95% confidence interval limits of hormone concentrations achieved during pregnancy. The morphology of the endometrium in the hCG treated baboons and pregnant baboons was similar i.e., distended convoluted glands, many spiral artery beds, a loose vacuolized stroma, and increased collagen staining. However, in the absence of hCG (E+P treatment only) the glands tended to be straight rather than corkscrew-shaped, and decreased stromal vacuolization and collagen staining was evident.(35)S-methionine labeled proteins in explant culture conditioned media (TCM) were analysed by two-dimensional SDS-PAGE and fluorography. A comparable pattern of protein synthesis was apparent in all treatment groups except for a low molecular weight (27 000-30 000 daltons) group of polypetides which only was evident in TCM from the hCG treated baboons. A similar group of proteins are also secreted by the baboon endometrium during pregnancy. The immunocytochemical localization of estrogen (ER) and progesterone receptors (PR) was comparable to that observed in pregnant baboons. IGFBP-1 localization was confined to the glandular epithelium in the hCG treated groups (intact and ovariectomized) and was virtually undetectable in the E and P treated group. The intensity of IGFBP-1 staining was variable within each of the hCG treatment groups on days 18, 25 and 32 PO. This variability was also apparent by Western blot analysis, immunoassay of proteins in TCM and on Northern blots of total RNA from the same animals. In contrast, IGF-I R immunostaining was evident in both glandular and surface epithelium of all treatment groups. Expression of RBP was confined to the basal glands. The characteristic upregulation of RBP synthesis in the functionalis observed during early pregnancy was not apparent in any of the treatment groups. In summary, these studies indicate that exogenous hCG in conjunction with E and P, can induce the general morphological and biosynthetic changes the baboon endometrium undergoes during early pregnancy. In addition, this hormonal treatment is also capable of maintaining the epithelial expression of IGFBP-1, IGF-1 and RBP. However, other factors from the conceptus appear to be necessary to induce the cell specific changes in the expression of these three proteins that are observed during pregnancy.

Smooth muscle myosin II and alpha smooth muscle actin expression in the baboon (Papio anubis) uterus is associated with glandular secretory activity and stromal cell transformation

The objective of this study was to investigate the localization and hormonal regulation of smooth muscle myosin II (SMM II) and alpha smooth muscle actin (alpha SMA) in the baboon uterus, since cytoskeletal proteins are involved in secretory function and morphological transformation. Uterine tissue was obtained from baboons 1) during the menstrual cycle, 2) following steroid treatment of ovariectomized baboons, 3) during pregnancy (Days 14-60 postovulation [PO]), and 4) during simulated pregnancy (Days 18-32 PO). Tissues were processed for immunocytochemical localization of SMM II or alpha SMA with specific polyclonal or monoclonal antibodies, respectively. SMM II stained all smooth muscle cells of blood vessels and myometrium regardless of treatment. Glandular epithelial staining was present only in endometrium obtained during the luteal phase or following estrogen and progesterone treatment. Staining intensity was greater in the basalis than in the functionalis. The number of glands staining positive for SMM II on Days 18-32 of pregnancy and simulated pregnancy was variable. Glandular stain was absent after Day 32 PO. These immunocytochemical data were confirmed by immunoblot analysis of glandular cytosolic extracts. Stromal staining for SMM II was present under the luminal epithelium during simulated pregnancy (Days 18-32), on Day 25 of steroid treatment in the simulated-pregnant controls, and in nonimplantation sites during pregnancy. In contrast, alpha SMA staining was low or absent in all uterine cell types in ovariectomized baboons. Under estrogen-dominated conditions (follicular phase and estrogen treatment), alpha SMA staining was present in smooth muscle cells, and this staining persisted throughout the remaining treatment periods. Glandular epithelial staining for alpha SMA was absent in all treatment groups. However, alpha SMA staining in stromal fibroblasts underneath the luminal epithelium was evident as early as Day 14 of pregnancy and Day 18 of simulated pregnancy. The number of stromal fibroblasts that stained positive increased in the surface region of the functionalis between Days 18 and 32 PO, and the staining extended throughout the upper functionalis region. There was a decrease in the number of positively stained stromal fibroblasts, particularly at the implantation site, between Days 32 and 40 of pregnancy. By Days 50-60 of pregnancy, this staining was almost absent. The induction of alpha SMA in stromal fibroblasts in the functionalis region in pregnant baboons was confirmed by immunoblot analysis of stromal cell cytosol extracts. We conclude that the progesterone-induced glandular expression of SMM II may be involved in uterine secretory function and that alpha SMA expression in stromal fibroblasts during pregnancy and after long-term steroid treatment is associated with the decidualization process.

A human oviduct-specific glycoprotein: synthesis, secretion, and localization during the menstrual cycle

The major objective of this study was to examine the hormonal regulation of a human oviduct-specific glycoprotein (huOGP) throughout the menstrual cycle and in all regions of the human oviduct. Regulation of synthesis and secretion was examined at both the protein (Western immunoblots and immunocytochemistry) and mRNA (Northern and slot blots) levels and correlated with changes in the morphological features of the oviductal epithelial cells throughout the cycle. Immunoblot analysis of oviductal fluid and explant culture media from all regions of the oviduct demonstrated that huOGP is primarily found during the follicular stage of the cycle and is not present in serum, follicular fluid, or uterine endometrium. Moreover, two-dimensional (2-D) immunoblots showed that all major isoelectric variants of huOGP observed on 2-D fluorographs are immunologically related. Light microscopic immunocytochemistry localized huOGP to oviductal secretory cells in both ampulla and isthmic regions, with the most intense immunoperoxidase staining seen in midcycle samples. Using an indirect immunogold technique at the electron microscopic level, huOGP was specifically localized to secretory granules of the ampullary and isthmic nonciliated epithelial cells. The ultrastructural characteristics of these secretory cells during the mid to late follicular phase of the cycle suggested elevated protein synthetic activity. In addition, mRNA expression for huOGP was elevated in all regions of the oviduct in midcycle specimens. Collectively, these data indicate that huOGP is a major tissue-specific, stage-specific secretory product of the human oviduct during the periovulatory stage of the cycle and support the hypothesis that huOGP synthesis and secretion may be regulated by fluctuations in the levels of estrogen and progesterone.

Secretory proteins and growth factors of the baboon (Papio anubis) uterus: potential roles in pregnancy

The primate endometrium undergoes distinct morphological changes during the menstrual cycle. These alterations are regulated by the steroid hormones, estrogen and progesterone. Several lines of evidence suggest that some of these hormonally induced changes may be modulated by growth factors. Our studies have focused on characterizing the secretory activity of the uterine endometrium associated with these hormonally regulated morphological changes during the menstrual cycle and pregnancy in the baboon. Additionally, we have also attempted to study the regulation of specific growth factors and their receptors. In this review we present evidence to indicate that growth factor receptors for insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF), and secretory proteins, insulin-like growth factor binding protein-1 (IGFBP-1) and retinol binding protein (RBP), which are present in the glandular epithelium during the menstrual cycle, undergo cell-specific changes in gene expression at the implantation site during pregnancy. We postulate that these alterations in growth factor receptor and secretory protein expression are conceptus modulated and may play important regulatory roles during trophoblast invasion and decidualization.

Epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor localization in the baboon (Papio anubis) uterus during the menstrual cycle and early pregnancy

OBJECTIVE

Marked alterations occur in the synthesis of endometrium-specific proteins during the first third of pregnancy in the baboon. Because epidermal growth factor (EGF) expression has been associated with proliferation in the human and mouse endometrium, we hypothesized that EGF, transforming growth factor-alpha (TGF alpha), and EGF receptor (EGF-R) expression in baboon endometrium may be modulated by the early invasive trophoblast and play a role in decidualization of the endometrial stroma.

METHODS

Endometrial tissue was obtained from cycling baboons (n = 4-5 per time point), ovariectomized steroid-treated baboons (n = 4 per group), or from pregnant baboons on days 18-60 of pregnancy (n = 2-4 per group). The tissue was fixed in Bouin's solution and embedded in paraffin for immunocytochemistry using polyclonal antibodies against EGF and EGF-R and a monoclonal antibody to TGF alpha.

RESULTS

Endometrial staining was located almost entirely in the glandular epithelium for TGF alpha and EGF-R in the follicular phase animals, whereas EGF staining was strongest in the periglandular stroma. In the luteal phase, specific staining for EGF also was detected in the glands as well as the periglandular stroma. There appeared to be little difference in endometrial staining between the late follicular and mid-luteal phase for TGF alpha and EGF-R. A similar pattern was observed in the steroid-treated animals. In the endometrium from pregnant animals, EGF, TGF alpha, and EGF-R intensely stained the glandular epithelium on days 18, 25, and 32. Both EGF and EGF-R showed light stromal staining on days 18 and 25. Light stromal TGF alpha staining was present on day 25 and became moderately intense by day 32. By day 60, the most intense staining for EGF and EGF-R was stromal. Staining of TGF alpha continued to be strong in the remaining epithelium through day 60. In placenta, EGF and EGF-R intensely stained the syncytiotrophoblast, but not the cytotrophoblast, whereas TGF alpha stained only the villous cytotrophoblast and intermediate cytotrophoblast within maternal blood vessels. There appeared to be no change in this staining pattern or intensity in the placenta throughout early pregnancy.

CONCLUSIONS

This study demonstrates the presence of EGF, TGF alpha, and EGF-R in the endometrium during the cycle and early pregnancy. The detection of EGF, TGF alpha, and EGF-R in the stromal cells during pregnancy correlated with the onset of decidualization. We propose that EGF, TGF alpha, and EGF-R may play a role in glandular development during the cycle and in decidualization and implantation during early pregnancy.

Epidermal growth factor, transforming growth factor-alpha, and epidermal growth factor receptor localization in the baboon (Papio anubis) oviduct during steroid treatment and the menstrual cycle

OBJECTIVES

Polypeptide growth factors may modulate the actions of estrogen (E2) and progesterone (P) in reproductive tissues in an autocrine/paracrine manner. The objective of this study was to determine whether the baboon oviduct contains epidermal growth factor (EGF), transforming growth factor-alpha (TGF alpha), and EGF receptor (EGF-R) and whether changes in their expression are correlated with various hormonal states.

METHODS

Oviductal tissue was obtained from adult female baboons (Papio anubis) after oophorectomy and steroid treatment, and during the menstrual cycle. Ampullary regions were fixed in Bouin's fixative and embedded in paraffin for immunocytochemistry using rabbit polyclonal antibodies against EGF and EGF-R, and mouse monoclonal antibody against TGF alpha.

RESULTS

Both EGF and EGF-R were present in all tissue compartments (most strongly in the epithelium, followed by smooth muscle and stroma) at all reproductive stages and showed similar staining patterns. However, the most intense immunoreactive product was found in the tissue obtained from the E2-treated and late follicular phase animals. At this time, intense staining was present in the apical regions of the mature ciliated cells, whereas the stain was dispersed uniformly over the cytoplasm of all other cell types. Immunoreactive TGF alpha was limited primarily to the nonciliated epithelial cells, and staining was most intense in the E2-treated and late follicular phase tissues. Transforming growth factor-alpha formed intense perinuclear deposits in the mature secretory cells, an area that corresponds to the Golgi region. No immunoreactive product was observed for any of these proteins when preimmune serum was substituted for the primary antibody or when the primary antibody was preabsorbed with antigen.

CONCLUSION

In summary, EGF, TGF alpha, and EGF-R are present in the ampulla of the baboon oviduct. Moreover, the localization and intensity of immunoreactive product are dependent on cell type and hormonal state. These data are consistent with the concept that EGF, TGF alpha, and EGF-R may be regulated by E2 and P and thus may play a role in cell differentiation and function. In addition, the specific localization of TGF alpha suggests that this growth factor may be synthesized for release from the secretory cells and thus may also function as a modulator of gamete/embryo viability and development.

Detection of insulin-like growth factor binding protein-1 in cat implantation sites

This study was undertaken to determine whether insulin-like growth factor binding protein-1 (IGFBP-1) was synthesized by the cat uterus and placenta during implantation and pregnancy. Endometrial and placental tissue explants from pregnant, pseudopregnant, and ovariectomized steroid-treated cats were cultured in the presence of 35S-methionine. Culture media proteins were separated by one-dimensional (1-D) and two-dimensional (2-D) SDS-PAGE, transferred to nitrocellulose, and immunostained using a rabbit polyclonal antibody against baboon IGFBP-1 and a murine monoclonal antibody to human IGFBP-1. The antibody cross-reacted with a protein with an M(r) = 30,000 and a pI = 5.1-5.4. Immunoreactive product was found in implantation site media from 16 days postcoitum (PC) through the end of pregnancy, and was confined to the superficial placental/junctional zone. Immunoreactivity was not detected in non-implantation site media until 7 wk PC and was never detected in serum or in media from liver, pseudopregnant endometrium, or endometrium from steroid-treated cats. Autoradiography and immunostaining of 2-D Western blots of culture media proteins demonstrated that implantation site and not non-implantation site tissue synthesized and released immunoreactive IGFBP-1 into the culture medium. 125Insulin-like growth factor-1 (IGF-1) specifically bound to this protein on 1-D Western ligand blots. Avidin-biotin immunocytochemistry utilizing the monoclonal antibody was used to localize IGFBP-1 in paraffin sections. Specific immunostaining was observed in the surface and glandular epithelium of the non-site endometrium throughout pregnancy, with stromal cell staining being detected later.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinol-binding protein in the baboon (Papio anubis) uterus: immunohistochemical characterization and gene expression

Retinols and retinoic acid (vitamin A) are essential for embryonic development; they are transported in circulation bound to retinol-binding protein (RBP). RBP has been shown to be synthesized in extrahepatic sites, i.e., the progestational uterus and concepti of pig, sheep, and cows. This study was undertaken to determine whether RBP is also synthesized by the primate reproductive tract. Uterine tissues were obtained from mature female baboons during the follicular and luteal stages of the menstrual cycle, after steroid (estrogen +/- progesterone) treatment of ovariectomized baboons and between Days 18 and 32 of pregnancy. Portions of the uterine tissues were either fixed in Bouin's fixative and embedded in paraffin, subjected to explant culture, or immediately frozen in liquid nitrogen for RNA isolation. Our studies indicate that RBP is present in the uterine glandular epithelium of the baboon during the late luteal stages of the menstrual cycle. Steroid hormone treatment of ovariectomized female baboons confirmed that both transcription and translation of uterine RBP is under progestational control. When uterine and placental tissues from pregnant baboons were analyzed between Days 18 and 32 of pregnancy, it was apparent that immunoreactive RBP increased in the mid and basal glands initially, but by Day 32 all of the glands stained positively. In contrast, the mRNA levels peaked at Day 25, and RBP message was more highly expressed in the basalis region of the uterus compared to the functionalis. Immunoreactivity for RBP was higher at the implantation site compared to the nonimplantation site. Neither RBP protein nor message was detectable in the baboon conceptus/placenta.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro incubation of golden (Syrian) hamster ovarian oocytes and human sperm with a human oviduct specific glycoprotein

The objective of this study was to determine if human oviduct specific glycoprotein (huOGP) would associate with hamster ovarian oocytes and human sperm during in vitro incubation. The huOGP used in these studies was partially purified from human hydrosalpinx fluid. Hamster ovarian oocytes and human sperm samples were incubated in culture medium with and without huOGP. Association of huOGP was assessed by indirect immunofluorescence assay using a polyclonal antibody prepared against huOGP. Intense fluorescence of the zona pellucida, and bright but uneven fluorescence of the perivitelline space, were observed in hamster ovarian oocytes following incubation in the presence of huOGP. A similar but more uniform pattern of fluorescence was observed when hamster oviductal oocytes (positive controls) were incubated in culture medium alone. Fluorescence was absent when oocytes were assayed with preimmune serum. The association of huOGP with the zona pellucida and perivitelline space appeared to be specific since thyroglobulin, a large molecular weight glycoprotein, and human serum albumin, the major protein in oviduct fluid, did not associate with the hamster oocytes nor inhibit huOGP association when included in the culture medium. Fluorescence was absent when human sperm incubated with huOGP were assayed with antiserum to huOGP. However, human sperm fluoresced when incubated with a uterine glycoprotein, CUPED, which had previously been shown to bind to cat sperm during in vitro incubation. Sperm also fluoresced brightly when human sperm antibody was used as a positive control. Solubilization of sperm membrane proteins postincubation and analysis of these proteins by 1-D SDS-PAGE followed by immunoblotting also failed to show an association of huOGP with human sperm. Electron microscopy of sperm both pre- and postsolubilization confirmed that the sperm membranes were removed by this process. In conclusion, the association of huOGP with hamster oocytes in vitro suggests that huOGP may associate with human oocytes in vivo, whereas that may not be true for human sperm in vivo. The association of huOGP with oocytes may serve to facilitate the process of fertilization and early embryonic development within the oviduct.

Characterization, localization, and regulation of receptors for insulin-like growth factor I in the baboon uterus during the cycle and pregnancy

The objective of this study was to determine the presence, regulation, and localization of specific receptors for insulin-like growth factor I (IGF-I) in primate reproductive tissues. Uteri were obtained from baboons either during the menstrual cycle, after ovariectomy with or without steroid treatments, or during early pregnancy (Days 18-60 postovulation [PO]). Placental and decidual tissues were collected from baboons during late pregnancy (Days 130-160). Localization of type I IGF receptor was determined by indirect immunocytochemistry (alpha IR3 antibody), and levels of type I IGF receptors were determined by affinity cross-linking and binding assays. Specific staining for type I IGF receptors was present in the membranes of glandular epithelial cells throughout the cycle and early pregnancy; however, there was a decrease in staining intensity by the late luteal phase and also throughout early pregnancy compared to the late follicular phase. Specific receptor staining was absent in stromal cells throughout the cycle. By Day 19 PO, stromal cells directly under the trophoblast were positive for type I IGF receptor, and an increase in stromal staining at the implantation site was observed as pregnancy proceeded. Stromal staining was apparent in non-implantation site tissue by Day 32 PO. Some placental villi showed positive receptor staining as early as on Day 18 PO, and an increase in the number of positive villi was apparent as pregnancy progressed. An 125I-IGF-I-protein complex of approximately 140,000 daltons, corresponding to the alpha subunit of the type I IGF receptor, was detected in endometrial, placental, and decidual membranes. The intensity of this signal was high in endometrium from the follicular phase, whereas low levels were detected in endometrium from the luteal phase. Throughout early pregnancy, alpha receptor subunit was present in placental and decidual membranes; alpha receptor subunit increased in placenta as pregnancy proceeded. An additional 125I-IGF-I-protein complex of 43,000 daltons, corresponding to IGF binding protein-1 (IGFBP-1), was present in decidual membranes and appeared to increase as pregnancy proceeded. Specific binding of 125I-IGF-I to placental membranes was displaced by unlabeled IGF-I and alpha IR3 antibody, whereas both unlabeled IGF-I and IGF-II competed equally for binding to decidual membranes. Scatchard analysis of 125I-IGF-I binding to placental membranes revealed a single class of high-affinity receptors (KD = 2.35 +/- 0.8 nM; mean +/- SEM).(ABSTRACT TRUNCATED AT 400 WORDS)

Secretory and morphological changes in the baboon (Papio anubis) uterus and placenta during early pregnancy

The study was undertaken to characterize changes in uterine endometrial secretory activity and morphology in the baboon between Days 18 and 32 of pregnancy. Proteins synthesized by the implantation site endometrium (RI) and non-implantation site endometrium (RIII) and developing placenta were analyzed by two-dimensional PAGE and fluorography. The electrophoretic mobility and localization of chorionic gonadotropin (CG) in the baboon placenta, and insulin-like growth factor binding protein-1 (IGFBP-1) and retinol binding protein (RBP) in the baboon uterus were confirmed by Western blot analysis and immunocytochemistry. Placental protein synthesis was primarily characterized by the presence of radiolabeled CG at Days 18 and 25, which decreased by Day 32. Peak CG synthetic activity, immunolocalized to the syncytiotrophoblast, occurred during the formation of tertiary villi. Also associated with the development of mature villi was a corresponding increase in a basic protein (M(r) 23,000). The overall secretory pattern of the baboon endometrium was similar to that observed during the midluteal stage; however, the synthetic activity was enhanced during pregnancy. Radiolabeled and immunoreactive IGFBP-1 and RBP were detectable in the Day 32 functionalis and basalis, respectively, and their synthesis was higher in RI compared to RIII. The immunolocalization of IGFBP-1 in RI appeared to be directly related to the degree of decidualization. In addition, a novel group of low molecular-weight (M(r) 27,000-30,000) isoelectrovariant proteins was secreted predominantly by the basalis at Days 18 and 25 of pregnancy and disappeared by Day 32 in all but one animal. The synthesis of this group of proteins did not show regional specificity. These studies indicate that the baboon endometrium undergoes morphological and secretory changes during pregnancy that are associated with the development of a functional placenta and decidualized endometrium. Furthermore, these studies suggest that the conceptus/placenta may mediate specific changes in IGFBP-1 and RBP expression at the implantation site.

Chorionic gonadotropin, estradiol, and progesterone levels in baboons (Papio anubis) during early pregnancy and spontaneous abortion

The purpose of this study was to sequentially characterize peripheral chorionic gonadotropin (CG), estradiol (E2), and progesterone (P) profiles during early pregnancy in the baboon (Papio anubis). Ten pregnant baboons were bled sequentially at eighteen time points between Days 8 and 128 of gestation. In addition, blood was obtained at corresponding time points from 5 spontaneously aborting baboons. CG levels were assessed in a mouse Leydig cell bioassay using rhesus pituitary LH as the standard E2 and P levels were measured by RIA. Pregnancy-associated CG activity was detectable by Day 15 (901.4 +/- 275.6 ng/ml), peaked at Day 27 (53,494.1 +/- 14,995.6 ng/ml), and then returned to baseline values by Day 51 (45.4 +/- 8.9 ng/ml). Mean E2 concentrations rose from 28.9 +/- 4.3 pg/ml on Day 8 to 280.6 +/- 145.5 pg/ml on Day 58 and then increased 9-fold to a level of 2436.4 +/- 928.0 pg/ml on Day 72. Mean E2 concentrations ranged between 2065.9 and 3830.9 pg/ml from Day 72 through Day 128. Mean P concentrations ranged from 7.5 to 10.2 ng/ml between Days 8 and 21, rising dramatically to 38.6 +/- 4.6 ng/ml on Day 37 prior to declining to levels that ranged from 11.1 to 17.1 ng/ml between Days 51 and 128. CG levels were low in 3 of 5 animals prior to spontaneous abortion E2 and P concentrations preceding spontaneous abortion were similar to values in uncomplicated pregnancy; however, at the time abortion was detected P concentrations in all 5 animals were 1.3 ng/ml or less.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological characterization and immunocytochemical localization of an oviduct-specific glycoprotein in the human

The objective of the current study was to generate a polyclonal antibody toward a previously described 110- to 130-kilodalton (kDa) human oviductal glycoprotein and to use the antibody to detect the protein in tissue sections, tissue culture media, and oviductal flushings. The polyclonal antibody was generated in male rabbits against the 110- to 130-kDa glycoprotein partially purified from hydrosalpinx fluid. Segments of human oviducts were either cut into 2- to 3-mm pieces and cultured for 24 h, or fixed and embedded in Araldite for light and electron microscopic immunocytochemistry. The protein was only present in midcycle oviductal flushings and was most evident in culture medium samples obtained at midcycle when analyzed on Western blots. No cross-reactivity was observed with proteins in human serum or human endometrial and cervical explant culture media. Immunoperoxidase staining was observed in the apical granules of the secretory cells lining the oviductal lumen. No staining was noted in other parts of the oviduct or in sections of human endometrium and cervix. Indirect immunogold localization demonstrated specific clustering of gold particles over the apical granules of the secretory cells. In summary, a polyclonal antibody to a 110- to 130-kDa human oviductal glycoprotein was successfully generated. This protein is found in the secretory cells and is released into the oviductal lumen. The synthesis of this protein appears to require elevated levels of estrogen and may play a role in early reproductive events occurring within the oviduct.

Insulin-like growth factor binding proteins in sera of pregnant nonhuman primates

Insulin-like growth factors (IGFs) are mitogenic peptides that are important for fetal and maternal tissue growth during pregnancy. They circulate complexed primarily with a serum binding protein, IGFBP-3, which regulates the availability of the IGFs to their target tissues. We previously reported that in pregnant women, serum IGFBP-3 levels, assessed by Western ligand blotting, decline markedly beginning at 6 weeks gestation due to a circulating protease that cleaves IGFBP-3 into a 29-kilodalton (kDa) protein and lower mol wt (M(r)) fragments. In the current study, we compared IGFBP profiles, IGFBP-3 and IGFBP-1 levels, and IGFBP protease activities in sera from pregnant and nonpregnant women, baboons, and rhesus monkeys, using Western ligand blotting, IGFBP-specific immunoassays, IGFBP-3 protease assay, and zymographic gel electrophoresis. Serum IGFBP profiles in nonpregnant human and nonhuman primates were similar and were not cycle-dependent. IGFBP-3 (37-43 kDa), IGFBP-2 (31 kDa), and IGFBP-1 (28 kDa) were identified in all three species using IGFBP-specific human antisera. A 24-kDa IGFBP was also present and is believed to be IGFBP-4. Serum IGFBP-1 levels increased throughout gestation in human and nonhuman primates. Serum IGFBP-2 and putative IGFBP-4 were barely detectable in all three species from midgestation to term, but increased several days postpartum. In contrast, serum IGFBP-3 profiles differed markedly between species during gestation. Rather than the decrease seen in human pregnancy serum, there was an increase in circulating IGFBP-3 levels in nonhuman primates. Furthermore, for both baboon and rhesus monkey, the M(r) of serum IGFBP-3 was about 2 kDa greater in pregnant than in nonpregnant animals, and deglycosylation studies suggested that the higher M(r) forms may be alternatively glycosylated or may have a unique primary structure. As in nonpregnant women, serum IGFBP-3 protease activity was absent in nonpregnant and pregnant baboons. However, rhesus monkey serum contained a calcium-dependent protease that cleaved recombinant human IGFBP-3 into unique fragments, compared to the human pregnancy enzyme. Unlike human pregnancy serum, which proteolyzes IGFBP-3, in human nonpregnancy serum, rhesus serum incubated under similar conditions did not result in proteolysis of rhesus IGFBP-3, suggesting that the IGFBP-3 protease in human pregnancy serum is not present in the circulation of the rhesus monkey. To assess proteolytic activity in these sera, zymographic polyacrylamide gel analysis, using gelatin as a substrate, was performed. A minor band of proteolytic activity (72 kDa) was observed in all three species throughout gestation.(ABSTRACT TRUNCATED AT 400 WORDS)