Plasma membrane transformation: a common response of uterine epithelial cells during the peri-implantation period

Porosomes in uterine epithelial cells: Ultrastructural identification and characterization during early pregnancy

Porosomes are plasma membrane structures in secretory cells that allow transient docking and/or partial fusion of vesicles during which they release their content then disengage. This is referred to as "kiss and run" exocytosis. During early pregnancy, at the time of receptivity, there is a high level of vesicle activity in uterine epithelial cells (UECs). One of the secretory pathways for these vesicles could be via porosomes, which have yet to be identified in UECs. This study identified porosomes in the apical plasma membrane of UECs for the first time. These structures were present on days 1, 5.5, and 6 of early pregnancy, where they likely facilitate partial secretion via "kiss and run" exocytosis. The porosomes were measured and quantified on days 1, 5.5, and 6, which showed there are significantly more porosomes on day 5.5 (receptive) compared to day 1 (nonreceptive) of pregnancy. This increase in porosome numbers may reflect major morphological and molecular changes in the apical plasma membrane at this time such as increased cholesterol and soluble NSF attachment protein receptor proteins, as these are structural and functional components of the porosome complex assembly. Porosomes were observed in both resting (inactive) and dilated (active) states on days 1, 5.5, and 6 of early pregnancy. Porosomes on day 5.5 are significantly more active than on day 1 as demonstrated by the dilation of their base diameter. Further two-way ANOVA analysis of base diameter in resting and dilated states found a significant increase in porosome activity in day 5.5 compared to day 1. This study therefore indicates an increase in the number and activity of porosomes at the time of uterine receptivity in the rat, revealing a mechanism by which the UECs modify the uterine luminal environment at this time.

BMP/SMAD1/5 Signaling in the Endometrial Epithelium Is Essential for Receptivity and Early Pregnancy

The biological processes that control endometrial receptivity and embryo implantation are critical for the successful outcome of pregnancy. The endometrium is the complex inner lining of the uterine wall that is under the cyclical control of estrogen and progesterone and is a site of intimate contact between mother and blastocyst. The bone morphogenetic signaling (BMP) pathway is a highly conserved signaling pathway that controls key cellular processes throughout pregnancy and exerts intracellular effects via the SMAD1/5 transcription factors. To delineate the endometrial compartment-specific roles of BMP signaling, we generated mice with epithelial-specific conditional deletion of SMAD1/5 using Lactoferrin-icre (Smad1flox/flox;Smad5flox/flox;Lactoferrin-cre, "Smad1/5 cKO"). Histological analysis of the reproductive tracts showed that Smad1/5 cKO mice were developmentally normal and displayed no defects in glandular morphology. In fertility analyses, single SMAD1 or SMAD5 deletion had no effect on fertility; however, double-conditional deletion of SMAD1 and SMAD5 resulted in severe subfertility. Timed mating analyses revealed endometrial receptivity defects in the Smad1/5 cKO mice beginning at 3.5 days post coitum (dpc) that perturbed embryo implantation at 4.5 dpc, as demonstrated by the detection of unattached blastocysts in the uterus, decreased COX2 expression, and FOXO1 cytoplasmic mislocalization. We also found that defects that arose during peri-implantation adversely affected embryonic and decidual development at 5.5 and 6.5 dpc. Thus, uterine epithelial BMP/SMAD1/5 signaling is essential during early pregnancy and SMAD1/5 epithelial-specific deletion has detrimental effects on stromal cell decidualization and pregnancy development.

Hashimoto's thyroiditis impairs embryo implantation by compromising endometrial morphology and receptivity markers in euthyroid mice

BACKGROUND

Although thyroid dysfunction caused by Hashimoto's thyroiditis (HT) is believed to be related to implantation failure due to the underdevelopment of the receptive uterus, it is unknown whether HT itself, even in the euthyroid state, impairs embryo implantation associated with endometrial receptivity defects. To address whether HT itself can affect endometrial receptivity accompanied by implantation alterations, a euthyroid HT model was established in mice.

METHODS

Female NOD mice were immunized twice with thyroglobulin and adjuvant to induce the experimental HT model. Four weeks after the second treatment, the mice were normally mated, and pregnant ones were sacrificed in implantation window for thyroid-related parameter and steroid hormones measurements by electrochemiluminescence immunoassay and enzyme-linked immunosorbent assay and implantation site number calculation by uptake of Chicago Blue dye. In addition, certain morphological features of endometrial receptivity were observed by hematoxylin-eosin staining and scanning electron microscopy, and the expression of other receptivity markers were analyzed by immunohistochemistry, RT-qPCR or Western Blot.

RESULTS

HT mice displayed intrathyroidal monocyte infiltration and elevated serum thyroid autoantibody levels without thyroid dysfunction, defined as euthyroid HT in humans. Euthyroid HT resulted in implantation failure, fewer pinopodes, retarded pinopode maturation, and inhibited expression of receptivity markers: estrogen receptor α (ERα), integrin β3, leukemia inhibitory factor (LIF), and cell adhesion molecule-1 (ICAM-1). Interestingly, despite this compromised endometrial receptivity response, no statistical differences in serum estradiol or progesterone level between groups were found.

CONCLUSIONS

These findings are the first to indicate that HT induces a nonreceptive endometrial milieu in the euthyroid state, which may underlie the detrimental effects of HT itself on embryo implantation.

Diabetes mellitus increased integrins gene expression in rat endometrium at the time of embryo implantation

Background

Diabetes mellitus deeply changes the genes expression of integrin (Itg) subunits in several cells and tissues such as monocytes, arterial endothelium, kidney glomerular cells, retina. Furthermore, hyperglycemia could impress and reduce the rate of successful assisted as well as non-assisted pregnancy. Endometrium undergoes thorough changes in normal menstrual cycle and the question is: What happens in the endometrium under diabetic condition?

Objective

The aim of the current study was to investigate the endometrial gene expression of α3, α4, αv, Itg β1 and β3 subunits in diabetic rat models at the time of embryo implantation.

Materials and Methods

Twenty-eight rats were randomly divided into 4 groups: control group, diabetic group, pioglitazone-treated group, and metformin-treated group. Real-time PCR was performed to determine changes in the expression of Itg α3, α4, αv, β1, and β3 genes in rat's endometrium.

Results

The expression of all Itg subunits increased significantly in diabetic rats' endometrium compared with control group. Treatment with pioglitazone significantly reduced the level of Itg subunits gene expression compared with diabetic rats. While metformin had a different effect on α3 and α4 and elevated these two subunits gene expression.

Conclusion

Diabetes mellitus significantly increased the expression of studied Itg subunits, therefore untreated diabetes could be potentially assumed as one of the preliminary elements in embryo implantation failure.

Microtubules are reorganised and fragmented for uterine receptivity

For the development of uterine receptivity, many morphological and molecular changes occur in the apical surface of luminal uterine epithelial cells (UECs) including an increase in vesicular activity. Vesicular movements for exocytosis and endocytosis are dependent on microtubules; however, changes in microtubules in UECs during early pregnancy have received little attention. β-tubulin, one of the main component of microtubules, is distributed throughout the cytoplasm of UECs on day 1 (non-receptive) of pregnancy in the rat. On day 5.5, β-tubulin is concentrated above the nuclei and by day 6 (receptive), β-tubulin is concentrated in a band-like fashion above the nucleus. Western blot analysis of isolated UECs found two bands (50 and 34 kDa) for β-tubulin in UECs during early pregnancy. The intensity of the 34 kDa band was significantly higher on day 6 compared to day 1. The increase in the 34 kDa band may be due to higher proteolytic activity associated with microtubule polymerisation during the receptive state. Transmission electron microscopy showed fragmented microtubules at the time of receptivity in UECs. This is the first study to show that microtubules are reorganised during uterine receptivity. This re-organisation likely facilitates vesicular movement and promotes the reorganisation of the apical plasma membrane for uterine receptivity.

Prominin-1 glycosylation changes throughout early pregnancy in uterine epithelial cells under the influence of maternal ovarian hormones

In preparation for uterine receptivity, the uterine epithelial cells (UECs) exhibit a loss of microvilli and glycocalyx and a restructuring of the actin cytoskeleton. The prominin-1 protein contains large, heavily glycosylated extracellular loops and is usually restricted to apical plasma membrane (APM) protrusions. The present study examined rat UECs during early pregnancy using immunofluorescence, western blotting and deglycosylation analyses. Ovariectomised rats were injected with oestrogen and progesterone to examine how these hormones affect prominin-1. At the time of fertilisation, prominin-1 was located diffusely in the apical domain of UECs and 147- and 120-kDa glycoforms of prominin-1 were identified, along with the 97-kDa core protein. At the time of implantation, prominin-1 concentrates towards the APM and densitometry revealed that the 120-kDa glycoform decreased (P<0.05), but there was an increase in the 97-kDa core protein (P<0.05). Progesterone treatment of ovariectomised rats resulted in prominin-1 becoming concentrated towards the APM. The 120-kDa glycoform was increased after oestrogen treatment (P<0.0001), whereas the 97-kDa core protein was increased after progesterone treatment (P<0.05). Endoglycosidase H analysis demonstrated that the 120-kDa glycoform is in the endoplasmic reticulum, undergoing protein synthesis. These results indicate that oestrogen stimulates prominin-1 production, whereas progesterone stimulates the deglycosylation and concentration of prominin-1 to the apical region of the UECs. This likely presents the deglycosylated extracellular loops of prominin-1 to the extracellular space, where they may interact with the implanting blastocyst.

Uterine RAC1 via Pak1-ERM signaling directs normal luminal epithelial integrity conducive to on-time embryo implantation in mice

Successful embryo implantation requires functional luminal epithelia to establish uterine receptivity and blastocyst-uterine adhesion. During the configuration of uterine receptivity from prereceptive phase, the luminal epithelium undergoes dynamic membrane reorganization and depolarization. This timely regulated epithelial membrane maturation and precisely maintained epithelial integrity are critical for embryo implantation in both humans and mice. However, it remained largely unexplored with respect to potential signaling cascades governing this functional epithelial transformation prior to implantation. Using multiple genetic and cellular approaches combined with uterine conditional Rac1 deletion mouse model, we demonstrated herein that Rac1, a small GTPase, is spatiotemporally expressed in the periimplantation uterus, and uterine depletion of Rac1 induces premature decrease of epithelial apical-basal polarity and defective junction remodeling, leading to disrupted uterine receptivity and implantation failure. Further investigations identified Pak1-ERM as a downstream signaling cascade upon Rac1 activation in the luminal epithelium necessary for uterine receptivity. In addition, we also demonstrated that Rac1 via P38 MAPK signaling ensures timely epithelial apoptotic death at postimplantation. Besides uncovering a potentially important molecule machinery governing uterine luminal integrity for embryo implantation, our finding has high clinical relevance, because Rac1 is essential for normal endometrial functions in women.

Anastrozole is a dose-specific superovulator and favors implantation in rats: a prospective study

An alternative superovulator to replace clomiphene citrate (CC) is needed as it is unsuitable for women with polycystic ovarian syndrome and is associated with low pregnancy rates. Anastrozole is an effective superovulator, but has not been well researched. The aim of this study was to determine the optimal dose of anastrozole as a superovulator and ascertain its effects on implantation and uterine ultrastructure during early pregnancy in Wistar rats using scanning electron microscopy. The uterine morphological characteristics which were studied in day 1 and 6 pregnant rats include microvilli density, length, surface "beads", surface glycocalyx, cell borders and apices, uterine surface fording and large surface protrusions. A significant increase in implantation sites is seen in the 15 mg/kg anastrozole group, compared to control. Day 1 and 6 anastrozole groups have similar morphology to the control and different to the CC group. At day 6, large surface protrusions are mostly noted but not limited to anastrozole-treated rats; anastrozole also appears to retain glycocalyx to some extent. The increased number of implantation sites in the 15 mg/kg anastrozole group suggests that this dose superovulates and favors implantation. Anastrozole is probably dose-/species-specific and additionally the surface uterine morphology suggests that anastrozole is implantation friendly.

Insights into the paracrine effects of uterine natural killer cells

Uterine natural killer (uNK) cells are recruited into the uterus during establishment of the implantation and placentation of the embryo, and are hypothesized to regulate uterine spiral artery remodeling and angiogenesis during the initial stages of pregnancy. Failures in uNK cell activation are linked to diseases associated with pregnancy. However, the manner in which these cells interact with the endometrium remain unknown. Therefore, this study investigated the paracrine effects of uNK cells on the gene expression profile of an endometrial epithelial and stromal cell co‑culture system in vitro, using a microarray analysis. Results from reverse transcription‑quantitative polymerase chain reaction and enzyme‑linked immunosorbent assay experiments showed that soluble factors from uNK cells significantly alter endometrial gene expression. In conclusion, this study suggests that paracrine effects of uNK cells guide uNK cell proliferation, trophoblast migration, endometrial decidualization and angiogenesis, and maintain non‑cytotoxicity of uNK cells.

Ion/Water Channels for Embryo Implantation Barrier

Successful implantation involves three distinct processes, namely the embryo apposition, attachment, and penetration through the luminal epithelium of the endometrium to establish a vascular link to the mother. After penetration, stromal cells underlying the epithelium differentiate and surround the embryo to form the embryo implantation barrier, which blocks the passage of harmful substances to the embryo. Many ion/water channel proteins were found to be involved in the process of embryo implantation. First, ion/water channel proteins play their classical role in establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane. Second, most of ion/water channel proteins are regulated by steroid hormone (estrogen or progesterone), which may have important implications to the embryo implantation. Last but not least, these proteins do not limit themselves as pure channels but also function as an initiator of a series of consequences once activated by their ligand/stimulator. Herein, we discuss these new insights in recent years about the contribution of ion/water channels to the embryo implantation barrier construction during early pregnancy.

Mucin 15 is lost but mucin 13 remains in uterine luminal epithelial cells and the blastocyst at the time of implantation in the rat

The glycocalyx of the uterine luminal epithelium in the rat undergoes considerable reduction before implantation. In particular, the reduction of some mucins is necessary to facilitate blastocyst adhesion and subsequent implantation. The present study investigated the localisation, abundance and hormonal control of two mucin proteins, Muc13 and Muc15, in rat uterine epithelial cells during early pregnancy to determine whether they are likely to play a role in uterine receptivity for implantation. Muc13 and Muc15 are localised to the uterine luminal epithelium but show a presence and an absence, respectively, at the apical cell surface at the time of implantation. This localisation corresponds to changes in the molecular weights of Muc13 and Muc15, as shown with western blotting analysis. Furthermore, the localisation of Muc13 and Muc15 was shown to be controlled by the ovarian hormones, oestrogen and progesterone, and they were also localised in preimplantation rat blastocysts. Our results suggest that Muc15 may operate in an anti-adhesive capacity to prevent implantation while Muc13 potentially functions in either an adhesive or cell-signalling role in the events of implantation.

Temporal and spatial regulation of ezrin-radixin-moesin-binding phosphoprotein-50-kDa (EBP50) during embryo implantation in mouse uterus

Embryo implantation is a crucial process for successful pregnancy. To date, the mechanism of embryo implantation remains unclear. Ezrin-radixin-moesin-binding protein-50-kDa (EBP50) is a scaffold protein, which has been shown to play an important role in cancer development. Embryo implantation and cancer follow a similar progression. Thus, in this article, we utilized immunohistochemical staining and western blot analyses to examine the spatiotemporal expression and regulation of EBP50 both in the mouse uterus during embryo implantation as well as in other related models. We found that EBP50 was detected in epithelial cells in all of the groups used in our study. During the peri-implantation period, EBP50 mainly localized in apical membranes. At the implantation site (IS) on day 5 (D5) of pregnancy, EBP50 was mainly expressed in the nuclei of stroma cells, whereas from day 6 to day 8 (D6&#8211;D8) of pregnancy, the expression of EBP50 was noted in the cytoplasm of decidual cells. The expression of EBP50 was not significantly different in the pseudopregnant uterus and decreased in the uteri subjected to activation of delayed implantation. Artificial decidualization also decreased EBP50 expression. Thus, the expression levels and location were affected by active blastocysts and decidualization during the window of implantation.

Endometrial receptivity defects and impaired implantation in diabetic NOD mice

Implantation failure is a major hurdle to a successful pregnancy. The high rate of postimplantation fetal loss in nonobese diabetic (NOD) mice is believed to be related to an abnormal decidual production of interferon (IFN)gamma. To address whether diabetes alters the natural events associated with successful implantation, certain morphological and molecular features of uterine receptivity in diabetic NOD (dNOD) mice were examined in normally mated pregnancy and in concanavalin A (ConA)-induced pseudopregnancy. As opposed to normoglycemic NOD (cNOD) mice, dNOD mice expressed retarded maturation of their uterine pinopodes and overexpressed MUC1 mucin at implantation sites (P < 0.001). Uterine production of leukemia inhibitory factor (LIF) and phosphorylation of uterine NFkappaBp65 and STAT3-Ty705 were found to be low (P < 0.01) during Day 4.5 postcoitum, whereas IFNgamma was aberrantly overexpressed. Loss of temporal regulation of progesterone receptor A (PR A) and PR B, together with aberrantly increased expression of the protein inhibitor of activated STAT-y (PIASy) (P < 0.01) and reduced recruitment (P < 0.01) of the latter to nuclear progesterone receptor sites were prominent features of decidualization failure occurring at peri-implantation in dNOD mice. In conclusion, the aberrant expression of endometrial IFNgamma in dNOD mice is associated with a nonreceptive endometrial milieu contributing to peri-implantation embryo loss in type 1 diabetes.

Ovarian hormones control the changing expression of claudins and occludin in rat uterine epithelial cells during early pregnancy

Regulation of the uterine luminal environment is important for successful attachment and implantation of the blastocyst. The contents and volume of luminal fluid are regulated in part by the tight junctions. Using immunofluorescence microscopy, protein and RNA analysis, the cellular distributions of tight junction components claudins and occludin were observed during early pregnancy and under various hormonal regimens. Results indicate that occludin and claudin-4 distribution changed during early pregnancy and in response to ovarian hormones. At the time of implantation and in response to progesterone administration to ovariectomised rats, occludin and claudin-4 showed increased immunolabelling in luminal epithelium. Interestingly, occludin protein detection in uterine luminal epithelial cells at the time of implantation was statistically significantly decreased at the time of implantation compared to day 1 of pregnancy. This suggests that a cytoplasmic pool of occludin is present at day 1 of pregnancy and is redistributed to the tight junctions at the time of implantation. The presence of occludin and claudin-4 in the tight junctions at the time of implantation and in response to progesterone suggests that the paracellular pathway is impermeable to water and Na(+) at this time, and that the transport of such substances takes place via the transcellular pathway.

Focal adhesions disassemble during early pregnancy in rat uterine epithelial cells

During early pregnancy in rodents, invasion of the blastocyst into the endometrial decidual cells is accompanied by the removal of uterine epithelial cells around the implantation sites. The present study investigated the distribution and expression of two focal adhesion proteins, namely talin and paxillin, in rat uterine epithelial cells during early pregnancy and their role in the loss of these cells at the time of implantation. A major distributional change of talin and paxillin was demonstrated in uterine epithelial cells during early pregnancy. From a highly concentrated expression along the basal cell surface on Day 1 of pregnancy, talin and paxillin were lost from the basal cell surface at the time of implantation. There was also a corresponding statistically significant decrease in paxillin seen through western blotting analysis. Together, these observations suggest that uterine epithelial cells are less adherent to the underlying basal lamina due to the disassembly of talin and paxillin from focal adhesions, facilitating removal of these cells at the time of implantation. This phenomenon was restricted to the period of receptivity because talin and paxillin reappeared along the basal cell surface soon after implantation.

Expression and localization of galectin-9 in the human uterodome

Galectin-9 has been recently considered as a novel marker for the mid- and late-secretory phases of human endometrium and decidua. The aim of this study was to investigate the subcellular distribution of galectin-9 in the endometrial epithelium, especially during the frame of the implantation window. Endometrial biopsies in the proliferative, early, and mid-secretory phases from women with regular menstrual cycle were studied using several approaches, including scanning electron microscopy, immunostaining for light and transmission electron microscopies (TEM), immunoblotting, and statistical analysis of the area-related numerical densities of galectin-9-bound nanogold. Images of immunostaining for light microscopy demonstrated a strong expression of galectin-9 at the luminal and glandular endometrial epithelium in the mid-secretory phase compared to the proliferative and early secretory phases. Data of immunoblotting revealed a molecular weight of 36 kDa band with high intensity in the mid-secretory samples. Photomicrographs of immunogold staining for TEM illustrated the localization of galectin-9 in the uterodomes. Statistical and morphometric analysis showed a significantly higher area-related numerical density of galectin-9-bound nano-golds in the uterodomes compared to that of the uterodome-free areas of the luminal epithelium (p<0.001). This is the first demonstration of the molecular localization of galectin-9 in the bulbous ultrastructure of the human endometrial epithelium, called uterodomes. High expression of galectin-9 at uterodomes during the frame of implantation window suggests that galectin-9 can be considered as a marker of endometrial receptivity and should play an important role during the initial events of human embryo implantation.

Actin binding protein expression is altered in uterine luminal epithelium by clomiphene citrate, a synthetic estrogen receptor modulator

Clomiphene citrate (CC), a synthetic oestrogen, is often prescribed as a superovulator in treating infertility. Although CC works efficiently, pregnancy rates following CC treatment are approximately 10 times lower than "natural" rates. This study investigates how a dose of 1.25 mg CC given to ovariectomized rats before the implantation priming hormones (a single dose of progesterone for 3 days and a dose of estradiol-17beta on d3, P-P-PE), alters the expression and distribution of alpha-actinin, gelsolin and vinculin. Actin binding proteins show a specific distribution within the uterine epithelium during implantation, linking the actin cytoskeleton to integrin expression on the uterine surface and in this way aiding "adhesiveness" for blastocyst apposition to the uterine epithelium. In this study, immunocytochemistry on frozen uterine sections using mouse monoclonal antibodies against alpha-actinin, gelsolin and vinculin and peroxidase-conjugated secondary antibodies, show that CC, administered before the P-P-PE regimen, down-regulates the expression of vinculin, does not alter the expression of gelsolin and up-regulates alpha-actinin on the uterine apical surface, when compared to P-P-PE treated animals. All three proteins are down-regulated on the apical surface of the luminal epithelium and glands in all groups when compared to pregnant controls. Vinculin was only localized in the basolateral compartment of the uterine epithelial cells in the CC treated groups. By down-regulating these proteins on the uterine surface and up-regulating vinculin on the basolateral membrane of the epithelium, CC may impede adhesion and invasion of blastocysts at implantation. These results may aid the exogenous manipulation of uterine tissue to control fertility and improve assisted reproductive out-comes.

Apoptosis is not altered by clomiphene citrate in pseudopregnant rat uteri

Clomiphene citrate (CC) remains one of the most often prescribed synthetic oestrogens used in the treatment of infertility even though the ensuing pregnancy rates are low. CC alters the uterine environment on most levels. Ovariectomised rats were treated with 5 mg progesterone (P) for 3 days and a 0.5 microg injection of oestrogen (E) on the third day (PP(PE)) thus inducing pseudopregnancy and rendering the uterus receptive to implantation 24 h later. Using this model, we investigated apoptosis in the rat uterus treated with 0.25 mg CC given prior to the PP(PE) treatment. Apoptotic cells in the uterus were localised using TUNEL and visualised with a FITC marker. There was a similar increase in apoptosis in the uterine luminal epithelium in the PP(PE) and CCPP(PE) treated animals; no changes were observed in apoptosis in the other uterine compartments when compared to the control. The CCPP(PE)-treated tissue showed tall epithelial cells with long microvilli while the PP(PE) tissue had short microvilli and low cuboidal epithelium. These results suggest that CC does not disrupt the normal apoptotic activity seen at implantation, but does change the morphology of the luminal epithelium, suggesting that these cellular changes could influence successful implantation.

Demonstration of ubiquitin thiolester formation of UBE2Q2 (UBCi), a novel ubiquitin-conjugating enzyme with implantation site-specific expression

We recently identified a differentially expressed gene in implantation stage rabbit endometrium encoding a new member of the ubiquitin-conjugating enzyme family designated UBE2Q2 (also known as UBCi). Its unusually high molecular mass, novel N-terminus extension, and highly selective pattern of mRNA expression suggest a specific function in implantation. This study analyzes its relationship to the E2 ubiquitin-conjugating enzyme superfamily, investigates its enzymatic activity, and examines its localization in implantation site endometrium. Construction of a dendrogram indicated that UBE2Q2 is homologous to the UBC2 family of enzymes, and isoforms are present in a broad range of species. In vitro enzymatic assays of ubiquitin thiolester formation demonstrated that UBE2Q2 is a functional ubiquitin-conjugating enzyme. The Km for transfer of ubiquitin thiolester from E1 to UBE2Q2 is 817 nM compared to 100 nM for other E2 paralogs; this suggests that the unique amino terminal domain of UBE2Q2 confers specific functional differences. Affinity-purified antibodies prepared with purified recombinant UBE2Q2 showed that the protein was undetectable by immunoblot analysis in endometrial lysates from estrous and Day 6(3/4) pregnant (blastocyst attachment stage) rabbits but was expressed in both mesometrial and antimesometrial implantation site endometrium of Day 8 pregnant animals. No expression was detected in adjacent interimplantion sites. Immunohistochemistry demonstrated UBE2Q2 expression exclusively in mesometrial and antimesometrial endometrial luminal epithelial cells of the Day 8 implantation chamber. Immunohistochemical localization of ubiquitin mirrored UBE2Q2 expression, with low-to-undetectable levels in implantation sites of Day 6(3/4) pregnant endometrium but high levels in luminal epithelial cells of Day 8 pregnant endometrium. This implantation site-specific expression of UBE2Q2 in luminal epithelial cells could play major roles in orchestrating differentiation events through the modification of specific protein substrates.

Endometrial receptivity: Clinical assessment in relation to fertility, infertility, and antifertility

Fertility in humans and other mammalian species depends absolutely on synchronous events that render the developing blastocyst and the receiving uterus competent for implantation. Endometrial receptivity is defined as the period during which the endometrial epithelium acquires functional, but transient, ovarian steroid-dependent status supportive to blastocyst acceptance and implantation. Once inside the uterus, the blastocyst is surrounded by an intact luminal epithelium, which is considered to act as barrier to its attachment, except for this short period of high endometrial receptivity to blastocyst signal(s). Its transport and permeability properties, in conjunction with cellular action of the endometrium and the embryo, have been suggested to influence creation and maintenance of informational and nutritional status of uterine luminal milieu. This period, also termed as the 'window of implantation,' is limited to days 20-24 of menstrual cycle in humans. However, establishment of endometrial receptivity is still a biological mystery that remains unsolved despite marked advances in our understanding of endometrial physiology following extensive research associated with its development and function. This review deals with various structural, biochemical, and molecular events in the endometrium coordinated within the implantation window that constitute essential elements in the repertoire that signifies endometrial receptivity and is aimed to achieve a better understanding of its relationship to fertility, infertility, and for the development of targeted antifertility agents for human use and welfare.

Secretory role for human uterodomes (pinopods): secretion of LIF

The differentiation of human endometrial epithelium is a dynamic event, which occurs throughout the menstrual cycle in preparation for pregnancy. The appearance of uterodomes (pinopods) in this regard was first introduced in rodents with an established pinocytotic function, whereas little evidence was available in humans in this context. This study was undertaken to identify the potential physiological roles of uterodomes in the implantation process. To address this, endometrial biopsies from early, mid- and late luteal phases of the menstrual cycle of 23 fertile female patients with regular menses were used. Scanning and transmission electron microscopies (SEM and TEM) as well as immunofluorescence and immunogold TEM were performed to study the morphological changes and the expression pattern of leukaemia inhibitory factor (LIF) at uterodomes. Our results illustrated a high level of LIF expression in the human uterodomes, which was colocalized with the well-known biochemical markers of exocytosis, including syntaxin-1, 25-kDa synaptosomal protein (SNAP-25) and vesicle-associated membrane protein-2 (VAMP-2). Our morphological and immunocytochemical findings illustrated a secretory function for human uterodomes for the first time. In conclusion, this novel function for uterodomes provides an important clue in detection of their physiological function(s) during the process of the plasma membrane transformation.

Uterine receptivity and the plasma membrane transformation

This review begins with a brief commentary on the diversity of placentation mechanisms, and then goes on to examine the extensive alterations which occur in the plasma membrane of uterine epithelial cells during early pregnancy across species. Ultrastructural, biochemical and more general morphological data reveal that strikingly common phenomena occur in this plasma membrane during early pregnancy despite the diversity of placental types--from epitheliochorial to hemochorial, which ultimately form in different species. To encapsulate the concept that common morphological and molecular alterations occur across species, that they are found basolaterally as well as apically, and that moreover they are an ongoing process during much of early pregnancy, not just an event at the time attachment, the term 'plasma membrane transformation' is suggested which also emphasises that alterations in this plasma membrane during early pregnancy are key to uterine receptivity.

Progesterone treatment and the progress of early pregnancy reduce desmoglein 1&2 staining along the lateral plasma membrane in rat uterine epithelial cells

Uterine epithelium undergoes dramatic changes during early pregnancy in preparation for implantation. We have studied distribution patterns of the desmosomal marker, desmoglein 1&2, in rat uterine epithelial cells during early pregnancy as well as in hormonally stimulated ovariectomised animals. On day 1 of pregnancy as well as in oestradiol treated rats, desmoglein 1&2 staining was localized along the entire length of the lateral plasma membrane. By day 3 and on subsequent days of pregnancy as well as in ovariectomised animals treated with progesterone alone or in combination with oestradiol, desmoglein 1&2 staining was concentrated at the apical portion of the lateral plasma membrane. We suggest that the reorganisation of these desmosomal cadherins is an important component of uterine epithelial receptivity and this relocation is under the control of the ovarian hormone progesterone.

Expression of glucosamine trisaccharides on the rat uterine surface is altered by clomiphene citrate. III. Relationship with implantation regimes and pregnancy

The present study further elucidates the complex effects of a commonly-prescribed fertility drug upon a target organ in an animal model. In the human condition, its effects are rarely observed without the influence of endogenous ovarian hormones. The aim of the study was to investigate how the administration of a single dose of clomiphene citrate (CC) given prior to an implantation-priming sequence of ovarian hormones would affect the expression of surface oligosaccharides and membrane architecture of uterine epithelium. Ovariectomized rats were given a single dose of either 0.25 mg or 1.25 mg of CC prior to a hormone-priming regime of progesterone (P4) for 3 days with a single additional administration of oestradiol 17beta (E2) on day 3. Animals were killed 24 h after final treatment. Uterine tissue was labelled with the lectin Phytolacca americana conjugated with avidin, subsequently labelled with biotinylated ferritin and prepared for transmission electron microscopy. Results indicate that CC, when administered prior to the implantation hormone-priming regime, is able to act as a super oestrogen and upregulates expression of oligosaccharides on the plasma membrane surface and increases the density and length of microvilli on the surface of the cells when compared with other treatment regimes. Understanding of the effects of CC at the uterine level at the time of implantation enables manipulation of uterine receptivity to control fertility and to improve the outcome of assisted reproductive procedures.

Changes in oviductal morphology of the skink,Lampropholis guichenoti, associated with egg production

We describe changes in the morphology of the oviductal epithelium of an oviparous skink, Lampropholis guichenoti, during the course of egg production and oviposition: to characterize the luminal epithelial changes; to provide a baseline for understanding uterine changes in viviparous species; and to establish whether the plasma membrane transformation of uterine epithelial cells is indeed a feature restricted to viviparous species. Oviducts from vitellogenic, gravid, and postgravid females were observed using scanning electron microscopy. Cellular characteristics of the oviductal epithelium previously used to determine the plasma membrane transformation were assessed morphologically. Three anatomically different areas were defined within the oviduct, but no plasma membrane transformation was observed in the oviparous skink, suggesting that this is a phenomenon particular to viviparity.

Viviparous lizard,Eulamprus tympanum, shows changes in the uterine surface epithelium during early pregnancy that are similar to the plasma membrane transformation of mammals

The "plasma membrane transformation" describes a series of ultrastructural, biochemical, and morphological changes that occur in the uterus of many mammals at the time of blastocyst attachment. These changes, regardless of placental type or length of gestation, include alterations to microvillar length and density and the presence or absence of pinopods or uterodomes. Scanning electron microscopy (SEM) was used to 1) document the topographical ultrastructure of the uterus of Eulamprus tympanum, an eastern Australian viviparous skink with a simple chorioallantoic placenta, for the first time; and 2) determine whether changes identified as "plasma membrane transformation" in mammals occur in E. tympanum. Tissues collected over three seasons from nonreproductive subadult females, preovulatory, postovulatory, and early to mid-gestational females were examined. At low magnification the uterine epithelium of subadults displays a distinctive pattern of tissue folding that includes rectangular areas of tissue delineated by deep lateral and transverse folds. At higher magnification, the uterine epithelium surface is composed of two dominant cell types, i.e., those covered by microvilli and ciliated cells. The folding pattern observed in subadults is less evident in vitellogenic females and the cell surfaces appear highly secretory, with bulging cell apices. Tissue from postovulatory lizards has no distinctive folding pattern and cell surfaces are frequently smooth and lack microvilli. Uterine egg chambers lack ciliated cells at the embryonic pole, but display abundant secretory droplets. Thus, the uterus of E. tympanum undergoes a plasma membrane transformation. The scope of this transformation is not fully understood but may be related to the complexity of placental structure and the development of the embryo/fetus at parturition.

Cytoskeletal proteins in uterine epithelial cells only partially return to the pre-receptive state after the period of receptivity

Immunohistochemical staining of 5 cytoskeletal proteins (actin, alpha-actinin, gelsolin, plectin and plakoglobin) was used to investigate changes in distribution patterns of these proteins after the period of uterine receptivity for blastocyst implantation in the rat. Actin was found throughout the cytoplasm but it was concentrated along the apical plasma membrane on day 1 of pregnancy, decreased by day 6 and then increased again at day 9. Alpha-actinin and gelsolin were localized in distinctive bands along the apical plasma membrane at day 6 of pregnancy but became diffusely distributed at day 9. Plectin was localized along the apical and basal plasma membranes at day 6 but in higher amounts apically and at day 9, it was concentrated in apical and basal zones in the cells. Plakoglobin was found along the lateral and basal membranes with increased intensity along the apical third of the lateral plasma membrane from day 6 to day 9 of pregnancy. These results show that all 5 cytoskeletal proteins redistributed after the period of uterine receptivity: some exhibited a similar pattern of labelling to that found during the prereceptive state, whereas others only partially returned to the pre-receptive state. This change in distribution patterns may reflect differences in the epithelial barrier function before and after the period of receptivity.

Alterations in tight junction molecules of uterine epithelial cells during early pregnancy in the rat

Distribution patterns of the tight junction associated proteins ZO-1, claudin-1 and occludin were investigated in rat uterine epithelial cells during early pregnancy. Light microscopy and immunohistochemical labelling were used to detect these proteins on days 1, 3, 6 and 7 of pregnancy. Intense staining of claudin-1 at the apical region of the lateral plasma membrane accompanied diffuse staining throughout the cytoplasm. ZO-1 was also localised in the apical region, but ZO-1 was not present in the lower two thirds of the lateral plasma membrane or in the cytoplasm. Occludin was present only on days 6 and 7 of pregnancy. Labelling was also localised in the apical region of the lateral plasma membrane where tight junctions are known to be present. Our results show that ZO-1, claudin-1 and occludin are present in the apical region of uterine epithelial cells, and appear to play a role in the very dynamic tight-junctional network of uterine epithelial cells during early pregnancy. In particular, occludin appears only during uterine receptivity for implantation.

Stage-specific expression of the intermediate filament protein cytokeratin 13 in luminal epithelial cells of secretory phase human endometrium and peri-implantation stage rabbit endometrium

In preparation for blastocyst implantation, uterine luminal epithelial cells express new cell adhesion molecules on their apical plasma membrane. Since one mechanism epithelial cells employ to regulate membrane polarity is the establishment of specific membrane-cytoskeletal interactions, this study was undertaken to determine if new cytokeratin (CK) intermediate filament assemblies are expressed in endometrial epithelial cells during developmental stages related to blastocyst implantation. Type-specific CK antibodies were used for immunocytochemical and immunoblot analyses of 1) intermediate filament networks of the endometrial epithelium during embryo implantation in rabbits and 2) proliferative and secretory phases of the human menstrual cycle. CK18, a type I CK found in most simple epithelia, was expressed in all luminal and glandular epithelial cells of both the human and rabbit endometrium at all developmental stages analyzed; it was also strongly expressed in trophectoderm of the implanting rabbit blastocyst. In contrast, CK13, another type I cytokeratin, exhibited a regulated expression pattern in luminal, but not glandular, epithelial cells of secretory phase human and peri-implantation stage rabbit endometrium. Furthermore, in the rabbit implantation chambers, CK13 was predominantly localized at the cell apex of luminal epithelial cells, where it assembled into a dense filamentous network. These data suggest that the stage-specific expression of CK13 and a reorganization of the apical intermediate filament cytoskeleton of uterine luminal epithelial cells may play important functions in preparation for the implantation process.

Evolution of viviparity: what can Australian lizards tell us?

Historically, Australia has been important in the study of, and the development of hypotheses aimed at understanding, the evolution of viviparity in amniote vertebrates. Part of the importance of Australia in the field results from a rich fauna of skinks, including one of the broadest ranges of diversity of placental structures within one geographic region. During the last decade, we have focussed our studies on one lineage, the Eugongylus group of skinks of the subfamily Lygosominae because it contains oviparous species and some that exhibit complex placentae. Our specific objective has been to attempt to understand the fundamental steps required when viviparity, and ultimately complex placentae, evolve from oviparous ancestors. We have taken a three-prong approach: (1) detailed study of the morphology and ontogeny of the placentae of key species at the light microscope level; (2) study of changes in the uterus associated with pregnancy, or the plasma membrane transformation; and (3) measures of the net exchange of nutrients across the placenta or eggshell of key species. In turn, we have found that: (1) details of the morphology and ontogeny of placentae are more complex that originally envisaged, and that the early conclusions about a sequence in the evolution of complex placentae was naïve; (2) a plasma membrane transformation occurs in viviparous, but not oviparous lizards, and thus may be a fundamental feature of the evolution of viviparity in amniotes; and (3) species with more complex chorioallantoic placentae tend to transport more nutrients across the placenta during pregnancy than those with simpler chorioallantoic placentae but, because the correlation is not tight, the importance of the omphaloplacenta in transporting nutrients may have been overlooked. Also, the composition of yolk of highly matrotrophic species is broadly similar, but not identical, to the yolk of oviparous species. Some of the interpretation of our data within the context of our specific objective is not yet possible, pending the publication of a robust phylogeny of Eugongylus group skinks. Once such a phylogeny is available, we are in a position to propose specific hypotheses about the evolution of viviparity that can be tested using another lineage of amniotes, possibly Mabuya group skinks.

Characteristics of the uterine luminal surface epithelium at preovulatory and preimplantation stages in the marmoset monkey

Light and electron microscopy was used to examine the apical luminal epithelial surface of the uterus at preovulatory and preimplantation stages in the marmoset monkey. Luminal surface charge, detected by cationic ferritin staining, progressively decreased from preovulation to day 11 of pregnancy. The smooth, regular apical plasma membrane at preovulatory stages was in contrast to the convoluted, irregular surface observed during early pregnancy, especially at 1 day before blastocyst implantation. Profiles of microvilli were also altered, becoming thicker and more irregular during early pregnancy. Within the epithelial cell body, cyclic morphologic changes were seen, largely in association with secretory organelles. Giant phagocytic bodies were prominent at all stages examined, although their composition and intensity of staining varied throughout the cycle. Weak to moderate estrogen alpha and progesterone receptor immunostaining of the luminal epithelium was found during preovulatory and early pregnancy stages. This study describes complex cyclic changes in the morphology and biochemical make-up of the uterine luminal epithelial surface in a New World monkey in preparation for blastocyst attachment.

A successful pregnancy following SEM fine tuning of hormonal priming

BACKGROUND: Manipulation of the uterine epithelium utilising standard dose exogenous oestrogen (E2) and progesterone (P4) has been shown to achieve a mature secretory morphological response. However, in an in vitro fertilisation (IVF) setting, frozen embryo transfer (ET) has had a low success rate. We propose that in patients with previously failed ET attempts, the uterine epithelium can be directly visualised by biopsy and Scanning Electron Microscopy (SEM) and that with an individualised fine tuning of the hormone supplementation regime, based on the SEM examination of sequential uterine biopsies, it is possible to provide a uterine environment conducive to successful ET. METHODS: A 47 year old women was chosen for endometrial biopsy, histopathological dating and endometrial observation utilising SEM to determine the integrity of her secretory uterine epithelium because of her age and several previously failed attempts at frozen ET. Exogenous E2 and P4 supplementation was administered in modified doses according to the SEM result, in consecutive cycles until the epithelial response appeared satisfactory for potential implantation. RESULTS: This case study demonstrates the dramatic change in epithelial characteristics that can be achieved as a response to these altered doses of E2 and P4. The uterine morphology changed from a hypotrophic to a mature, receptive epithelium such that ET resulted in the birth of healthy twin boys. CONCLUSION: The comparison between the consecutive biopsies in direct response to the SEM analysis and tailored modification of E2 and P4 dose clearly demonstrates, in this case, the effectiveness of individual morphological monitoring to maximise the successful outcome of ET.

The plasma membrane transformation facilitates pregnancy in both reptiles and mammals

Mechanisms of placentation are very diverse in mammals and range from types in which the uterine epithelium is breached by the implanting blastocyst to those where the epithelium remains intact. Despite these differences in mechanisms, the initial response of the plasma membrane of uterine epithelial cells is remarkably similar across mammalian species which has led to the term 'plasma membrane transformation' to encapsulate the concept of a common beginning to implantation. Membrane phenomena similar to those of mammals have now been observed in some viviparous lizards at the ultrastructural level during early pregnancy, and we propose extending the concept of 'plasma membrane transformation' to lizards with live birth.

Increased adhesiveness in cultured endometrial-derived cells is related to the absence of moesin expression

Human endometrial epithelial cells (EECs) are nonadhesive for embryos throughout most of the menstrual cycle. During the so-called implantation window, the apical plasma membrane of EECs acquire adhesive properties by undergoing a series of morphological and biochemical changes. The human endometrial-derived epithelial cell line, RL95-2, serves as an in vitro model for receptive uterine epithelium because of its high adhesiveness for trophoblast-derived cells. In contrast, the HEC-1-A cell line, which displays poor adhesive properties for trophoblast cells, is considered to be less receptive. The ezrin, radixin, and moesin protein family members, which are present underneath the apical plasma membrane, potentially act to link the cytoskeleton and membrane proteins. In the present study, we have further investigated the adhesive features in these two unrelated endometrial-derived cell lines using an established in vitro model for embryonic adhesion. We have also analyzed the protein pattern and mRNA expression of ezrin and moesin in RL95-2 cells versus HEC-1-A cells. The results demonstrate that RL95-2 cells were indeed more receptive (81% blastocyst adhesion) compared with HEC-1-A cells (46% blastocyst adhesion). An intermediate adhesion rate was found in primary EECs cultured on extracellular matrix gel, thus allowing a partial polarization of these cells (67% blastocyst adhesion). Furthermore, we found that moesin was absent from RL95-2 cells. In contrast, ezrin is expressed in both cell lines, yet it is reduced in adherent RL95-2 cells. Data are in agreement with the hypothesis that uterine receptivity requires down-regulation or absence of moesin, which is a less-polarized actin cytoskeleton.

Expression of glucosamine trisaccharides on the rat uterine surface is altered by clomiphene citrate. II. Combination with ovarian hormones

We used a single administration of clomiphene citrate (CC), a synthetic oestrogen that is prescribed for infertility treatment, in combination with either a single administration of oestradiol 17beta (E2) or progesterone (P4) to assess the combined effects of these hormones on the uterine surface. The aim of these experiments was to investigate how CC in combination with these hormones affected both expression of oligosaccharides on the uterine surface and membrane architecture further elucidating CC's agonistic/antagonistic properties. Ovariectomized sexually mature rats were given combinations of E2 and CC (E2 + CC) or P4 and CC (P4 + CC) or P4 and E2 (P4 + E2) and were killed 24 h later. Uterine tissue was labelled with the lectin Phytolacca americana conjugated with avidin and subsequently labelled with biotinylated ferritin and prepared for transmission electron microscopy. Results of the administration of these hormone combinations indicate that CC, when administered in conjunction with E2, had the ability to downregulate expression of oligosaccharides on the membrane surface caused by E2. When administered with P4, CC had the ability to upregulate the effects of P4. Thus, when combined with E2, CC has an antagonistic effect but when combined with P4, CC has an agonistic effect.

Distributional changes of purinergic receptor subtypes (P2X 1-7) in uterine epithelial cells during early pregnancy

Expression of each of the purinergic receptor subtypes (P2X7) was studied by immunohistochemical localization in the apical, lateral and basal plasma membranes of rat uterine epithelial cells during early pregnancy to the time of implantation on Day 6. Labelling for each P2X subtype was seen in the apical, lateral and basal compartments on Days 1 and 3, except for P2X2 which was only observed in the basement membrane. The P2X5 signal was similar in temporal and spatial expression to the other subtypes, but with a greatly reduced intensity. At the time of implantation on Day 6, this pattern altered dramatically. Apical expression markedly increased for most subtypes while the lateral and basal signals were markedly reduced. The exceptions to this pattern were P2X2, which displayed both a strong basal and apical label, and P2X4 which became de-expressed in all areas. We propose that the changing spatial and temporal expression of the P2X receptors is a significant factor in the regulation of events during early pregnancy. They are expressed in the same location as remodelling. apoptosis, and protein activation events prior to implantation on Day 6. These observations suggest an up-regulation of calcium-mediated events, including cytoskeletal alterations, a decrease in luminal pH and transmembrane molecule activation.

Differential expression of insulin-like growth factors in the uterine epithelium and extracellular matrix during early pregnancy

We have studied the simultaneous expression of insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II) in the uterine epithelium and extracellular matrix during the time of trophoblast attachment and implantation. These studies reveal that IGF-I and IGF-II display different spatial and temporal patterns of expression during early pregnancy, and suggest a role for them in the process of attachment and implantation. Specifically, IGF-I is strongly expressed in the basal lamina which is the site of trophoblast invasion into the maternal stroma, and also in the apical epithelium, the site of initial trophoblast attachment. IGF-II is expressed to a lesser extent in the basal lamina, lateral plasma membranes and apical epithelium on day 3 but is only prominent apically at the time of implantation, suggesting a role in attachment.

Expression of glucosamine trisaccharides on the rat uterine surface is altered by clomiphene citrate

We have studied histochemically the effects of clomiphene citrate on the expression of oligosacchrides on the apical plasma membrane of uterine epithelial cells using the lectin Phytolacca americana. Ovariectomized sexually mature rats were given a single injection of either clomiphene in two concentrations or estradiol 17 beta or progesterone and were killed 24 hr later. Uterine tissue was labeled with Phytolacca americana conjugated with avidin and subsequently labeled with biotinalyted ferritin and prepared for transmission electron microscopy. Our results indicate that clomiphene and to a lesser degree progesterone significantly increased lectin binding. However, the increase was not as large as that observed with a single dose of estrodiol 17 beta. When the proportion of lectin positivity in relation to total membrane length was analyzed, treatment with clomiphene and progesterone did not have significantly different effects. Low dose clomiphene did not have a significant effect as compared with controls. Our data show that clomiphene has a dose-dependent adverse effect on lectin binding as compared with ovarian hormones. We suggest that these effects contribute to low pregnancy rates with clomiphene use.

Ultrastructural studies of glycan changes in the apical surface of the uterine epithelium during pre-ovulatory and and pre-implantation stages in the marmoset monkey

It has been postulated that carbohydrates are involved in a variety of cell-cell interactions including blastocyst implantation. In primates, there are only limited investigations on the ultrastructural localisation of the cyclic changes in uterine epithelial surface carbohydrates. Our aim was to investigate such changes during the pre-ovulatory and pre-implantation stages of the reproductive cycle in the marmoset monkey. After fixation of endometrial tissues, avidin-ferritin lectin cytochemistry was employed for apical surface glycan detection at the ultrastructural level. Five lectins were used including Canavalia ensiformis (Con A), Lotus tetragonolobus (LTA), Glycine max (SBA), Phytolacca americana (PWM) and Triticum vulgaris (WGA). Morphometry was used to quantitate changes in the intensity of lectin staining by determining the total number of ferritin particles per unit length of membrane. Surface and intra-cytoplasmic vesicles, stained by the lectins, were also examined. Quantitative ferritin assessment showed that 1 day before presumed implantation (days 11 to 12 after ovulation in the marmoset monkey) there was a significant increase in Con A, LTA and SBA staining on the apical uterine epithelial plasma membrane compared to the pre-ovulatory phase and earlier stages of pregnancy (days 4-8 after ovulation). A significant increase in PWM was also detected from early pregnancy to pre-implantation stages. All lectins except WGA produced reproducible staining within reproductive cycle groups. The greatest variation and intensity of epithelial surface staining was observed with WGA and the weakest with LTA. The patchy staining with LTA compared with thick coverage by WGA indicated the complexity of the carbohydrate arrangement in the glycocalyx of the uterine surface plasma membrane. Reduction of WGA reactivity after neuraminidase treatment suggested that the lectin binding might be related to the presence of heavily sialylated apical uterine membrane glycoconjugates. This is the first high-resolution study in primates to report quantitative cyclic changes in fucosyl, galactosyl, glucosyl, and mannosyl sugar residues of the apical uterine epithelial glycocalyx. The findings support the concept that uterine epithelial glycocalyx surface carbohydrates play a role in preparing a receptive uterine surface.

Junctional plaque proteins shift to the apical surface of uterine epithelial cells during early pregnancy in the rat

Antibodies against the cytoplasmic plaque molecules, plectin and plakoglobin, and cytokeratin, the molecular component of intermediate filaments (IFs), were used to examine the distribution of these molecules in rat uterine epithelial cells during early pregnancy including the period of blastocyst implantation. On day 1 of pregnancy plectin was detected in concentrated bands along the apical and basal plasma membranes, and diffusely throughout the cytoplasm. Plakoglobin was found along the entire lateral plasma membrane on day 1. By day 6, the time of blastocyst implantation, plectin was localised along the apical and basal membranes and reduced in the basal cytoplasm, and plakoglobin was seen exclusively at the apical-most quarter of the lateral plasma membrane. Cytokeratin was detected throughout the cytoplasm on day 1, but by day 6, was localised to the apical region of the cytoplasm only. These results show a redistribution of plectin, plakoglobin and cytokeratin away from the basal region of the uterine epithelial cells. The change in distribution of these molecules may contribute to the adhesion of the blastocyst to the apical and lateral surfaces of uterine epithelial cells and the subsequent detachment of the uterine epithelium from the basal lamina.

Pan-cadherin concentrates apically in uterine epithelial cells during uterine closure in the rat

The ubiquitous cadherin probe, pan-cadherin was used to study changes in the distribution of cadherins in the plasma membrane of rat uterine epithelial cells during early pregnancy when the uterine lumen closes down. A major reorganisation of cadherin expression was observed to occur in uterine epithelial cells between days 1 and 6 of pregnancy with a clear shift in molecular distribution from a basal location on day 1 to a distinctly and almost exclusively apical distribution by day 6 of pregnancy when the blastocyst is attached. We suggest these results indicate participation of this molecule in closure of the uterine lumen, a phenomenon well-known to occur in the rat uterus during early pregnancy and in which apical surfaces of opposing uterine epithelial cells cohere.

Actin-binding proteins undergo major alterations during the plasma membrane transformation in uterine epithelial cells

BACKGROUND

The apical surface of uterine epithelial cells undergoes a dramatic transformation during early pregnancy. Previous studies have shown that cytoskeletal actin microfilaments are associated with this transformation, but little is known of the role played by actin-binding proteins or which of the many described in other cell types are present in uterine epithelial cells.

METHODS

Immunohistochemical staining using monoclonal antibodies raised against four different actin-binding proteins (alpha-actinin, tropomyosin, gelsolin, and vinculin) was used to study the changing distribution of these proteins in uterine epithelium during early pregnancy in the rat.

RESULTS

Findings indicated the presence of all four of the actin-binding proteins in the uterine epithelium. The distribution of tropomyosin remained unchanged over the period of early pregnancy. Gelsolin and alpha-actinin displayed similarity in distribution. Day 1 showed an apicobasal localisation of reaction product, which by day 6 of pregnancy had concentrated into a thick band across the luminal surface of the cells. Vinculin staining was a diffuse band at the level of the basal plasma membrane at day 1 and became a diffuse faint band across the apical part of the cells on day 6.

CONCLUSIONS

This study confirms the presence of actin-binding proteins in uterine epithelial cells, and these findings are discussed in light of known ultrastructural alterations in the uterine epithelium during early pregnancy. Elucidation of the role of the actin-based cytoskeleton in the uterine epithelium may further our understanding of the dynamics of this unique environment that allows the implantation of a blastocyst.