The mid-secretory endometrial transcriptomic landscape in endometriosis: a meta-analysis

STUDY QUESTION

Do women with endometriosis have a different endometrial gene expression profile at the time of embryo implantation than women without endometriosis?

SUMMARY ANSWER

The endometrial gene expression profile of women with endometriosis differs from that of women without endometriosis at the mid-secretory phase, although the differences are small.

WHAT IS KNOWN ALREADY

About 50% of women with endometriosis suffer infertility. Several molecular studies have suggested impaired endometrial receptivity in women with endometriosis, while others have detected no dysregulation of endometrial receptivity. Nevertheless, the previous endometrial transcriptome studies comparing women with and without endometriosis have been performed in small sample size with limited statistical power. We set out to systematically search and compile data of endometrial gene expression signatures at the receptive phase in women with endometriosis versus control women. Based on the obtained data, we conducted a meta-analysis of differentially expressed genes in order to raise the power of the analysis for identifying the molecular profiles of receptive phase endometria in endometriosis.

STUDY DESIGN, SIZE, DURATION

A systematic literature search was conducted up to February 2022 following PRISMA criteria and included PubMed, Cochrane and Web of Science databases. For the systematic search, the term ‘endometriosis’ was paired with the terms ‘transcriptomics’, ‘transcriptome’, ‘gene expression’, ‘RNA-seq’, ‘sequencing’ and ‘array’, by using the Boolean operator ‘AND’ to connect them. Articles written in English were screened and interrogated for data extraction.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A meta-analysis was performed on the selected studies to extract the differentially expressed genes described at the mid-secretory phase in women with endometriosis versus women without endometriosis in natural cycles, using the robust rank aggregation method. In total, transcriptome data of 125 women (78 patients and 47 controls) were meta-analysed, with a special focus on endometrial receptivity-specific genes based on commercial endometrial receptivity tests.

MAIN RESULTS AND THE ROLE OF CHANCE

In total, 8 studies were eligible for the quantitative meta-analysis, gathering transcriptome data from the mid-secretory phase endometria of 125 women. A total of 7779 differentially expressed transcripts between the study groups were retrieved (3496 up-regulated and 4283 down-regulated) and were meta-analysed. After stringent multiple correction, there was no differential expression of any single molecule in the endometrium of women with endometriosis versus controls, while enrichment analysis detected that the pathways of chemotaxis and locomotion are dysregulated in endometriosis. Further analysis of endometrial receptivity-specific genes highlighted dysregulation of C4BPA, MAOA and PAEP and enrichment of immune and defence pathways in women with endometriosis.

LIMITATIONS, REASONS FOR CAUTION

Most of the studies included into the meta-analysis were relatively small and had different study designs, which might have contributed to a bias.

WIDER IMPLICATIONS OF THE FINDINGS

The current meta-analysis supports the hypothesis that endometrial receptivity is altered in women with endometriosis, although the changes are small. The molecules and pathways identified could serve as future biomarkers and therapeutical targets in detecting and treating endometriosis-associated infertility.

STUDY FUNDING/COMPETING INTEREST(S)

The authors declare no competing interests. This work was supported by the Spanish Ministry of Education, Culture and Sport [grant FPU15/01193] and the Margarita Salas program for the Requalification of the Spanish University system [grant UJAR01MS]; Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and European Regional Development Fund (FEDER): grants RYC-2016-21199 and ENDORE SAF2017-87526-R; Programa Operativo FEDER Andalucía (B-CTS-500-UGR18; A-CTS-614-UGR20); the Junta de Andalucía [BIO-302; and PAIDI P20_00158]; the University of Jaén [PAIUJA-EI_CTS02_2017]; the University of Granada, Plan Propio de Investigación 2016, Excellence actions: Units of Excellence; Unit of Excellence on Exercise and Health (UCEES), and by the Junta de Andalucía, Consejería de Conocimiento, Investigación y Universidades and European Regional Development Fund (ERDF), ref. SOMM17/6107/UGR; the Estonian Research Council (grant PRG1076); Horizon 2020 innovation (ERIN, grant no. EU952516) of the European Commission and Enterprise Estonia (grant EU48695).

TRIAL REGISTRATION NUMBER

The systematic review was registered at PROSPERO (identifier: CRD42020122054).

P–403 Sodium tungstate increases embryo adhesion through a direct effect on endometrial cells

Study question

Does sodium tungstate treatment induce a change in endometrial cells’ capacity to implant trophoblasts?

Summary answer

Administration of sodium tungstate to endometrial cells increases trophoblast adhesion.

What is known already

Sodium tungstate (ST) has shown its capacity to modulate the activity of cytokines, such as leptin, an activator of an obligatory signalling cascade in the embryo-implantation process. STAT3, a signal transducer molecule critical for the embryo implantation process, is also known to be activated by ST. Still, ST’s effect on implantation using biological systems has never been studied. Embryo implantation process and endometrium roles are complicated to study in vivo due to a lack of animal models and appropriate techniques. In vitro techniques using immortalised cell lines allows a first approach to study early implantation stages, such as embryo adhesion.

Study design, size, duration

An in vitro study was carried out using a human endometrial carcinoma cell line (HEC–1-A) treated with sodium tungstate for 24 and 48h, and choriocarcinoma cell spheroids (JAr). Different times of treatment and concentrations were studied. Each experiment was performed in triplicate.

Participants/materials, setting, methods

Confluent endometrial HEC–1-A cultures were treated with ST at concentrations (0–150mM) and withaferin A (1mM), negative control for embryo adhesion. After the treatment period, HEC–1-A cultures were washed with ST-free culture medium to eliminate ST. Immediately, 15 JAr trophoblast spheroids were added to cultures and coincubated with gentle agitation for 30, 60 and 90 minutes. An inverted light microscope was used to count adhered and floating spheroids, and determine the trophoblast adherence ratio.

Main results and the role of chance

HEC–1-A cells treated with ST showed normal morphology and growth at all doses except 150mM. At the highest dose tested, the cells’ culture was still viable (negative blue trypan staining) and maintained morphology, but the adhesion to the plate surface was affected. Doses from 0.15 to 15mM were used to perform adhesion assays.

HEC–1-A cells treated with ST for 24h showed an increased capacity to adhere JAr trophoblast spheroids. Adhesion rates reached significant differences at doses of 1.5 and 15mM after 60 and 90 minutes of coincubation. After 90 minutes, untreated cells reached 32.8% adhesion rate, while 1.5 and 15mM ST-treated cells reached 54.6% and 53.4% respectively (p < 0.05 ST vs untreated). Thus, the increment of trophoblast adhesion rate induced by ST reached 66%. Lower adhesion rates were observed after 60 minutes of coincubation but were also significant with a relative increase of 49.1% at 1.5mM and 50.5% at 1.5mM when compared with untreated cells (p < 0.05)

Longer treatments (48h) showed similar trends to 24h-treatments, but with a lower extent of ST effect on HEC–1-A receptivity. Maximum adhesion rates were also observed at 90 minutes of coincubation and 1.5 and 15mM doses. The Mean adhesion rate increase was >40% with both doses. Limitations, reasons for caution: The current study is the first approach to evaluate sodium tungstate effect on endometrium using an in vitro model. Future research using in vivo models should be performed to assess sodium tungstate effect on endometrium receptivity and its potential as a fertility treatment.

Wider implications of the findings: We conclude that the direct effect of sodium tungstate on endometrial cells increases embryo adhesion rate. These results open a new research line to a potential treatment in human reproduction management with sodium tungstate to solve the unmet need of inducing embryo implantation.

Trial registration number

Not applicable

P–171 Automated oocyte and zygote denudation using a novel microfluidic device supervised by a computer vision algorithm

Study question

Is it possible to remove cumulus cells using a 16-well microfluidic device with automated flows to facilitate vitrification, ICSI, NI-PGT or non-invasive metabolomics analysis?

Summary answer

The designed automated system and protocol efficiently denude 16 samples simultaneously with a x10 lower shear stress than the manual process and without human intervention.

What is known already

Most processes involved in IVF such as insemination, washing, denudation, embryo culture and selection are still manually performed, labor-intensive and require highly skilled professionals. This leads to a significant variability in the clinical outcomes achieved by different embryologists and labs. The automation of these processes is a promising approach to reduce costs and improve the accessibility to assisted reproductive therapies. Although a simple procedure, standardization of cumulus oocyte complex (COCs) and zygotes denudation is key to facilitate ICSI, vitrification and to avoid DNA contamination for NI-embryo testing (PGT or metabolomics), while avoiding damage to the oocyte by excessive shear stress.

Study design, size, duration

A total of 160 cow COCs were used due to their size similarity with human COCs. Half were denuded 16–20 hours post-insemination and half pre-insemination for 5–10 minutes. COCs were classified as partially denuded if fertilization assessment, ICSI or vitrification was possible, and completely denuded if no cumulus cells remained. COCs controls were manually denuded (Stripper® capillary 145μm ID) to compare shear stress between procedures. This study was conducted during 2020 – 2021.

Participants/materials, setting, methods

We developed a customized microfluidic biochip that exerts a particular fluid motion while avoiding egg entrapment within microfluidic channels. The denudation efficacy was established by subjectively scoring images of bovine oocytes after generating a continuous “Push & Pull” fluid motion inside the biochip wells. A Computer Vision model was developed in parallel in order to optically assess denudation completion. The model used was a Pytorch implementation of Faster-RCNN with ImageNet pretrained weights

Main results and the role of chance

96 bovine COCs were microfuidically handled post insemination achieving complete (56/96) or partial (40/96) removal of the cumulus cells on day 1, while for day 3 double denudation group, 89/96 (92.7%) were completely denuded while the rest remained partially denuded. In comparison, 80/80 (100%) of manually denuded cow COCs, achieved complete denudation (50% post-insemination group and 50% pre-insemination group). In addition, 48/64 (75%) cow COCs treated pre-insemination were partially denuded, enough to carry out ICSI after 5–10 min of treatment. The results here obtained indicate that media needs to flow through the device at a rate that can generate enough shear to strip off the cumulus-corona cells while avoiding emptying of the reservoirs containing the fertilization or culture medium. The shear stress of our design was calculated to be smaller than 4.4 Pa, about ten times lower than the one applied by the manual process (∼44Pa). The deep learning algorithm was tested on 20 unseen human oocytes on day 1, with 10 true positives 9 true negatives, and 1 false negative (95% accuracy).

Limitations, reasons for caution

The success of the denudation procedure was dependent on the design of the biochip wells and the microfluidic protocol used. The accuracy of our findings is still limited because of the difficulty in manufacturing prototype biochips.

Wider implications of the findings: Complete denudation is key to avoid DNA contamination for NI-PGT or metabolomics analysis, while avoiding damage to the oocyte by excessive shear stress. Our device, which has the potential of scaling up and treat each oocyte individually, can improve automation and increase efficiency of current ART procedures

Trial registration number

NA

Transcriptome of early embryonic invasion at implantation sites in a murine model

Successful implantation relies on the interaction between a competent embryo and a receptive endometrium. The aim of the present study was to investigate genes differentially expressed in early invasive embryonic tissue versus decidual tissue in mice. Samples were obtained from the ectoplacental cone, the immediately surrounding deciduas and from deciduas from interimplantation sites. Microarray analysis showed that 817 genes were differentially expressed between extra-embryonic tissue and the surrounding decidua and that 360 genes were differentially expressed between the different deciduas, with a high representation of developmental processes. Genes differentially expressed in the maternal compartment included chemokines, lipoproteins, growth factors and transcription factors, whereas the embryonic invasive tissue expressed genes commonly observed in invasive tumour-like processes. These results provide information about genes involved in early embryonic invasion and the control exerted by the surrounding decidua. This information may be useful to find targets involved in pathologies associated with implantation failure and early pregnancy loss.

In vitro culture of mouse embryos reduces differential gene expression between inner cell mass and trophectoderm

Differences in gene expression and imprinting have been reported, comparing in vivo versus in vitro generated preimplantation embryos. Furthermore, mouse studies have shown that placenta development is altered following in vitro culture. However, the molecular mechanisms underlying these findings are unknown. We therefore isolated trophectoderm (TE) and inner cell mass (ICM) cells from in vivo and in vitro fertilization (IVF) embryos and evaluated their transcriptome using microarrays. We found that the transcriptomes of in vitro produced ICM and TE cells showed remarkably few differences compared to ICM and TE cells of in vivo generated embryos. In vitro fertilization embryos showed a reduced number of TE cells compared to in vivo embryos. In addition, TE of IVF embryos showed significant downregulation of solute transporter genes and of genes involved in placenta formation (Eomesodermin, Socs3) or implantation (Hbegf). In summary, IVF and embryo culture significantly affects the transcriptome of ICM and TE cells.

Effect of ICSI on gene expression and development of mouse preimplantation embryos

BACKGROUND

In vitro culture (IVC) and IVF of preimplantation mouse embryos are associated with changes in gene expression. It is however not known whether ICSI has additional effects on the transcriptome of mouse blastocysts.

METHODS

We compared gene expression and development of mouse blastocysts produced by ICSI and cultured in Whitten's medium (ICSI(WM)) or KSOM medium with amino acids (ICSI(KSOMaa)) with control blastocysts flushed out of the uterus on post coital Day 3.5 (in vivo). In addition, we compared gene expression in embryos generated by IVF or ICSI using WM. Global pattern of gene expression was assessed using the Affymetrix 430 2.0 chip.

RESULTS

Blastocysts from ICSI fertilization have a reduction in the number of trophoblastic and inner cell mass cells compared with embryos generated in vivo. Approximately 1000 genes are differentially expressed between ICSI blastocyst and in vivo blastocysts; proliferation, apoptosis and morphogenetic pathways are the most common pathways altered after IVC. Unexpectedly, expression of only 41 genes was significantly different between embryo cultured in suboptimal conditions (WM) or optimal conditions (KSOM(aa)).

CONCLUSIONS

Our results suggest that fertilization by ICSI may play a more important role in shaping the transcriptome of the developing mouse embryo than the culture media used.

Unique transcriptome, pathways, and networks in the human endometrial fibroblast response to progesterone in endometriosis

Eutopic endometrium in endometriosis has molecular evidence of resistance to progesterone (P(4)) and activation of the PKA pathway in the stromal compartment. To investigate global and temporal responses of eutopic endometrium to P(4), we compared early (6-h), intermediate (48-h), and late (14-Day) transcriptomes, signaling pathways, and networks of human endometrial stromal fibroblasts (hESF) from women with endometriosis (hESF(endo)) with hESF from women without endometriosis (hESF(nonendo)). Endometrial biopsy samples were obtained from subjects with and without mild peritoneal endometriosis (n = 4 per group), and hESF were isolated and treated with P(4) (1 μM) plus estradiol (E(2)) (10 nM), E(2) alone (10 nM), or vehicle for up to 14 days. Total RNA was subjected to microarray analysis using a Gene 1.0 ST (Affymetrix) platform and analyzed by using bioinformatic algorithms, and data were validated by quantitative real-time PCR and ELISA. Results revealed unique kinetic expression of specific genes and unique pathways, distinct biological and molecular processes, and signaling pathways and networks during the early, intermediate, and late responses to P(4) in both hESF(nonendo) and hESF(endo), although a blunted response to P(4) was observed in the latter. The normal response of hESF to P(4) involves a tightly regulated kinetic cascade involving key components in the P(4) receptor and MAPK signaling pathways that results in inhibition of E(2)-mediated proliferation and eventual differentiation to the decidual phenotype, but this was not established in the hESF(endo) early response to P(4). The abnormal response of this cell type to P(4) may contribute to compromised embryonic implantation and infertility in women with endometriosis.

Endometrial gene expression analysis at the time of embryo implantation in women with unexplained infertility

Successful embryo implantation depends on the quality of the embryo, as well as on the receptivity of the endometrium. The aim of this study was to investigate the endometrial gene expression profile in women with unexplained infertility in comparison with fertile controls at the time of embryo implantation in order to find potential predictive markers of uterine receptivity and to identify the molecular mechanisms of infertility. High-density oligonucleotide gene arrays, comprising 44 000 gene targets, were used to define the endometrial gene expression profile in infertile (n = 4) and fertile (n = 5) women during the mid-secretory phase (day LH + 7). Microarray results were validated using real-time PCR. Analyses of expression data were carried out using non-parametric methods. Hierarchical clustering and principal component analysis showed a clear distinction in endometrial gene expression between infertile and fertile women. In total we identified 145 significantly (>3-fold change) up-regulated and 115 down-regulated genes in infertile women versus controls. Via Database for Annotation, Visualization and Integrated Discovery functional analysis we detected a substantial number of dysregulated genes in the endometria of infertile women, involved in cellular localization (21.1%) and transport (18.8%) and transporter activity (13.1%) and with major localization in extracellular regions (19.2%). Ingenuity Pathways Analysis of the gene list showed dysregulation of gene pathways involved in leukocyte extravasation signalling, lipid metabolism and detoxification in the endometria of infertile women. In conclusion, endometrial gene expression in women with unexplained infertility at the time of embryo implantation is markedly different from that in fertile women. These results provide new information on genes and pathways that may have functional significance as regards to endometrial receptivity and subsequent embryo implantation.

CXCL10 and IL-6 induce chemotaxis in human trophoblast cell lines

The investigation of trophoblast chemoattractive molecules in humans is of high interest for the reproductive field. Current evidence in ruminants demonstrates that CXCL10, formerly the interferon-gamma-inducible protein 10 (IP-10), is a potent chemotactic molecule implicated in the migration of trophoblast cells during early gestation. The aim of this work was to explore the existence of CXCL10/CXCR3 in the human model. Furthermore, chemotaxis assays were performed to demonstrate CXCL10 chemotactic activity in the human trophoblast cell lines JEG-3 and AC-1M88. Surprisingly, the conditioned media from epithelial endometrial cells (EEC) induced the highest trophoblast migration rate. Cytokine and chemokine membrane protein arrays were used to identify the secreted protein profile of EEC-conditioned media, and IL-6 was found to be the most abundant and CXCL13 the second most abundant molecule. Using a chemotaxis assay on AC-IM88, IL-6 antibody blocked the effect of EEC, indicating IL-6 to be an effective chemoattractive factor for trophoblast cells in the human model.

Wide genomic analysis of human endometrial receptivity: new times, new opportunities

Microarray technology has broadened the insight into many research fields allowing scientists to analyse the expression of many genes in quick and efficient experiments aimed at translating these findings into clinical applications. In reproductive medicine, researchers have exploited microarrays to increase understanding of the molecular mechanisms involved in endometrial receptivity and how a possible therapeutic translation can be feasible. In the last 4 years, several studies have focused on the genomics of the human endometrium in different physiological and pathological conditions, and these studies have generated a large amount of information about the regulation and dysregulation of the window of implantation (WOI) genes in fertile, subfertile and refractory conditions. However, the key molecules/mechanisms in endometrial receptivity remain to be elucidated. In this comprehensive review, we have analysed the available results obtained in our own and other laboratories, defining the genomic profile of the receptive endometrium in different situations and its possible clinical application.

Identification, characterization and co-localization of label-retaining cell population in mouse endometrium with typical undifferentiated markers

BACKGROUND

The endometrium, lining of the uterus, is a highly active organ that is remodelled periodically during the lifespan. Different studies suggest the presence of an adult or progenitor stem cell (PSC) population in this tissue because of its cyclic regenerative capacity.

METHODS

In this study, we aim at identifying and localizing the putative PSC population in the murine uterus using the 5-bromo-2'-deoxyuridine (BrdU) labelling method to detect label-retaining cells (LRCs) that cycle slowly. Uteri from BrdU-treated mice were analysed via single and double immunohistochemistry to co-localize them with the markers of undifferentiation already described such as c-KIT and POU5F1 (also known as OCT-4). Finally, we confirmed the presence of the indicated markers at mRNA level.

RESULTS

We observed the presence and gradual decrease of LRCs in the endometrium during the lifespan of the mice. In adulthood, the LRC population decreased notably and remained in the lower region of the stroma in the murine endometrium. Some of the endometrial LRCs co-localized with c-KIT and POU5F1. PCR and nested-PCR confirmed the presence of these undifferentiated markers.

CONCLUSIONS

We demonstrated that the murine endometrium possesses LRCs with the features of a putative PSC population localized at the lower region of the stroma.

Effect of an intrauterine device on the gene expression profile of the endometrium

CONTEXT

The human endometrium acquires the ability to allow embryo attachment just for a specific period of time during each menstrual cycle. Understanding of the opposite functional status, referred to as refractoriness, can potentially be used to improve receptivity in infertile patients or as an interceptive approach to prevent gestation.

OBJECTIVE

The objective of the study was to analyze the endometrial gene expression profile induced by an inert intrauterine device (IUD) at the time of implantation.

DESIGN

We used a microarray containing more than 16,000 cDNAs to investigate the gene expression profile of receptive vs. refractory endometrium in the same women induced by the presence of an IUD. We compared the gene expression profile of endometrium obtained at LH+7 (window of receptivity) from the same women (n = 5) at the following time points: month 1, corresponding to the natural cycle before IUD insertion; month 3, just before IUD removal; and months 5 and 15. Data were validated by quantitative RT-PCR for IGF binding protein-3, peroxisome proliferative activated receptor-gamma, glycodelin, and leukemia inhibitory factor and immunohistochemistry for glycodelin.

RESULTS

We identified 147 genes significantly dysregulated in the refractory endometrium (78 up- and 69 down-regulated). Interestingly, 52 of these genes have previously been reported to be regulated during window of implantation. Surprisingly, the majority of genes (96.6%) remained dysregulated 2 months after IUD removal, but 1 yr later most of them (80%) returned to normal.

CONCLUSIONS

Our results reveal that a refractory endometrium in a fertile woman produced by an IUD is induced by preventing the normal transition to a receptive gene expression profile through effects on a specific subset or cluster of genes that impact on endometrial receptivity.

Implantation of the human embryo: research lines and models. From the implantation research network 'Fruitful'

Infertility is an increasing problem all over the world, and it has been estimated that 10-15% of couples in fertile age have fertility problems. Likewise induced unsafe abortion is a serious threat to women's health. Despite advances made in assisted reproduction techniques, little progress has been made in increasing the success rate during fertility treatment. This document describes a wide range of projects carried out to increase the understanding in the field of embryo implantation research. The 'Fruitful' research network was created to encourage collaborations within the consortium and to describe our different research potentials to granting agencies or private sponsors.

Similar endometrial development in oocyte donors treated with either high- or standard-dose GnRH antagonist compared to treatment with a GnRH agonist or in natural cycles

BACKGROUND

This descriptive study evaluates the impact on endometrial development of standard and high doses of a GnRH antagonist in stimulated cycles compared with GnRH agonist and natural cycles.

METHODS

Thirty-one oocyte donors were treated with a combination of rFSH and 0.25 mg/day ganirelix (standard dose), 2 mg/day ganirelix (high dose) or 0.6 mg/day buserelin (long protocol). Vaginal progesterone (200 mg/day) was administered in the luteal phase. Endometrial biopsies were performed 2 and 7 days after HCG administration. Additional biopsies were carried out in a subset of 12 subjects, 2 and 7 days following the LH peak of their previous natural cycle. Biopsies were evaluated histologically and by scanning electron microscopy. Gene expression profiles were also studied.

RESULTS

At HCG +2, all the parameters studied were similar in all the groups and comparable to those observed in the natural cycle. At HCG +7, endometrial dating, steroid receptors and the presence of pinopodes were comparable in both GnRH antagonist groups and in the natural cycle. In buserelin group, endometrial dating and pinopode expression suggested an arrested endometrial development. For window of implantation genes, expression patterns were closer to those in the natural cycle following standard- or high-dose ganirelix than after buserelin administration.

CONCLUSION

No relevant alteration was observed in the endometrial development in the early and mid-luteal phases in women undergoing controlled ovarian stimulation for oocyte donation following daily treatment with a standard- or high-dose GnRH antagonist. In addition, the endometrial development after GnRH antagonist mimics the natural endometrium more closely than after GnRH agonist.

Leptin system in embryo development and implantation: a protein in search of a function

Implantation is a crucial moment in the reproduction process that requires perfect synchronization between the embryo and the maternal endometrium. The embryo must reach the blastocyst stage and the endometrium must be prepared to receive it. An appropriate and specific molecular dialogue must also take place between them. There is ample evidence to show that the leptin system is implicated in this cross-talk. Examples are described. Although there is some controversy surrounding the data, they are supported by the presence of leptin receptor mRNA in mouse and human oocytes and embryos throughout preimplantation development. Otherwise, the leptin mRNA is only detected at the blastocyst stage in both human and mouse. Furthermore, leptin is found at higher concentrations in the conditioned media from competent human blastocysts than in those from arrested embryos, suggesting that this molecule is a marker for blastocyst viability. Given that expression of the leptin receptor increases in the human endometrium during the luteal phase, the secreted leptin could trigger its activation. Finally, leptin and the leptin receptor have been detected in implantation sites. All these findings point to the involvement of the leptin system in the molecular mechanism of the implantation process and embryo development.

Analysis of early promoters of the Bacillus bacteriophage GA-1

Bacteriophage GA-1, which infects Bacillus sp. strain G1R, is evolutionarily related to phage phi29, which infects Bacillus subtilis. We report the characterization of several GA-1 promoters located at either end of its linear genome. Some of them are unique for GA-1 and drive the expression of open reading frames that have no counterparts in the genome of phi29 or related phages. These unique promoters are active at early infection times and are repressed at late times. In vitro transcription reactions revealed that the purified GA-1-encoded protein p6 represses the activity of these promoters, although the amount of p6 required to repress transcription was different for each promoter. The level of protein p6 produced in vivo increases rapidly during the first stage of the infection cycle. The protein p6 concentration may serve to modulate the expression of these early promoters as infection proceeds.

Phi29 family of phages

Continuous research spanning more than three decades has made the Bacillus bacteriophage phi29 a paradigm for several molecular mechanisms of general biological processes, such as DNA replication, regulation of transcription, phage morphogenesis, and phage DNA packaging. The genome of bacteriophage phi29 consists of a linear double-stranded DNA (dsDNA), which has a terminal protein (TP) covalently linked to its 5' ends. Initiation of DNA replication, carried out by a protein-primed mechanism, has been studied in detail and is considered to be a model system for the protein-primed DNA replication that is also used by most other linear genomes with a TP linked to their DNA ends, such as other phages, linear plasmids, and adenoviruses. In addition to a continuing progress in unraveling the initiation of DNA replication mechanism and the role of various proteins involved in this process, major advances have been made during the last few years, especially in our understanding of transcription regulation, the head-tail connector protein, and DNA packaging. Recent progress in all these topics is reviewed. In addition to phi29, the genomes of several other Bacillus phages consist of a linear dsDNA with a TP molecule attached to their 5' ends. These phi29-like phages can be divided into three groups. The first group includes, in addition to phi29, phages PZA, phi15, and BS32. The second group comprises B103, Nf, and M2Y, and the third group contains GA-1 as its sole member. Whereas the DNA sequences of the complete genomes of phi29 (group I) and B103 (group II) are known, only parts of the genome of GA-1 (group III) were sequenced. We have determined the complete DNA sequence of the GA-1 genome, which allowed analysis of differences and homologies between the three groups of phi29-like phages, which is included in this review.

Phi29 family of phages

Continuous research spanning more than three decades has made the Bacillus bacteriophage phi29 a paradigm for several molecular mechanisms of general biological processes, such as DNA replication, regulation of transcription, phage morphogenesis, and phage DNA packaging. The genome of bacteriophage phi29 consists of a linear double-stranded DNA (dsDNA), which has a terminal protein (TP) covalently linked to its 5' ends. Initiation of DNA replication, carried out by a protein-primed mechanism, has been studied in detail and is considered to be a model system for the protein-primed DNA replication that is also used by most other linear genomes with a TP linked to their DNA ends, such as other phages, linear plasmids, and adenoviruses. In addition to a continuing progress in unraveling the initiation of DNA replication mechanism and the role of various proteins involved in this process, major advances have been made during the last few years, especially in our understanding of transcription regulation, the head-tail connector protein, and DNA packaging. Recent progress in all these topics is reviewed. In addition to phi29, the genomes of several other Bacillus phages consist of a linear dsDNA with a TP molecule attached to their 5' ends. These phi29-like phages can be divided into three groups. The first group includes, in addition to phi29, phages PZA, phi15, and BS32. The second group comprises B103, Nf, and M2Y, and the third group contains GA-1 as its sole member. Whereas the DNA sequences of the complete genomes of phi29 (group I) and B103 (group II) are known, only parts of the genome of GA-1 (group III) were sequenced. We have determined the complete DNA sequence of the GA-1 genome, which allowed analysis of differences and homologies between the three groups of phi29-like phages, which is included in this review.

The switch from early to late transcription in phage GA-1: characterization of the regulatory protein p4G

The transcription program of the Bacillus phage GA-1, a distant relative of phage Phi29, has been studied. Transcription of the GA-1 genome occurred in two stages, early and late. Early genes were expressed from two promoters equivalent to the Phi29 A2b and A2c promoters, whereas late transcription started at a site equivalent to the Phi29 late A3 promoter. The activity of the GA-1 early A2b and A2c promoters diminished 10 minutes after infection, a time at which expression of the late promoter increased significantly. The switch from early to late transcription required protein synthesis, suggesting the need for viral protein(s). An open reading frame was found in the GA-1 genome coding for a protein showing a 53 % similarity to Phi29 regulatory protein p4, and was named p4G. In Phi29, protein p4 represses the early A2b and A2c promoters and activates the late A3 promoter by recruiting RNA polymerase to it. A binding site for protein p4Gwas localized upstream from the GA-1 late A3 promoter, overlapping with the early A2b promoter. In vitro, protein p4Gprevented the binding of RNA polymerase to the GA-1 early A2b promoter but, unlike in Phi29, had no effect on the expression of the late A3 promoter: RNA polymerase could efficiently bind and initiate transcription from the A3 promoter in the absence of protein p4G. Therefore, activation of late transcription occurs differently in GA-1 and Phi29. We propose that protein p4Gis an anti-repressor which inhibits the binding to the late promoter of an unknown repressor factor present in the host strain.