Nuclear pore complex proteins mark the implantation window in human endometrium

Histological endometrial dating: a reliable tool for personalized frozen-thawed embryo transfer in patients with repeated implantation failure in natural cycles

OBJECTIVE

To evaluate the clinical availability and stability of histological endometrial dating as a tool for personalized frozen-thawed embryo transfer (pFET) in patients with repeated implantation failure (RIF) in natural cycles.

METHODS

A total of 1245 RIF patients were recruited to the present study. All of the patients received an endometrial dating evaluation on day 7 post-ovulation (PO + 7) to guide their first pFET. The second and third pFETs were executed according to histological examination (again employing biopsy) or by reference to previous results. Subsequent pregnancy outcomes for all of the cycles were ultimately tracked.

RESULTS

The out-of-phase rate for RIF patients was 32.4% (404/1245) and the expected dating rate (the probability of the expected endometrial dating aligning with repeat biopsy) for endometrial dating reevaluation was as high as 94.3% (50/53). The clinical pregnancy rates of first, second, and third pFETs were 65.3%, 50.0%, and 44.4%, respectively; and the cumulative clinical pregnancy rate attained 74.9% after three transfers. Endometrial dating reevaluations met expectations with more than a 2-year duration in three cases and elicited favorable clinical outcomes.

CONCLUSION

We validated the relatively high stability of the histological endometrial dating platform-including the out-of-phase rate and the expected dating rate of reevaluation in patients with RIF-by expanding the sample size. The pFET, based on histological endometrial dating, was of acceptable clinical value and was worthy of promotion in patients with unexplained RIF.

A Transient Mystery: Nucleolar Channel Systems

The nucleus is a complex organelle with functions beyond being a simple repository for genomic material. For example, its actions in biomechanical sensing, protein synthesis, and epigenomic regulation showcase how the nucleus integrates multiple signaling modalities to intricately regulate gene expression. This innate dynamism is underscored by subnuclear components that facilitate these roles, with elements of the nucleoskeleton, phase-separated nuclear bodies, and chromatin safeguarding by nuclear envelope proteins providing examples of this functional diversity. Among these, one of the lesser characterized nuclear organelles is the nucleolar channel system (NCS), first reported several decades ago in human endometrial biopsies. This tubular structure, believed to be derived from the inner nuclear membrane of the nuclear envelope, was first observed in secretory endometrial cells during a specific phase of the menstrual cycle. Reported as a consistent, yet transient, nuclear organelle, current interpretations of existing data suggest that it serves as a marker of a window for optimal implantation. In spite of this available data, the NCS remains incompletely characterized structurally and functionally, due in part to its transient spatial and temporal expression. As a further complication, evidence exists showing NCS expression in fetal tissue, suggesting that it may not act exclusively as a marker of uterine receptivity, but rather as a hormone sensor sensitive to estrogen and progesterone ratios. To gain a better understanding of the NCS, current technologies can be applied to profile rare cell populations or capture transient structural dynamics, for example, at a level of sensitivity and resolution not previously possible. Moving forward, advanced characterization of the NCS will shed light on an uncharacterized aspect of reproductive physiology, with the potential to refine assisted reproductive techniques.

Presence of endometrial nucleolar channel systems at the time of frozen embryo transfer in hormone replacement cycles with successful implantation

OBJECTIVE

To detect nucleolar channel systems (NCSs) in cells in endometrial aspirations obtained immediately before embryo transfer during blastocyst hormone replacement therapy-frozen embryo transfer (HRT-FET) cycles without affecting implantation.

DESIGN

Prospective case series.

SETTING

University-affiliated fertility clinic.

PATIENTS

Five patients who underwent an HRT-FET cycle consented to lower uterine segment aspiration using an open-tip embryo transfer catheter during a routine mock transfer performed immediately before embryo transfer.

INTERVENTIONS

Exfoliated cells in the aspirated endometrial secretions were analyzed for the presence of NCSs using indirect immunofluorescence and, in one case, electron microscopy for unambiguous identification.

MAIN OUTCOME MEASURES

On the basis of a previous study, positive NCS status was defined as the presence of NCSs in at least 3 endometrial epithelial cells (EECs). The effect of endometrial aspiration on implantation and pregnancy outcomes was assessed.

RESULTS

Biochemical pregnancy, as evidenced by positive β-human chorionic gonadotropin, was seen in 5 of 5 patients, and clinical pregnancy was seen in 2 of 5 patients. NCSs were detected in exfoliated EECs of uterine secretions in 4 of 5 patient samples and could not be unequivocally identified in 1 of 5 patient samples, which was designated as indeterminate.

CONCLUSIONS

This is the first report of NCS detection in HRT-FET cycles in the absence of follicular development and ovulation. NCS status can be determined in exfoliated EECs of uterine secretions obtained at the time of embryo transfer while maintaining implantation. Our study furthers the goal of establishing whether individualized point of care testing of NCS status in HRT-FET cycles can determine optimal endometrial receptivity and improve pregnancy outcomes.

Proteomic profile of preeclampsia in the first trimester of pregnancy

OBJECTIVE

Preeclampsia (PE) is a leading cause of pregnancy-associated maternal and neonatal morbidity and mortality. Detection of patients at risk before the clinical onset of PE is a priority. Proteomics have become a valuable tool for the discovery of new biomarkers; however, the understanding of the underlying mechanism is necessary. The aim of the study was to determine differences between proteomic serum profiles of PE and normotensive pregnancies using quantitative and qualitative approaches.

STUDY DESIGN

Serum samples from pregnant women were taken at 10-12 weeks of gestation with follow-up to determine PE development. Samples were analyzed using nano 2-D liquid chromatography UPLC and qTOF-MS/MS.

RESULTS

A total of 136 women were recruited, of which eight (5.9%) developed PE, and eight normotensive were randomly selected as a control group for comparison. A different profile was obtained between groups. Nine proteins showed quantitative differences with fold-change over 1.5: PRRC2C (217.02), HEATR5A (179.46), ATP6 (162.38), PRRC2B (83.09), RBM25 (5.36), NUP205 (3.38), HLA-I (2.27), ZC3H13 (2.15), and SREK1 (1.66); and two under 0.66: Importin-4 (0.55) and Cytochrome b (0.26). Using bilateral Fisher's exact test for the qualitative approach, LRRK1 had statistical significance (p = .044), while PRRC2B (p = .121), PRRC2C (p = .134), and NUP205 (p = .134) showed a tendency to be present in PE.

CONCLUSION

The found proteins have plausibility with the early pathophysiological events that have been associated with this pathology. Further studies should be performed to confirm these findings and elucidate their specific roles.

Human Endometrial Transcriptome and Progesterone Receptor Cistrome Reveal Important Pathways and Epithelial Regulators

CONTEXT

Poor uterine receptivity is one major factor leading to pregnancy loss and infertility. Understanding the molecular events governing successful implantation is hence critical in combating infertility.

OBJECTIVE

To define Progesterone Receptor (PGR)-regulated molecular mechanisms and epithelial roles in receptivity.

DESIGN

RNA-sequencing and PGR-ChIP-seq were conducted in parallel to identify PGR-regulated pathways during the Window of implantation (WOI) in endometrium of fertile women.

SETTING

Endometrial biopsies from the proliferative and mid-secretory phases were analyzed.

PATIENTS OR OTHER PARTICIPANTS

Participants were fertile, reproductive aged (18-37 years) women with normal cycle length, and without any history of dysmenorrhea, infertility, or irregular cycles. In total, 42 endometrial biopsies obtained from 42 women were analyzed in this study.

INTERVENTIONS

There were no interventions during this study.

MAIN OUTCOME MEASURES

Here we measured the alterations in gene expression and PGR occupancy in the genome during the WOI, based on the hypothesis that PGR binds uterine chromatin cycle dependently to regulate genes involved in uterine cell differentiation and function.

RESULTS

653 genes were identified with regulated PGR binding and differential expression during the WOI. These were involved in regulating inflammatory response, xenobiotic metabolism, epithelial mesenchymal transition, cell death, interleukin/Signal Transducer And Activator Of Transcription (STAT) signaling, estrogen response, and Mammalian target of rapamycin complex 1 (MTORC1) response. Transcriptome of the epithelium identified 3052 differentially expressed genes, of which 658 were uniquely regulated. Transcription factors Interferon Regulatory Factor 8 (IRF8) and Myocyte Enhancer Factor 2C (MEF2C) were found to be regulated in the epithelium during the WOI at the protein level, suggesting potentially important functions that are previously unrecognized.

CONCLUSION

PGR binds the genomic regions of genes regulating critical processes in uterine receptivity and function.

Nucleoplasmic Reticulum Formation in Human Endometrial Cells is Steroid Hormone Responsive and Recruits Nascent Components

The nuclei of cells may exhibit invaginations of the nuclear envelope under a variety of conditions. These invaginations form a branched network termed the nucleoplasmic reticulum (NR), which may be found in cells in pathological and physiological conditions. While an extensive NR is a hallmark of cellular senescence and shows associations with some cancers, very little is known about the formation of NR in physiological conditions, despite the presence of extensive nuclear invaginations in some cell types such as endometrial cells. Here we show that in these cells the NR is formed in response to reproductive hormones. We demonstrate that oestrogen and progesterone are sufficient to induce NR formation and that this process is reversible without cell division upon removal of the hormonal stimulus. Nascent lamins and phospholipids are incorporated into the invaginations suggesting that there is a dedicated machinery for its formation. The induction of NR in endometrial cells offers a new model to study NR formation and function in physiological conditions.

Functional polymorphism within NUP210 encoding for nucleoporin GP210 is associated with the risk of endometriosis

OBJECTIVE

To investigate whether nucleoporin 210 (GP210, encoded by NUP210 gene) is involved in endometriosis.

DESIGN

Immunohistofluorescence analysis for assessing whether GP210 is expressed in endometrial tissues from patients and controls; genotyping and case-control study for assessing the association between rs354476 within NUP210 and risk of endometriosis; in vitro luciferase assay for assessing the functional activity of rs354476.

SETTING

University.

PATIENT(S)

Histologically diagnosed cases (n = 175) of endometriosis: minimal or mild (stage I-II) in 48 cases (28%), moderate (stage III) in 69 cases (39%), and severe (stage IV) in 58 cases (33%). Controls (n = 557) were female blood donors collected at Meyer Hospital of Florence.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

GP210 tissue expression; genotype distribution and risk of endometriosis; in vitro gene expression measurements.

RESULT(S)

GP210 had positive nuclear immunohistofluorescence staining in endometrial glandular epithelium. Carriers of the variant allele were associated with increased risks: C/T, odds ratio (OR) 1.83, 95% confidence interval (CI) 1.04-3.21; T/T, OR 2.55, 95% CI 1.36-4.80. In vitro, luciferase assay showed that rs354476 is a bona fide target for hsa-miR-125b-5p.

CONCLUSION(S)

Nucleoporin GP210 is involved in endometriosis. Rs354476 polymorphism affects the regulation of NUP210 gene expression by altering the binding with hsa-miR-125b-5p, a microRNA already known as playing an important role for endometriosis. This provides the rationale for the observed increased risk of endometriosis in carriers of the variant allele.

Emerging roles for nucleoporins in reproductive cellular physiology 1

Nucleoporins are a specialized subset of nuclear proteins that comprise the nuclear pore complex and regulate nucleocytoplasmic transport. Recent demonstrations of roles for individual nucleoporins in multiple paradigms of differentiation via mechanisms independent of nuclear trafficking represent conceptual advances in understanding the contributions of nucleoporins to cellular development. Among these, a functional role for nucleoporins in reproductive fitness and gametogenesis has been identified, supported by robust models and clinical studies that leverage the power of next generation sequencing technology to identify reproductive-disease-associated mutations in specific nucleoporins. Proper nucleoporin function manifests in different ways during oogenesis and spermatogenesis. However, nonhuman models of gametogenesis may not recapitulate human mechanisms, which may confound translational interpretation and relevance. To circumvent these limitations, identification of reproductive pathologies in patients, combined with next generation sequencing approaches and advanced in silico tools, offers a powerful approach to investigate the potential function of nucleoporins in human reproduction. Ultimately, elucidating the role of nucleoporins in reproductive biology will provide opportunities for predictive, diagnostic, and therapeutic strategies to address reproductive disorders.

A historical review of blastocyst implantation research

Research development on blastocyst implantation was reviewed in three sections: primate implantation, ungulate farm animal implantation, and the general process of blastocyst implantation in small rodents. Future research directions of this area are suggested.

Minimum values for midluteal plasma progesterone and estradiol concentrations in patients who achieved pregnancy with timed intercourse or intrauterine insemination without a human menopausal gonadotropin

Objective

The aim of the study was to assess the lower limits of midluteal plasma progesterone and estradiol concentrations in patients who achieved pregnancy with timed intercourse or intrauterine insemination without a human menopausal gonadotropin stimulation.

Results

We included 297 pregnant cycles of 297 women and assessed midluteal plasma progesterone and estradiol concentrations and pregnancy outcomes, retrospectively. These cycles were compared with the non-pregnant cycles (406 cycles) of the same women who became pregnant. Mean midluteal plasma P4 and E2 concentrations were significantly (P < 0.01) higher in pregnant cycles (14.5 and 188.5 pg/mL) than in non-pregnant cycles (10.7 and 162.6 pg/mL). The 5 percentiles of progesterone and estradiol in pregnant cycles were 5.6 and 70.2 pg/mL, respectively. The lowest progesterone and estradiol levels in pregnant cycles were 2.3 and 23.4 pg/mL, respectively. In non-pregnant cycles, many women had low P4 levels that were less than 5.6 ng/mL. Subgroup analyses showed slight differences among the four groups, which may have been due to the ovarian function of each group. Miscarriage was not related to progesterone and estradiol concentrations. These values may be useful for the evaluation of necessary values for pregnancy with timed intercourse or intrauterine insemination.

Status of nucleolar channel systems in uterine secretions accurately reflects their prevalence-a marker for the window of implantation-in simultaneously obtained endometrial biopsies

OBJECTIVE

To assess whether nucleolar channel systems (NCSs) can be detected in exfoliated endometrial epithelial cells (EECs) of uterine secretions and whether such noninvasively determined NCS status is associated with significant NCS prevalence in simultaneously obtained endometrial biopsies.

DESIGN

Prospective study (December 2015-February 2017).

SETTING

University-affiliated and private fertility clinics.

PATIENT(S)

Luteal-phase patients of reproductive age requiring endometrial biopsy for medical indications.

INTERVENTION(S)

Uterine secretion aspiration before endometrial biopsy. Cells in uterine secretions were spun onto slides and fixed. NCSs were identified and quantified in cells and paraffin-embedded tissue sections by indirect immunofluorescence.

MAIN OUTCOME MEASURE(S)

Comparison of NCS status of uterine secretions with NCS prevalence in biopsies. Based on NCS detection, uterine secretions were assigned a status of NCS-positive (n = 15) or NCS-negative (n = 7). NCS prevalence in biopsies was expressed as a percentage of NCSs per EECs.

RESULT(S)

NCSs can be detected in exfoliated EECs of uterine secretions. Median NCS prevalence in endometrial biopsies from patients with NCS-positive secretions was 41.9% (interquartile range [IQR], 21.1-53.9) versus 2.0% (IQR, 0-6.9) when secretions were NCS-negative. The NCS status of secretions identified a significant difference in NCS prevalence of simultaneously obtained biopsies.

CONCLUSION(S)

NCS status of secretions accurately reflects NCS prevalence of biopsies, a marker for the implantation window. As secretion aspiration is compatible with same-day ET, our study provides proof of principle for a minimally invasive approach to determine endometrial receptivity for timing frozen ET.

Shared mechanisms in physiological and pathological nucleoplasmic reticulum formation

The mammalian nuclear envelope (NE) can develop complex dynamic membrane-bounded invaginations in response to both physiological and pathological stimuli. Since the formation of these nucleoplasmic reticulum (NR) structures can occur during interphase, without mitotic NE breakdown and reassembly, some other mechanism must drive their development. Here we consider models for deformation of the interphase NE, together with the evidence for their potential roles in NR formation.

Compartmentalized gene expression profiling of receptive endometrium reveals progesterone regulated ENPP3 is differentially expressed and secreted in glycosylated form

The complexity of endometrial receptivity at the molecular level needs to be explored in detail to improve the management of infertility. Here, differential expression of transcriptomes in receptive endometrial glands and stroma revealed Ectonucleotide Pyrophosphatase/Phosphodiesterase 3 (ENPP3) as a progesterone regulated factor and confirmed by various methods, both at mRNA and protein level. The involvement of ENPP3 in embryo attachment was tested in an in vitro model for human embryo implantation. Interestingly, there was high expression of ENPP3 mRNA in stroma but not protein. Presence of N-glycosylated ENPP3 in receptive phase uterine fluid in women confirms its regulation by progesterone and makes it possible to use in a non-invasive test of endometrial receptivity.

Expression of DNAJB12 or DNAJB14 causes coordinate invasion of the nucleus by membranes associated with a novel nuclear pore structure

DNAJB12 and DNAJB14 are transmembrane proteins in the endoplasmic reticulum (ER) that serve as co-chaperones for Hsc70/Hsp70 heat shock proteins. We demonstrate that over-expression of DNAJB12 or DNAJB14 causes the formation of elaborate membranous structures within cell nuclei, which we designate DJANGOS for DNAJ-associated nuclear globular structures. DJANGOS contain DNAJB12, DNAJB14, Hsc70 and markers of the ER lumen and ER and nuclear membranes. Strikingly, they are evenly distributed underneath the nuclear envelope and are of uniform size in any one nucleus. DJANGOS are composed primarily of single-walled membrane tubes and sheets that connect to the nuclear envelope via a unique configuration of membranes, in which the nuclear pore complex appears anchored exclusively to the outer nuclear membrane, allowing both the inner and outer nuclear membranes to flow past the circumference of the nuclear pore complex into the nucleus. DJANGOS break down rapidly during cell division and reform synchronously in the daughter cell nuclei, demonstrating that they are dynamic structures that undergo coordinate formation and dissolution. Genetic studies showed that the chaperone activity of DNAJ/Hsc70 is required for the formation of DJANGOS. Further analysis of these structures will provide insight into nuclear pore formation and function, activities of molecular chaperones, and mechanisms that maintain membrane identity.

Progesterone Threshold Determines Nucleolar Channel System Formation in Human Endometrium

Nucleolar channel systems (NCSs), micron-sized organelles specific to nuclei of human endometrial epithelial cells (EECs), are robust markers of the midluteal phase under the apparent control of progesterone. To gain further insight into the role of progesterone in NCS formation, we quantitatively assessed their sensitivity to oral contraceptive pills (OCPs) using immunofluorescence-based detection of NCSs. Comparison of endometrial biopsies and serum progesterone levels on cycle day (CD) 10 and 20 (LH +6/7) of 6 naturally cycling women and 6 OCP users demonstrated that OCPs interfered with NCS formation on CD20, their natural peak presence. Although this confirmed prior observation based on electron microscopic sampling, OCPs unexpectedly induced limited but distinct amounts of NCSs already on CD10, when they are never present in natural cycles. Thus, OCPs can cause secretory changes in the endometrium during the proliferative phase. In a novel finding, robust NCS formation on CD20 was dependent on a 4 ng/mL progesterone threshold but did not correlate linearly with serum progesterone levels. Given the threshold being close to that serving as evidence for ovulation, NCSs can serve as ovulation markers.

Premature formation of nucleolar channel systems indicates advanced endometrial maturation following controlled ovarian hyperstimulation

STUDY QUESTION

Is there a shift in the timing of nucleolar channel system (NCS) formation following controlled ovarian hyperstimulation (COH)?

SUMMARY ANSWER

NCSs appear prematurely following COH compared with natural cycles.

WHAT IS KNOWN ALREADY

During natural cycles, NCSs of endometrial epithelial cell (EEC) nuclei are exclusively present during the window of implantation and are uniformly distributed throughout the upper endometrial cavity.

STUDY DESIGN, SIZE, DURATION

Prospective two-cohort study. Cohorts I and II each consisted of seven volunteers for the duration of three menstrual study cycles that were separated by at least one wash-out or rest cycle, between December 2008 and May 2012.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Participants were recruited from a pool of healthy oocyte donors. Consecutive endometrial biopsies were obtained during the same luteal phase on cycle days (CD) 16, 20 and 26 for Cohort I, and on CD14, 22 and 24 for Cohort II, following random assignment to a natural cycle group, a COH cycle group (using a GnRH antagonist), or a COH cycle group receiving luteal phase hormonal supplementation (COH + S). The day of oocyte retrieval was designated CD14 in COH cycles and the day of the LH surge was designated CD13 in natural cycles. Prevalence of NCSs in the nuclei of EECs was quantified using indirect immunofluorescence with an antibody directed against a subset of related nuclear pore complex proteins that are major constituents of NCSs. Progesterone and estradiol levels were measured on the day of each endometrial biopsy.

MAIN RESULTS AND THE ROLE OF CHANCE

The natural cycle group exhibited peak NCS prevalence on CD20 [53.3%; interquartile range (IQR) 28.5-55.8], which rapidly declined on CD22 (11.8%; IQR 6.3-17.6), CD24 (2.5%; IQR 0.0-9.2) and CD26 (0.3%; IQR 0.0-3.5), and no NCSs on CD14 and 16 defining a short NCS window around CD20. In contrast, in COH and COH + S cycles, NCS prevalence was high already on CD16 (40.4%; IQR 22.6-53.4 and 35.6%; IQR 26.4-44.5, respectively; P = 0.001 compared with CD16 of the natural cycle group, Mann-Whitney), whereas no significant difference in NCS prevalence was detected on any of the other five CDs between the three groups (P > 0.05).

LIMITATIONS, REASONS FOR CAUTION

The cohort size was small (n = 7) but was offset by the all-or-none presence of NCSs on CD16 in natural versus COH and COH + S cycles and the fact that each subject served as her own control.

WIDER IMPLICATIONS OF THE FINDINGS

Premature appearance of NCSs and hence maturation of the endometrium following COH is consistent with previous studies based on histological dating but contradicts studies based on mRNA expression profiling, which reported a lag in endometrial maturation. However, this is the first study of this kind that is based on consecutive endometrial biopsies within the same cycle and that reports such clear-cut differences: no versus robust NCS presence on CD16. Our observation of advanced endometrial maturation following COH may contribute to the reduced implantation rates seen in fresh compared with frozen and donor IVF-embryo transfer cycles. Therefore, the NCS window could serve as a sensitive guide for timing of embryo transfer in frozen and donor cycles.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by the March of Dimes Birth Defects foundation (1-FY09-363 to U.T.M.); Ferring Pharmaceuticals, Parsippany, NJ; East Coast Fertility, Plainview, NY and the CMBG Training Program (T32 GM007491 to M.J.S.). We report no competing interests.

Assessing receptivity in the endometrium: the need for a rapid, non-invasive test

Successful implantation of an embryo into the uterus requires synchrony between the blastocyst and the endometrium. Endometrial preparedness, or receptivity, occurs only for a very short time during the mid-secretory phase of the menstrual cycle in fertile women. Failure to achieve receptivity results in infertility and is a rate-limiting step for IVF success. Frozen embryo transfer in non-stimulation cycles is already improving live birth rates. However, an important tool that is missing in the armoury of reproductive specialists is a means to rapidly assess endometrial receptivity, either during initial assessment or immediately prior to embryo transfer. The development of a wealth of omics technologies now opens the way for identifying potential receptivity markers, although validation of these is still a major issue. This review assesses the current state of the field and the requirements to proceed to a valid clinical test.

Quantification of nucleolar channel systems: uniform presence throughout the upper endometrial cavity

OBJECTIVE

To determine the prevalence of nucleolar channel systems (NCSs) by uterine region, applying continuous quantification.

DESIGN

Prospective clinical study.

SETTING

Tertiary care academic medical center.

PATIENT(S)

Forty-two naturally cycling women who underwent hysterectomy for benign indications.

INTERVENTION(S)

NCS presence was quantified by a novel method in six uterine regions-fundus, left cornu, right cornu, anterior body, posterior body, and lower uterine segment (LUS)-with the use of indirect immunofluorescence.

MAIN OUTCOME MEASURE(S)

Percentage of endometrial epithelial cells (EECs) with NCSs per uterine region.

RESULT(S)

NCS quantification was observer independent (intraclass correlation coefficient 0.96) and its intrasample variability low (coefficient of variation 0.06). Eleven of 42 hysterectomy specimens were midluteal, ten of which were analyzable with nine containing >5% EECs with NCSs in at least one region. The percentage of EECs with NCSs varied significantly between the LUS (6.1%; interquartile range [IQR] 3.0-9.9) and the upper five regions (16.9%; IQR 12.7-23.4), with fewer NCSs in the basal layer of the endometrium (17 ± 6%) versus the middle (46 ± 9%) and luminal layers (38 ± 9%) of all six regions.

CONCLUSION(S)

NCS quantification during the midluteal phase demonstrates uniform presence throughout the endometrial cavity, excluding the LUS, with a preference for the functional luminal layers. Our quantitative NCS evaluation provides a benchmark for future studies and further supports NCS presence as a potential marker for the window of implantation.

The nucleolar channel system reliably marks the midluteal endometrium regardless of fertility status: a fresh look at an old organelle

OBJECTIVE

To determine whether nucleolar channel systems (NCSs) in the midluteal endometrium are associated with overall fertility status and/or with unexplained infertility.

DESIGN

Retrospective and prospective clinical studies.

SETTING

Repository of stored specimens from prior multicenter study and private infertility center.

PATIENT(S)

Retrospective study that included 97 women (49 fertile couples, 48 infertile couples) who had been randomized for endometrial biopsy during the midluteal or late luteal phase. The prospective study included 78 women with a variety of infertility diagnoses.

INTERVENTION(S)

Endometrial biopsies were obtained and assessed for the presence of NCSs by indirect immunofluorescence.

MAIN OUTCOME MEASURE(S)

The presence of NCS was graded semiquantitatively and dichotomized as normal versus low or absent.

RESULT(S)

Normal presence of NCS was significantly associated with the midluteal phase compared with the late luteal phase (80% vs. 29%). However, there was no association between presence of NCS and fertility status or between presence of NCS and unexplained infertility.

CONCLUSION(S)

Midluteal phase endometrium consistently forms NCSs regardless of fertility status, including unexplained infertility. This indicates a possible role for the NCS in initiating the window of endometrial receptivity. However, the consistent presence of NCSs across several different types of infertility challenges the likelihood that inadequate secretory transformation is a cause of infertility.