FGFR1 regulates trophectoderm development and facilitates blastocyst implantation

Interpreting regulatory mechanisms of Hippo signaling through a deep learning sequence model

Signaling pathway components are well studied, but how they mediate cell-type-specific transcription responses is an unresolved problem. Using the Hippo pathway in mouse trophoblast stem cells as a model, we show that the DNA binding of signaling effectors is driven by cell-type-specific sequence rules that can be learned genome wide by deep learning models. Through model interpretation and experimental validation, we show that motifs for the cell-type-specific transcription factor TFAP2C enhance TEAD4/YAP1 binding in a nucleosome-range and distance-dependent manner, driving synergistic enhancer activation. We also discovered that Tead double motifs are widespread, highly active canonical response elements. Molecular dynamics simulations suggest that TEAD4 binds them cooperatively through surprisingly labile protein-protein interactions that depend on the DNA template. These results show that the response to signaling pathways is encoded in the cis-regulatory sequences and that interpreting the rules reveals insights into the mechanisms by which signaling effectors influence cell-type-specific enhancer activity.

The impact of dynamic caudal type homeobox 2 expression on the differentiation of human trophoblast lineage during implantation

The trophoblast lineage differentiation represents a rate-limiting step in successful embryo implantation. Adhesion, invasion and migration processes within the trophoblast are governed by several transcription factors. Among them, CDX2 is a critical regulator shaping the destiny of the trophoblast. While its altered expression is a linchpin initiating embryo implantation in mice, the precise influence of CDX2 on the functionality and lineage differentiation of early human trophoblast remains unclear. In this study, we employed well-established human trophoblast stem cell (hTSC) lines with CDX2 overexpression coupled with a 3D in vitro culture system for early human embryos. We revealed that the downregulation of CDX2 is a prerequisite for syncytialization during human embryo implantation based on immunofluorescence, transcriptome analysis, CUT-tag sequencing and the construction of 3D human trophoblast organoids. While CDX2 overexpression inhibited syncytialization, it propelled hTSC proliferation and invasive migration. CDX2 exerted its influence by interacting with CGA, PTGS2, GCM1, LEF1 and CDH2, thereby hindering premature differentiation of the syncytiotrophoblast. CDX2 overexpression enhanced the epithelial-mesenchymal transition of human trophoblast organoids. In summary, our study provides insights into the molecular characteristics of trophoblast differentiation and development in humans, laying a theoretical foundation for advancing research in embryo implantation.

Diverse Fgfr1 signaling pathways and endocytic trafficking regulate mesoderm development

The fibroblast growth factor (FGF) pathway is a conserved signaling pathway required for embryonic development. Activated FGF receptor 1 (FGFR1) drives multiple intracellular signaling cascade pathways, including ERK/MAPK and PI3K/AKT, collectively termed canonical signaling. However, unlike Fgfr1-null embryos, embryos containing hypomorphic mutations in Fgfr1 lacking the ability to activate canonical downstream signals are still able to develop to birth but exhibit severe defects in all mesodermal-derived tissues. The introduction of an additional signaling mutation further reduces the activity of Fgfr1, leading to earlier lethality, reduced somitogenesis, and more severe changes in transcriptional outputs. Genes involved in migration, ECM interaction, and phosphoinositol signaling were significantly downregulated, proteomic analysis identified changes in interactions with endocytic pathway components, and cells expressing mutant receptors show changes in endocytic trafficking. Together, we identified processes regulating early mesoderm development by mechanisms involving both canonical and noncanonical Fgfr1 pathways, including direct interaction with cell adhesion components and endocytic regulation.

Maternal loss-of-function of Nlrp2 results in failure of epigenetic reprogramming in mouse oocytes

Background

NLRP2 belongs to the subcortical maternal complex (SCMC) of mammalian oocytes and preimplantation embryos. This multiprotein complex, encoded by maternal-effect genes, plays a pivotal role in the zygote-to-embryo transition, early embryogenesis, and epigenetic (re)programming. The maternal inactivation of genes encoding SCMC proteins has been linked to infertility and subfertility in mice and humans. However, the underlying molecular mechanisms for the diverse functions of the SCMC, particularly how this cytoplasmic structure influences DNA methylation, which is a nuclear process, are not fully understood.

Results

We undertook joint transcriptome and DNA methylome profiling of pre-ovulatory germinal-vesicle oocytes from Nlrp2-null, heterozygous (Het), and wild-type (WT) female mice. We identified numerous differentially expressed genes (DEGs) in Het and Nlrp2-null when compared to WT oocytes. The genes for several crucial factors involved in oocyte transcriptome modulation and epigenetic reprogramming, such as DNMT1, UHRF1, KDM1B and ZFP57 were overexpressed in Het and Nlrp2-null oocytes. Absence or reduction of Nlrp2, did not alter the distinctive global DNA methylation landscape of oocytes, including the bimodal pattern of the oocyte methylome. Additionally, although the methylation profile of germline differentially methylated regions (gDMRs) of imprinted genes was preserved in oocytes of Het and Nlrp2-null mice, we found altered methylation in oocytes of both genotypes at a small percentage of the oocyte-characteristic hyper- and hypomethylated domains. Through a tiling approach, we identified specific DNA methylation differences between the genotypes, with approximately 1.3% of examined tiles exhibiting differential methylation in Het and Nlrp2-null compared to WT oocytes.

Conclusions

Surprisingly, considering the well-known correlation between transcription and DNA methylation in developing oocytes, we observed no correlation between gene expression differences and gene-body DNA methylation differences in Nlrp2-null versus WT oocytes or Het versus WT oocytes. We therefore conclude that post-transcriptional changes in the stability of transcripts rather than altered transcription is primarily responsible for transcriptome differences in Nlrp2-null and Het oocytes.

Diverse Fgfr1 signaling pathways and endocytic trafficking regulate early mesoderm development

The Fibroblast growth factor (FGF) pathway is a conserved signaling pathway required for embryonic development. Activated FGF receptor 1 (FGFR1) drives multiple intracellular signaling cascade pathways, including ERK/MAPK and PI3K/AKT, collectively termed canonical signaling. However, unlike Fgfr1 null embryos, embryos containing hypomorphic mutations in Fgfr1 lacking the ability to activate canonical downstream signals are still able to develop to birth, but exhibit severe defects in all mesodermal-derived tissues. The introduction of an additional signaling mutation further reduces the activity of Fgfr1, leading to earlier lethality, reduced somitogenesis, and more severe changes in transcriptional outputs. Genes involved in migration, ECM-interaction, and phosphoinositol signaling were significantly downregulated, proteomic analysis identified changes in interactions with endocytic pathway components, and cells expressing mutant receptors show changes in endocytic trafficking. Together, we identify processes regulating early mesoderm development by mechanisms involving both canonical and non-canonical Fgfr1 pathways, including direct interaction with cell adhesion components and endocytic regulation.

FRS2-independent GRB2 interaction with FGFR2 is not required for embryonic development

FGF activation is known to engage canonical signals, including ERK/MAPK and PI3K/AKT, through various effectors including FRS2 and GRB2. Fgfr2FCPG/FCPG mutants that abrogate canonical intracellular signaling exhibit a range of mild phenotypes but are viable, in contrast to embryonic lethal Fgfr2-/- mutants. GRB2 has been reported to interact with FGFR2 through a non-traditional mechanism, by binding to the C-terminus of FGFR2 independently of FRS2 recruitment. To investigate whether this interaction provides functionality beyond canonical signaling, we generated mutant mice harboring a C-terminal truncation (T). We found that Fgfr2T/T mice are viable and have no distinguishable phenotype, indicating that GRB2 binding to the C-terminal end of FGFR2 is not required for development or adult homeostasis. We further introduced the T mutation on the sensitized FCPG background but found that Fgfr2FCPGT/FCPGT mutants did not exhibit significantly more severe phenotypes. We therefore conclude that, although GRB2 can bind to FGFR2 independently of FRS2, this binding does not have a critical role in development or homeostasis.

FRS2-independent GRB2 interaction with FGFR2 is not required for embryonic development

FGF activation is known to engage canonical signals, including ERK/MAPK and PI3K/AKT, through various effectors including FRS2 and GRB2. Fgfr2 FCPG/FCPG mutants that abrogate canonical intracellular signaling exhibit a range of mild phenotypes but are viable in contrast to embryonic lethal Fgfr2 -/- mutants. GRB2 has been reported to interact with FGFR2 through a non-traditional mechanism, by binding to the C-terminus of FGFR2 independently of FRS2 recruitment. To investigate if this interaction provides functionality beyond canonical signaling, we generated mutant mice harboring a C-terminal truncation (T). We found that Fgfr2 T/T mice are viable and have no distinguishable phenotype, indicating that GRB2 binding to the C-terminal end of FGFR2 is not required for development or adult homeostasis. We further introduced the T mutation on the sensitized FCPG background but found that Fgfr2 FCPGT/FCPGT mutants did not exhibit significantly more severe phenotypes. We therefore conclude that, while GRB2 can bind to FGFR2 independently of FRS2, this binding does not have a critical role in development or homeostasis.

FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

Deficiency of endothelial FGFR1 alleviates hyperoxia-induced bronchopulmonary dysplasia in neonatal mice

Disrupted neonatal lung angiogenesis and alveologenesis often give rise to bronchopulmonary dysplasia (BPD), the most common chronic lung disease in children. Hyperoxia-induced pulmonary vascular and alveolar damage in premature infants is one of the most common and frequent factors contributing to BPD. The purpose of the present study was to explore the key molecules and the underlying mechanisms in hyperoxia-induced lung injury in neonatal mice and to provide a new strategy for the treatment of BPD. In this work, we reported that hyperoxia decreased the proportion of endothelial cells (ECs) in the lungs of neonatal mice. In hyperoxic lung ECs of neonatal mice, we detected upregulated fibroblast growth factor receptor 1 (FGFR1) expression, accompanied by upregulation of the classic downstream signaling pathway of activated FGFR1, including the ERK/MAPK signaling pathway and PI3K-Akt signaling pathway. Specific deletion of Fgfr1 in the ECs of neonatal mice protected the lungs from hyperoxia-induced lung injury, with improved angiogenesis, alveologenesis and respiratory metrics. Intriguingly, the increased Fgfr1 expression was mainly attributed to aerosol capillary endothelial (aCap) cells rather than general capillary endothelial (gCap) cells. Deletion of endothelial Fgfr1 increased the expression of gCap cell markers but decreased the expression of aCap cell markers. Additionally, inhibition of FGFR1 by an FGFR1 inhibitor improved alveologenesis and respiratory metrics. In summary, this study suggests that in neonatal mice, hyperoxia increases the expression of endothelial FGFR1 in lung ECs and that deficiency of endothelial Fgfr1 can ameliorate hyperoxia-induced BPD. These data suggest that FGFR1 may be a potential therapeutic target for BPD, which will provide a new strategy for the prevention and treatment of BPD.

Paracrine interactions through FGFR1 and FGFR2 receptors regulate the development of preimplantation mouse chimaeric embryo

The preimplantation mammalian embryo has the potential to self-organize, allowing the formation of a correctly patterned embryo despite experimental perturbation. To better understand the mechanisms controlling the developmental plasticity of the early mouse embryo, we used chimaeras composed of an embryonic day (E)3.5 or E4.5 inner cell mass (ICM) and cleaving 8-cell embryo. We revealed that the restricted potential of the ICM can be compensated for by uncommitted 8-cell embryo-derived blastomeres, thus leading to the formation of a normal chimaeric blastocyst that can undergo full development. However, whether such chimaeras maintain developmental competence depends on the presence or specific orientation of the polarized primitive endoderm layer in the ICM component. We also demonstrated that downregulated FGFR1 and FGFR2 expression in 8-cell embryos disturbs intercellular interactions between both components and results in an inverse proportion of primitive endoderm and epiblast within the resulting ICM and abnormal embryo development. This finding suggests that FGF signalling is a key part of the regulatory mechanism that assigns cells to a given lineage and ensures the proper composition of the blastocyst, which is a prerequisite for its successful implantation in the uterus and for further development.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Pulling back the curtain: The hidden functions of receptor tyrosine kinases in development

Receptor tyrosine kinases (RTKs) are a conserved superfamily of transmembrane growth factor receptors that drive numerous cellular processes during development and in the adult. Upon activation, multiple adaptors and signaling effector proteins are recruited to binding site motifs located within the intracellular domain of the RTK. These RTK-effector interactions drive subsequent intracellular signaling cascades involved in canonical RTK signaling. Genetic dissection has revealed that alleles of Fibroblast Growth Factor receptors (FGFRs) that lack all canonical RTK signaling still retain some kinase-dependent biological activity. Here we examine how genetic analysis can be used to understand the mechanism by which RTKs drive multiple developmental processes via canonical signaling while revealing noncanonical activities. Recent data from both FGFRs and other RTKs highlight potential noncanonical roles in cell adhesion and nuclear signaling. The data supporting such functions are discussed as are recent technologies that have the potential to provide valuable insight into the developmental significance of these noncanonical activities.

L-Tryptophan activates the aryl hydrocarbon receptor and induces cell cycle arrest in porcine trophectoderm cells

During implantation, the proliferation of trophectoderm cells (the outer epithelium of blastocysts) is related to conceptus elongation and placenta formation. Tryptophan (Trp) is a key regulator of embryogenesis and embryonic implantation during pregnancy. We sought to determine whether different concentrations of Trp alters porcine trophectoderm (pTr) cell proliferation. pTr cells were cultured in medium containing 40, 500, or 1000 μM Trp. The cell proliferation rate and the progression of the cells through the cell cycle were determined. To identify differentially expressed genes (DEGs) in the pTr cells, we compared mRNA transcriptomes by RNA-Seq after cell treatment with different concentrations of Trp. Some candidate DEGs were identified by quantitative reverse transcription PCR (qPCR). High L-Trp levels (500 and 1000 μM) inhibited cell proliferation and induced cell cycle arrest. We identified 19 DEGs between the 500 μM L-Trp and 40 μM L-Trp groups and 168 DEGs between the 1000 μM L-Trp and 40 μM L-Trp groups and subsequently used qPCR to validate some genes that were upregulated or downregulated. The functional gene networks in which the DEGs were most enriched included those associated with regulating DNA replication and the cell cycle, and the majority of the DEGs in both of these functional pathways was downregulated. The results showed that the addition of 500 and 1000 μM Trp significantly increased the abundance of proteins in the Aryl Hydrocarbon Receptor (AHR) signaling pathway. Collectively, these results indicate a novel and important role for Trp in mediating the proliferation of porcine placental cells largely via the AHR signaling pathway. Additionally, these findings help to explain the side effects of excessive Trp supplementation on placenta development and embryo growth in mammals.

Self-organized signaling in stem cell models of embryos

Mammalian embryonic development is a complex process driven by self-organization. Understanding how a fertilized egg develops into an embryo composed of more than 200 cell types in precise spatial patterns remains one of the fundamental challenges in biology. Pluripotent stem cells have been used as in vitro models for investigating mammalian development, and represent promising building blocks for regenerative therapies. Recently, sophisticated stem cell-based models that recapitulate early embryonic fate patterning and morphogenesis have been developed. In this article, we review recent advances in stem cell models of embryos in particular focusing on signaling activities underpinning cell fate decisions in space and time.

Pluripotent stem cells in the research for extraembryonic cell differentiation

Mouse embryonic stem cells (mESCs) are pluripotent stem cell populations derived from the preimplantation embryo and are used to study the differentiation of many types of somatic and germ cells in developing embryos. They are also used to study cell lineages of extraembryonic tissues, such as the trophectoderm (TE) and the primitive endoderm (PrE). mESC cultures are suitable systems for reproducing cellular and molecular events occurring during the differentiation of these cell types, such as changes in gene expression patterns, signaling events, and genome rearrangements although the consistency between the results obtained using mESCs and those of in vivo studies on embryos should be carefully taken into account. Since TE and PrE cells can be induced from mESCs in vitro, mESC cultures are useful systems to study differentiation of these cell lineages during development, if used appropriately. In addition, human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), are capable of generating extraembryonic lineages in vitro and are promising tools to study the differentiation of these lineages in the human embryo.

Histone chaperone APLF level dictates the implantation of mouse embryos

Our recent findings demonstrated that the histone chaperone and DNA repair factor aprataxin and PNK-like factor (APLF) could regulate epithelial to mesenchymal transition (EMT) during the reprogramming of murine fibroblasts and in breast cancer metastasis. Therefore, we investigated the function of APLF in EMT associated with mouse development. Here, we show that APLF is predominantly enhanced in trophectoderm (TE) and lineages derived from TE in pre- and post-implantation embryos. Downregulation of APLF induced the hatching of embryos in vitro, with a significant increase in Cdh1 and Cdx2 expression. Aplf short hairpin RNA-microinjected embryos failed to implant in vivo Rescue experiments neutralized the knockdown effects of APLF both in vitro and in vivo Reduced expression of Snai2 and Tead4, and the gain in Cdh1 and sFlt1 (also known as Flt1) level, marked the differentiation of APLF-knocked down trophoblast stem cells that might contribute towards the impaired implantation of embryos. Hence, our findings suggest a novel role for APLF during implantation and post-implantation development of mouse embryos. We anticipate that APLF might contribute to the establishment of maternal-fetal connection, as its fine balance is required to achieve implantation and thereby attain proper pregnancy.

FGF signaling regulates development by processes beyond canonical pathways

FGFs are key developmental regulators that engage a signal transduction cascade through receptor tyrosine kinases, prominently engaging ERK1/2 but also other pathways. However, it remains unknown whether all FGF activities depend on this canonical signal transduction cascade. To address this question, we generated allelic series of knock-in Fgfr1 and Fgfr2 mouse strains, carrying point mutations that disrupt binding of signaling effectors, and a kinase dead allele of Fgfr2 that broadly phenocopies the null mutant. When interrogated in cranial neural crest cells, we identified discrete functions for signaling pathways in specific craniofacial contexts, but point mutations, even when combined, failed to recapitulate the single or double null mutant phenotypes. Furthermore, the signaling mutations abrogated established FGF-induced signal transduction pathways, yet FGF functions such as cell-matrix and cell-cell adhesion remained unaffected, though these activities did require FGFR kinase activity. Our studies establish combinatorial roles of Fgfr1 and Fgfr2 in development and uncouple novel FGFR kinase-dependent cell adhesion properties from canonical intracellular signaling.

Live Visualization of ERK Activity in the Mouse Blastocyst Reveals Lineage-Specific Signaling Dynamics

FGF/ERK signaling is crucial for the patterning and proliferation of cell lineages that comprise the mouse blastocyst. However, ERK signaling dynamics have never been directly visualized in live embryos. To address whether differential signaling is associated with particular cell fates and states, we generated a targeted mouse line expressing an ERK-kinase translocation reporter (KTR) that enables live quantification of ERK activity at single-cell resolution. 3D time-lapse imaging of this biosensor in embryos revealed spatially graded ERK activity in the trophectoderm prior to overt polar versus mural differentiation. Within the inner cell mass (ICM), all cells relayed FGF/ERK signals with varying durations and magnitude. Primitive endoderm cells displayed higher overall levels of ERK activity, while pluripotent epiblast cells exhibited lower basal activity with sporadic pulses. These results constitute a direct visualization of signaling events during mammalian pre-implantation development and reveal the existence of spatial and temporal lineage-specific dynamics.

Etv5 safeguards trophoblast stem cells differentiation from mouse EPSCs by regulating fibroblast growth factor receptor 2

Previous studies have demonstrated that transcription factor Etv5 plays an important role in the segregation between epiblast and primitive endoderm at the second fate decision of early embryo. However, it remains elusive whether Etv5 functions in the segregation between inner cell mass and trophectoderm at the first cell fate decision. In this study, we firstly generated Etv5 knockout mouse embryonic stem cells (mESCs) by CRISPR/Cas9, then converted them into extended potential stem cells (EPSCs) by culturing the cells in small molecule cocktail medium LCDM (LIF, CHIR99021, (S)-(+)-dimethindene maleate, minocycline hydrochloride), and finally investigated their differentiation efficiency of trophoblast stem cells (TSCs). The results showed that Etv5 knockout significantly decreased the efficiency of TSCs (CDX2⁺) differentiated from EPSCs. In addition, Etv5 knockout resulted in higher incidence of the differentiated cells with tetraploid and octoploid than that from wild type. Mechanistically, Etv5 was activated by extracellular-signal-regulated kinase (ERK) signaling pathway; in turn, Etv5 had a positive feedback on the expression of fibroblast growth factor receptor 2 (FGFR2) which lies upstream of ERK. Etv5 knockout decreased the expression of FGFR2, whose binding with fibroblast growth factor 4 was essentially needed for TSCs differentiation. Collectively, the findings in this study suggest that Etv5 is required to safeguard the TSCs differentiation by regulating FGFR2 and provide new clues to understand the specification of trophectoderm in vivo.

In vitro fertilization and embryo transfer alter human placental function through trophoblasts in early pregnancy

The mechanism underlying the potential risk associated with in vitro fertilization and embryo transfer (IVF‑ET) has been previously investigated but remains to be fully elucidated. As the placenta is a critical organ that sustains and protects the fetus, this is an important area of research. The aim of the present study was to determine the difference in trophoblast cell function in the first trimester between naturally conceived pregnancies and pregnancies achieved via IVF‑ET therapy. A total of 20 placental villi in first trimester samples were obtained through fetal bud aspiration from patients undergoing IVF‑ET due to oviductal factors between January 2016 and August 2018. In addition, a further 20 placental villi were obtained from those who naturally conceived and had normal pregnancies but were undergoing artificial abortion; these patients were recruited as the controls. Reverse transcription‑quantitative (RT‑q)PCR and semi‑quantitative immunohistochemical methods were used to detect the mRNA and protein expression of α‑fetoprotein (AFP), vascular endothelial growth factor (VEGF), transferrin (TF), tubulin β1 class VI (TUBB1), metallothionein 1G (MT1G), BCL2, glial cells missing transcription factor 1 (GCM1), epidermal growth factor (EGF) receptor (EGFR), PTEN and leukocyte associated immunoglobulin like receptor 2 (LAIR2) in villi from both groups. Differentially expressed genes were analyzed using Search Tool for the Retrieval of Interacting Genes, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted. The RT‑qPCR data revealed that the mRNA expression levels of AFP, VEGF and TF were significantly higher in the IVF‑ET group than in the control group (P<0.05), and those of TUBB1, MT1G, BCL2, GCM1, EGFR, PTEN and LAIR2 were significantly lower (P<0.05). These gene products were expressed in the placental villus tissues, either in the cytoplasm, or in the membrane of syncytiotrophoblast and cytotrophoblast cells. The immunohistochemistry results were in line with those observed using RT‑qPCR. KEGG pathway analysis indicated that the trophoblast cell function of the IVF‑ET group in the first trimester was different from naturally conceived pregnancies with regard to proliferation, invasion, apoptosis and vascular development. The IVF‑ET process may trigger adaptive placental responses, and these compensatory mechanisms could be a risk for certain diseases later in life.

Clinical Characteristics and Spermatogenesis in Patients with Congenital Hypogonadotropic Hypogonadism Caused by FGFR1 Mutations

OBJECTIVE

The aim of this study was to investigate the clinical characteristics of patients diagnosed with congenital hypogonadotropic hypogonadism (CHH) caused by FGFR1 (fibroblast growth factor receptor 1) gene mutations and to evaluate the effect of gonadotropin or pulsatile gonadotropin-releasing hormone (GnRH) therapy on spermatogenesis.

METHODS

A retrospective study was conducted on CHH patients admitted to Peking Union Medical College Hospital from January 2012 to March 2020. Clinical features and laboratory results were recorded. Testicular volume and sperm count responding to gonadotropin and pulsatile GnRH therapy were compared between the FGFR1 mutation group and the mutation-negative group.

RESULTS

(1) FGFR1 mutation group included 14 patients who received sperm-induction therapy, and the mutation-negative group enrolled 25 CHH patients. (2) The incidence of cryptorchidism was 50.0% (7/14) and 12.0% (3/25) in the FGFR1 group and the mutation-negative group, respectively (p=0.019). The baseline testicular volume of the FGFR1 mutation group was smaller than that of the mutation-negative group, 1.6 (0.5-2.0) mL vs. 2 (1.75-4) mL (p=0.033). The baseline luteinizing hormone (LH), Follicle-stimulating hormone (FSH), and testosterone levels were similar between the two groups. (3) Using the Kaplan-Meier and log-rank tests for the analysis of spermatogenesis, it was found that there was no significant difference in the first sperm appearance between the FGFR1 mutation group and the mutation-negative group (χ ² = 1.974, p=0.160). The median time of spermatogenesis in the FGFR1 mutation group was longer than that in the mutation-negative group, 16 months vs. 10 months, respectively. The cumulative spermatogenesis success rate at 12 months in the FGFR1 mutation group (35.71%) was lower than that in the mutation-negative group (68.75%) (p=0.047). The sperm concentration in the mutation-negative group was more easily achieved for different thresholds compared with that in the FGFR1 mutation group, but no significant difference was observed (p > 0.05) between the two groups. The last follow-up examination showed that the testicular volume was 7.00 (4.75-12.00) mL and 10.56 ± 4.82 mL (p=0.098), the ejaculate volume of sperm was 2.20 (1.40-2.26) mL and 3.06 ± 1.42 mL (p=0.175), and the sperm concentration was 7.19 (1.00-9.91) million/mL and 18.80 (4.58-53.62) million/mL (p=0.038) in the FGFR1 mutation and mutation-negative groups, respectively, while the sperm motility (A%, A + B%, and A + B + C%) was similar for the two groups (p=0.839, 0.909, and 0.759, respectively). The testosterone level during treatment was 366.02 ± 167.03 ng/dL and 362.27 ± 212.86 ng/dL in the FGFR1 mutation and mutation-negative groups, respectively (p=0.956).

CONCLUSION

Patients with FGFR1 mutations have a higher prevalence of cryptorchidism and smaller testicular volume. Although patients with FGFR1 mutations have a similar rate of success for spermatogenesis compared to that of the mutation-negative patients, a longer treatment period was required and a lower sperm concentration was achieved.

Genome-wide assessment of DNA methylation in mouse oocytes reveals effects associated with in vitro growth, superovulation, and sexual maturity

Background

In vitro follicle culture (IFC), as applied in the mouse system, allows the growth and maturation of a large number of immature preantral follicles to become mature and competent oocytes. In the human oncofertility clinic, there is increasing interest in developing this technique as an alternative to ovarian cortical tissue transplantation and to preserve the fertility of prepubertal cancer patients. However, the effect of IFC and hormonal stimulation on DNA methylation in the oocyte is not fully known, and there is legitimate concern over epigenetic abnormalities that could be induced by procedures applied during assisted reproductive technology (ART).

Results

In this study, we present the first genome-wide analysis of DNA methylation in MII oocytes obtained after natural ovulation, after IFC and after superovulation. We also performed a comparison between prepubertal and adult hormonally stimulated oocytes. Globally, the distinctive methylation landscape of oocytes, comprising alternating hyper- and hypomethylated domains, is preserved irrespective of the procedure. The conservation of methylation extends to the germline differential methylated regions (DMRs) of imprinted genes, necessary for their monoallelic expression in the embryo. However, we do detect specific, consistent, and coherent differences in DNA methylation in IFC oocytes, and between oocytes obtained after superovulation from prepubertal compared with sexually mature females. Several methylation differences span entire transcription units. Among these, we found alterations in Tcf4, Sox5, Zfp521, and other genes related to nervous system development.

Conclusions

Our observations show that IFC is associated with altered methylation at specific set of loci. DNA methylation of superovulated prepubertal oocytes differs from that of superovulated adult oocytes, whereas oocytes from superovulated adult females differ very little from naturally ovulated oocytes. Importantly, we show that regions other than imprinted gDMRs are susceptible to methylation changes associated with superovulation, IFC, and/or sexual immaturity in mouse oocytes. Our results provide an important reference for the use of in vitro growth and maturation of oocytes, particularly from prepubertal females, in assisted reproductive treatments or fertility preservation.

Trophectoderm regeneration to support full-term development in the inner cell mass isolated from bovine blastocyst

Which comes first: tissue structure or cell differentiation? Although different cell types establish distinct structures delineating the inside and outside of an embryo, they progressively become specified by the blastocyst stage, when two types of cell lineages are formed: the inner cell mass (ICM) and the trophectoderm (TE). This inside-outside aspect can be experimentally converted by the isolation of the ICM from a blastocyst, leading to a posteriori externalization of the blastomeres composing the outermost layer of the ICM. Here, we investigated the totipotency of isolated mouse and bovine ICMs to determine whether they are competent for TE regeneration. Surprisingly, a calf was generated from the bovine isolated ICM with re-formed blastocoel (re-iICM), but no mouse re-iICMs developed to term. To further explore the cause of difference in developmental competency between the mouse and bovine re-iICMs, we investigated the SOX17 protein expression that is a representative molecular marker of primitive endoderm. The localization pattern of SOX17 was totally different between mouse and bovine embryos. Particularly, the ectopic SOX17 localization in the TE might be associated with lethality of mouse re-iICMs. Meanwhile, transcriptome sequencing revealed that some of the bovine re-iICMs showed transcriptional patterns of TE-specific genes similar to those of whole blastocysts. Our findings suggest that TE regeneration competency is maintained longer in bovine ICMs than in mouse ICMs and provide evidence that the ICM/TE cell fate decision is influenced by structural determinants, including positional information of each blastomere in mammalian embryos.

The placental transcriptome of the first-trimester placenta is affected by in vitro fertilization and embryo transfer

BACKGROUND

The placenta is a highly specialized temporary organ that is related to fetal development and pregnancy outcomes, and epidemiological data demonstrate an increased risk of placental abnormality after in vitro fertilization and embryo transfer (IVF-ET).

METHODS

This study examines alterations in the transcriptome profile of first-trimester placentas from IVF-ET pregnancies and analyzes the potential mechanisms that play a role in the adverse perinatal outcomes associated with IVF-ET procedures. Four human placental villi from first-trimester samples were obtained through fetal bud aspiration from patients subjected to IVF-ET due to oviductal factors. An additional four control human placental villi were derived from a group of subjects who spontaneously conceived a twin pregnancy. We analyzed their transcriptomes by microarray. Then, RT-qPCR and immunohistochemistry were utilized to analyze several dysregulated genes to validate the microarray results. Biological functions and pathways were analyzed with bioinformatics tools.

RESULTS

A total of 3405 differentially regulated genes were identified as significantly dysregulated (> 2-fold change; P < 0.05) in the IVF-ET placenta in the first trimester: 1910 upregulated and 1495 downregulated genes. Functional enrichment analysis of the differentially regulated genes demonstrated that the genes were involved in more than 50 biological processes and pathways that have been shown to play important roles in the first trimester in vivo. These pathways can be clustered into coagulation cascades, immune response, transmembrane signaling, metabolism, cell cycle, stress control, invasion and vascularization. Nearly the same number of up- and downregulated genes participate in the same biological processes related to placental development and maintenance. Procedures utilized in IVF-ET altered the expression of first-trimester placental genes that are critical to these biological processes and triggered a compensatory mechanism during early implantation in vivo.

CONCLUSION

These data provide a potential basis for further analysis of the higher frequency of adverse perinatal outcomes following IVF-ET, with the ultimate goal of developing safer IVF-ET protocols.