Steroid hormones acutely regulate expression of a Nudix protein-encoding gene in the endometrial epithelium of sheep

Steroid hormones regulate endometrial gene expression to meet the needs of developing embryos. Our hypothesis is that steroid hormones transiently induce expression of genes in the endometrial epithelium to make the uterine environment different between the earliest days of pregnancy. We identified one such gene product using differential display-polymerase chain reactions. The gene product that was strongly induced in ewes between day 3 and 6 of the estrous cycle was cloned and sequenced to identify it as encoding a member of the Nudix family of hydrolase enzymes. Northern blot analyses indicated that NUDT16 mRNA concentrations were elevated 10-fold in the endometrium of sheep from day 5 to 9 of the estrous cycle and returned to basal levels by day 11. In assays of RNA samples from 15 different tissues from an adult ewe, the concentrations of NUDT16 mRNA were greatest in endometrium. In situ hybridization localized NUDT16 mRNA exclusively to the endometrial epithelial cells of the glands and uterine lumen. In ovariectomized ewes, NUDT16 mRNA was induced by a regimen of alternating estrogen and progesterone therapy designed to mimic the hormonal experiences of a ewe at day 6 of the estrous cycle. The final estrogen treatment in the regimen was critical to the expression of NUDT16 as well as progesterone receptor and estrogen receptor-beta genes. Characterization of the NUDT16 gene identified putative steroid hormone response elements, which can now be investigated to understand its unique pattern of regulation in the earliest days of pregnancy.     

Estrogen regulates the expression of the small proline-rich 2 gene family in the mouse uterus

Small proline-rich (SPRR) proteins are structural components of the cornified cell envelope (CE), a specialized structure beneath the plasma membrane of stratified squamous epithelia. They are divided into four families, of which SPRR2 is the most complex consisting of 11 members (2a-2k) in the mouse. To assess the possible influence of estrogen on expression of the SPRR2 family in the uterus, we examined the effect of 17b-estradiol (E2) on SPRR2 mRNA levels on ovariectomized (OVX) adult mice. We employed a combination of laser capture microdissection (LCM) and semiquantitative RT-PCR to examine expression in particular uterine cell types - luminal epithelia, and stromal and muscle cells. We also used quantitative real-time PCR to measure levels of the mRNA of several SPRR2 proteins in the mouse uterus over the estrous cycle and during early pregnancy. Expression of SPRR2a, 2b, 2c, 2d, 2e, 2f and 2g mRNA was increased by estrogen treatment. SPRR2a, 2b, 2d and 2e were highly expressed on day 1 and 2 of pregnancy, but decreased markedly by days 3-6. Interestingly, several members of the SPRR2 family were preferentially up-regulated at implantation sites compared to inter-implantation sites around day 4 of pregnancy. They were abundant during proestrus and estrus but declined rapidly during metestrus. These results indicate that estrogen is a key regulator of the expression of the SPRR2 family in the mouse uterus during the estrous cycle and early pregnancy. In addition, they suggest that some members of the family play an important role in uterine processes such as the estrous cycle, early pregnancy and implantation.     

The effects of estrogen,its antagonist ICI 182, 780, and interferon-tau on the expression of estrogen receptors and integrin alphaV beta 3 on cycle day 16 in bovine endometrium

We have shown previously that downregulation of intercaruncular stromal integrin α_vβ₃ in bovine endometrium on day 16 of the estrous cycle coincided with the antibody recognition of estrogen receptors (ER) in the luminal epithelium. In pregnancy, these changes were not observed. Our hypothesis was that on day 16 of the estrous cycle, estrogen from the dominant follicle causes a reduction in integrin α_vβ₃ and affects ERα in the luminal epithelium. The pregnancy recognition protein, interferon-τ (IFN-τ), may prevent downregulation of integrin α_vβ₃ and suppress ERα expression in the luminal epithelium. On days 14 to 16, heifers received uterine infusions of the anti-estrogen ICI 182, 780, estradiol 17β, IFN-τ or the saline control. On day 16, reproductive tracts were collected for analysis of integrin α_vβ₃ and ERα. Estrogen receptor α immunoreactivity was largely restricted to the luminal epithelium in control animals. Using anti-ERα recognizing the amino terminus, estrogen-treated animals showed reactivity in the stroma, shallow and deep glands and myometrium as is typical of estrus, whereas ICI 182, 870 treated heifers showed little or no reactivity. In contrast, carboxyl terminus-directed antibodies showed a widespread distribution of ERα with reactivity detected in the uterine epithelium, stroma and myometrium of both estrogen and ICI 182, 780 treated animals. Heifers treated with IFN-τ had low ERα reactivity overall. Control and IFN-τ treated heifers had lower intercaruncular stromal expression of integrin α_vβ₃ in comparison to estrogen and ICI 182, 780 treatments. Overall, the results suggest that on day 16 of the estrous cycle, estrogen effects on integrin α_vβ₃ are indirect and do not directly involve ERα in the luminal epithelium. During pregnancy, interferon-tau may block ERα in the luminal epithelium but likely does not rescue integrin α_vβ₃ expression.     

Progesterone regulation of the mammalian ortholog of methylcitrate dehydratase (immune response gene 1) in the uterine epithelium during implantation through the protein kinase C pathway

Implantation requires coordination between development of the blastocyst and the sex steroid hormone-regulated differentiation of the uterus. Under the influence of these hormones, the uterine luminal epithelium becomes receptive to attachment of the hatched blastocyst. In this study we sought to identify genes regulated by progesterone (P4) in the uterine epithelium. This resulted in the identification of one novel P4-regulated gene that had been previously found in lipopolysaccharide-stimulated macrophages and called immune response gene-1 (Irg1) and which is the mammalian ortholog of the bacterial gene encoding methylcitrate dehydratase. In adult mice Irg1 expression was limited to the uterine luminal epithelium where it is expressed only during pregnancy with a peak coinciding with implantation. Irg1 mRNA expression is regulated synergistically by P4 and estradiol (E2) but not by E2 alone. In macrophages Irg1 is induced by lipopolysaccharide through a protein kinase C (PKC)-regulated pathway. Now we demonstrate that the PKC pathway is induced in the uterine epithelium at implantation by the synergistic action of P4 and E2 and is responsible for the hormone induction of Irg1. These results suggest that the PKC pathway plays an important role in modulating steroid hormone responsiveness in the uterine luminal epithelium during the implantation window and that Irg1 will be an important marker of this window and may play an important role in implantation.     

Induction of riboflavin-carrier protein in the immature male rat by estrogen: Kinetic and hormonal specificity

The kinetics of estrogen-induced accumulation of riboflavin-carrier protein in the plasma was investigated in immature male rats using a specific and sensitive homologous radio-immunoassay procedure developed for this purpose. Following a single injection of the steroid hormone, plasma riboflavin-carrier protein levels increased markedly after an initial lag period of approximately 24 h, reaching peak levels around 96 h and declining thereafter. A 1.5 fold amplification of the inductive response was evident on secondary stimulation with the hormone. The magnitude of the response was dependent on hormonal dose, whereas the initial lag phase and the time of peak riboflavin-carrier protein induction were unaltered within the range of the steroid doses (0.1–10 mg/ kg body wt.) tested. Simultaneous administration of progesterone did not affect either the kinetics or the maximum level of the protein induced. The hormonal specificity of this induction was further adduced by the effect of administration of antiestrogens viz., En and Zu chlomiphene citrates, which effectively curtailed hormonal induction of the protein. That the induction involvedde novo-protein synthesis was evident from the complete inhibition obtained upon administration of cycloheximide. Passive immunoneutralization of endogenous riboflavin-carrier protein with antiserum to the homologous protein terminated pregnancy in rats confirming the earlier results with antiserum to chicken riboflavin-carrier protein.     

Estrogen-induced synthesis of riboflavin-binding protein in immature chicks kinetics and hormonal specificity

The kinetics of estrogen-induced elevation in the plasma concentration of riboflavin-binding protein, a minor yolk constituent, was investigated in immature male chicks, using a specific and sensitive radioimmunoassay proceudre. Following a single injection of the hormone, the plasma riboflavin-binding protein content was enhanced several-fold at 6 h. reaching peak levels around 48 h and declining thereafter. A two-fold amplication of the response was evident on secondary stimulation with the hormone. A 4-h lag phase prior to onset of induction was noticed during both primary and secondary stimulat ions with the steroid hormone. The magnitude of the response was dependent on the hormonal dose whereas the initial lag phase and the time of peak riboflavin-binding protein accumulation were unaltered within the range of hormonal doses tested. The half-life of riboflavin-binding protein in the circulation was 10 h, as calculated from measurement of the rate of disappearance of exogenously administered ¹²⁵I-labelled protein. Simultaneous administration of progestrone did bot affect the kinetics of riboflavin-binding protein production. On the other hand, the antiestrogens, cis- and trans-clomiphene citrates, given 30 min prior to estrogen and cycloheximide, effectively countered the hormone-induced riboflavin-binding protein elaboration. Both progesterone and the anti-esterogens per se were completely ineffective in substituting for estrogen in the inductive ptrocess.     

Determination of progesterone and of free and conjugated estrogens in pregnant and pseudo-pregnant rats

Rat progesterone and estrogen levels have been determined in peripheral, ovarian, foetal plasma and in amniotic fluid, during estrous cycle, pseudo-pregnancy and pregnancy. From the progesterone levels, it was concluded that the predominant source of this hormone is the ovary. Though an ovarian contribution could not be excluded, placental origin of estrogens during pregnancy appeared evident. The estrogen levels showed the preponderance of the free form in a ratio E₂/E₁ < 1.     

Acute and chronic estrogen supplementation decreases uterine sympathetic innervation in ovariectomized adult virgin rats

Uterine innervation undergoes substantial reorganization associated with changes in reproductive status. Nerves innervating the uterus are decreased in pregnancy and puberty, and even the normal rodent estrous cycle is characterized by fluctuations in numbers of myometrial nerve fibers. During the follicular (proestrus/estrous) phase of the estrous cycle, intact nerves are rapidly depleted and then return over the next 2-3 days in the luteal (metestrus/diestrus) phase. We hypothesize that uterine nerve depletion is initiated by increased circulating estrogen in the follicular phase. However, studies have not shown whether estrogen can reduce uterine innervation and, if so, whether the time course is compatible with the rapid changes observed in the estrous cycle. These questions were addressed in the present study. Mature ovariectomized virgin rats received 17-beta-estradiol as a single injection (10 microg/kg s.c.) or chronically from timed-release pellets (0.1 microg/pellet for 3 weeks sustained release). Total (protein gene-product 9.5-immunoreactive) and sympathetic (dopamine beta-hydroxylase-immunoreactive) uterine innervation was assessed quantitatively. Both total and sympathetic innervation was abundant in uterine longitudinal smooth muscle of ovariectomized rats. However, following acute or chronic estrogen administration, total and sympathetic fiber numbers were markedly decreased. This was not due to altered uterine size, as reductions persisted after correcting for size differences. Our results indicate that sympathetic nerves are lost from uterine smooth muscle after estradiol treatment in a manner similar to that seen in the intact animal during estrus and pregnancy. This suggests that the rise in estradiol prior to estrus is sufficient to deplete uterine sympathetic innervation.     

Characterization and immunolocalization of bovine uterine retinol-binding protein.

Endometrial explants obtained from cows between Days 13 and 29 of pregnancy were cultured for 24 h in modified minimum essential medium in the presence of [35S]methionine or [3H]leucine. Proteins synthesized and released into medium were analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography. Uterine luminal flushings were obtained from cyclic cows (Days 2-20 of estrous cycle) and early pregnant cows (Days 17-22). Endometrial tissues from cows on Days 17 and 29 of pregnancy were prepared for immunocytochemistry. A uterine secretory protein, which consisted of five isoelectric variants (pI 5.3-6.1) of identical molecular mass (23,000 Da), was shown to react immunologically with antiserum raised against bovine placental retinol-binding protein (bpRBP). Limited N-terminal sequence analysis of two major isoforms showed that the protein had nearly complete homology with bovine placental and plasma retinol-binding protein (RBP) over the first 25 amino acids. Through use of bpRBP antiserum, immunoreactive RBP was detected in uterine flushings collected from cows in the late luteal phase of the estrous cycle and early pregnancy by Western blotting, and in medium conditioned by uterine explants prepared at Days 13-29 of pregnancy by immunoprecipitation. Immunoreactive RBP was localized in endometrial surface and glandular epithelium on Days 17 and 29 of pregnancy by immunocytochemistry. These results demonstrate that RBP is a product of bovine uterine tissues. The uterine RBP may play an important role in vitamin A transport between maternal tissues and developing embryos.     

Porcine endometrial expression of kininogen,factor XII,and plasma kallikrein in cyclic and pregnant gilts

Establishment of pregnancy in the pig is accompanied by a localized uterine acute inflammatory response and increase in uterine blood flow. Following rapid trophoblast elongation on Day 12 of pregnancy there is an increase in tissue kallikrein activity and release of bradykinin into the uterine lumen, suggesting the kallikrein-kininogen-kinin system is active in the porcine uterus. The present study investigated endometrial expression and presence of the various factors of the kallikrein-kininogen-kinin system. Endometrial L- and H-kininogen gene expression as well as presence of kininogens in the uterine flushings was evaluated throughout the estrous cycle and early pregnancy in the pig. The possible involvement of plasma kallikrein and Factor XII, activators of the kallikrein-kininogen-kinin system, were evaluated through analysis of gene expression in endometrial and conceptus tissues. Gene expression for plasma kallikrein, Factor XII, and H-kininogen were detected in endometrium but not early conceptus tissues. Factor XII and H-kininogen gene expression were similar across the days of the estrous cycle and early pregnancy. Endometrial plasma kallikrein gene expression was low but increased on Day 15 of the estrous cycle, whereas expression was similar across the days of early pregnancy. In comparison to cyclic gilts, endometrial L-kininogen gene expression increased fourfold on Days 15 and 18 of pregnancy. Both L- and H-kininogen were detected in the uterine flushings of cyclic and pregnant gilts. Presence of L- and H-kininogen in the porcine uterus and endometrial gene expression of plasma kallikrein and Factor XII provide evidence that the kallikrein-kininogen-kinin system is biologically active during establishment of pregnancy in the pig.     

Microfluorometric study of glucose-6-phosphate and malate dehydrogenases in histologically defined areas of the uterus in cyclic and pregnant ewes

Activities of glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49; G6PDH) and malate dehydrogenase (E.C. 1.1.1.37; MDH) were determined fluorometrically in freeze-dried sections of the sheep uterus during the estrous cycle and pregnancy. Samples (0.2–0.3 μg) from the luminal epithelium, uterine glands, maternal caruncles, fetal cotyledons and intercotyledonary trophoblast were assayed in a small aliquot (5 μl) of the reaction medium under oil.Activity of G6PDH in the luminal epithelium, uterine glands and maternal caruncles did not change during the estrous cycle. Activity of MDH in the uterine glands did not change during the cycle, but in the luminal epithelium and maternal caruncles highest activities were found on day 9 and day 2 post-estrus, respectively.The enzyme activities in the fetal tissues were lower than in the maternal tissues. In all maternal tissues, MDH and G6PDH activities decreased during early pregnancy, but after implantation, the activities increased significantly. In fetal tissues G6PDH activity increased, whereas MDH activity decreased during the second half of gestation. These results suggest an increased rate of pentose shunt activity in both maternal and fetal tissues, and an increased rate of Krebs' cycle activity in the maternal but not in the fetal tissues.     

The rat uterine oestrogen receptor in relation to intra-uterine devices and the oestrous cycle [proceedings

There are changes in the nuclear content of the estrogen receptor in the rat uterus during the estrous cycle that are associated with changes in its physiology. The changes correlate with the concentrations of circulating estradiol. It appears that uterotrophic response to estradiol is a function of the nuclear receptor. The insertion of an IUD leads to changes in the treated uterine horn which appear to be the result of an increased responsitivity to circulating estradiol. The presence of an IUD did not alter the estrous cycle, gonadotropin, or corpus luteum function. The intracellular distribution of the estrogen receptor was investigated in normal uterine horns and in the horns with devices throughout the estrous cycle. Groups of 30 Wistar rats had a silk suture fitted in the lumen of 1 uterine horn. After 14 days the progress of these estrous cycles was determined. Rats were grouped according to the stage of the cycle on the 4th day. Rats were then killed and the uteri removed. Cytosol receptors were measured. The capacity of the cytosol estrogen receptor to bind to oligo(dT)-cellulose was determined. Cytosol protein, nuclear protein, and DNA were measured. At all stages of the estrous cycle, the wet weight and cytosol receptor of the treated horns were greater than the control horns. A slight increase in the capacity of cytosol receptor to bind to oligo(dT)-cellulose was noted at proestrus. The response elicited by the IUD was not considered to be due to an estrogenic response since the changes observed were not accompanied by a corresponding increase in the content of nuclear receptor.     

Histamine content and mast cells distribution in mouse uterus: the effect of sexual hormones, gestation and labor

The histamine content of uteri from mice was analyzed in terms of both concentration and total amount per uterine horn a) at two stages of the estrous cycle (estrous and diestrous), b) under sex hormone treatment, c) during pregnancy and after delivery. Histamine concentration and mast cell density were greater during diestrous and in mice treated with progesterone (p less than 0.001). This effect was attributed to a reduction in uterine mass weight, since the amount of histamine per uterine horn remained constant throughout the estrous cycle. During pregnancy, both concentration and amount of histamine per uterine horn were increased, values were significantly higher than in estrous (p less than 0.001) from day 14-17 until day 21 when labor occurred. After six to eight hours post-partum an abrupt reduction on histamine content was observed. Mast cells were more abundant in myometrium than in endometrium, their density followed the same pattern as histamine concentration throughout the estrous cycle.     

Endocrine profiles during the estrous cycle and pregnancy in the Baird's tapir (Tapirus bairdii)

Serum samples were collected 1–3 times weekly from two Baird's tapirs (Tapirus bairdii) for 6 months in 1987–1988, and for more than 3 consecutive years beginning in 1989 to characterize hormone patterns during the estrous cycle and pregnancy. Based on serum progesterone concentrations, mean (±SEM) duration of the estrous cycle (n = 20) was 30.8 ± 2.6 days (range, 25–38 days) with a luteal phase length of 18.1 ± 0.4 days (range, 15–20 days). Mean peak serum progesterone concentrations during the luteal phase were 1.35 ± 0.16 ng/ml, and nadir concentrations were 0.19 ± 0.03 ng/ml during the interluteal period. Distinct surges of estradiol preceded luteal phase progesterone increases in most (14/20) cycles. Gestation length was 392 ± 4 days for three complete pregnancies. Mean serum progesterone concentrations increased throughout gestation and were 1.83 ± 0.13, 2.73 ± 0.13, and 4.30 ± 0.16 ng/ml during early, mid- and late gestation, respectively. Serum estradiol concentrations began to rise during mid-gestation, increasing dramatically during the last week of pregnancy. Patterns of serum estriol and estrone secretion during pregnancy were similar to that observed for estradiol. In contrast to progesterone and estrogens, serum cortisol concentrations were unchanged during pregnancy or parturition. Females resumed cycling 16.2 ± 2.0 days after parturition (n = 4) and, on two occasions, females became pregnant during the first postpartum estrus. These data suggest that the tapir cycles at approximately monthly intervals and that increases in serum progesterone are indicative of luteal activity. The interluteal period is relatively long, comprising approximately 40% of the estrous cycle. During gestation, progesterone concentrations are increased above luteal phase levels, and there is evidence of increased estrogen production during late gestation. The absence of increased cortisol secretion at the end of gestation suggests that this steroid does not play a major role in initiating parturition in this species. © 1994 Wiley-Liss, Inc.     

Changes in gonadotrophin and ovarian hormone levels during the estrous cycle of black-tailed deer (Odocoileus hemionus columbianus)

Daily blood samples over a fifteen day period were obtained from two adult female black-tailed deer and circulating levels of progesterone, estrogens, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were measured by radioimmunoassay. LH levels showed an apogee at the time when there was observed estrous behaviour. The length of the estrous cycle appeared to be 7 days. Progesterone levels peaked just subsequent to the LH peak. High estrogen levels coincided with high progesterone and prolactin levels. FSH reached maximum levels prior to peak estrogen levels. LH and FSH levels reached maxima on different days. There were two steroid peaks between the LH apogees.