Binding of FGF2 to FGFR2 in an autocrine mode in trophectoderm cells is indispensable for mouse blastocyst formation through PKC-p38 pathway

Influence of FGF4 and BMP4 on FGFR2 dynamics during the segregation of epiblast and primitive endoderm cells in the pre-implantation mouse embryo

Specification of the epiblast (EPI) and primitive endoderm (PE) in the mouse embryo involves fibroblast growth factor (FGF) signaling through the RAS/MAP kinase pathway. FGFR1 and FGFR2 are thought to mediate this signaling in the inner cell mass (ICM) of the mouse blastocyst and BMP signaling can also influence PE specification. In this study, we further explored the dynamics of FGFR2 expression through an enhanced green fluorescent protein (eGFP) reporter mouse line (FGFR2-eGFP). We observed that FGFR2-eGFP is present in the late 8-cell stage; however, it is absent or reduced in the ICM of early blastocysts. We then statistically correlated eGFP expression with PE and EPI markers GATA6 and NANOG, respectively. We detected that eGFP is weakly correlated with GATA6 in early blastocysts, but this correlation quickly increases as the blastocyst develops. The correlation between eGFP and NANOG decreases throughout blastocyst development. Treatment with FGF from the morula stage onwards did not affect FGFR2-eGFP presence in the ICM of early blastocysts; however, late blastocysts presented FGFR2-eGFP in all cells of the ICM. BMP treatment positively influenced FGFR2-eGFP expression and reduced the number of NANOG-positive cells in late blastocysts. In conclusion, FGFR2 is not strongly associated with PE precursors in the early blastocyst, but it is highly correlated with PE cells as blastocyst development progresses, consistent with the proposed role for FGFR2 in maintenance rather than initiating the PE lineage.

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.

An investigation of mechanisms underlying mouse blastocyst hatching: a ribonucleic acid sequencing study

OBJECTIVE

To investigate the regulatory mechanisms and signaling molecules underlying hatching in mouse embryos.

DESIGN

Experimental laboratory study using a mouse embryo model.

SETTING

University-based basic scientific research laboratory.

ANIMALS

A total of 40 B6C3F1 × B6D2F1 mouse embryos were used in this study.

INTERVENTION(S)

Frozen/thawed mouse embryos, at the 8-cell stage, were cultured in vitro for 2 days. The resulting hatching and prehatching blastocysts were then used for complementary deoxyribonucleic acid (cDNA) library preparation and ribonucleic acid (RNA) sequencing analysis (n = 8 for each group). Differentially expressed genes were then used for downstream functional analysis. In addition, a list of genes related to developmental progression in humans was used to identify genes that were potentially related to the hatching of human embryos.

MAIN OUTCOME MEASURE(S)

Differentially expressed genes, enriched Gene Ontology terms and canonical pathways, clustered gene networks, activated upstream regulators, and common genes between a gene list of hatching-related genes in mice and a gene list associated with developmental progression in humans.

RESULT(S)

A total 275 differentially expressed genes were identified between hatching and prehatching blastocysts: 230 up-regulated and 45 down-regulated genes. Functional enrichment analysis suggested that blastocyst hatching in vitro is an adenosine triphosphate (ATP)-dependent process that involves protein biosynthesis and organization of the cytoskeleton. Furthermore, by regulating cell motility, the RhoA signaling pathway (including Arpc2, Cfl1, Gsn, Pfn1, Tpi1, Grb2, Tmsb10, Enah, and Rnd3 genes) may be a crucial signaling pathway during hatching. We also identified a cluster of genes (Krt8, Krt7, Cldn4, and Aqp3) that exerted functional roles in cell-cell junctions and water homeostasis during hatching. Moreover, some growth factors (angiotensinogen and fibroblast growth factor 2) and endocrine factors (estrogen receptor and prolactin) were predicted to be involved in the regulation of embryo hatching. In addition, we identified 81 potential genes that are potentially involved in the hatching process in human embryos.

CONCLUSION(S)

Our analysis identified potential genes and molecular regulatory pathways involved in the blastocyst hatching process in mice; we also identified genes that may potentially regulate hatching in human embryos. Our findings enhance our knowledge of embryo development and provide useful information for further exploring the mechanisms underlying embryo hatching.

p38-MAPK-mediated translation regulation during early blastocyst development is required for primitive endoderm differentiation in mice

Successful specification of the two mouse blastocyst inner cell mass (ICM) lineages (the primitive endoderm (PrE) and epiblast) is a prerequisite for continued development and requires active fibroblast growth factor 4 (FGF4) signaling. Previously, we identified a role for p38 mitogen-activated protein kinases (p38-MAPKs) during PrE differentiation, but the underlying mechanisms have remained unresolved. Here, we report an early blastocyst window of p38-MAPK activity that is required to regulate ribosome-related gene expression, rRNA precursor processing, polysome formation and protein translation. We show that p38-MAPK inhibition-induced PrE phenotypes can be partially rescued by activating the translational regulator mTOR. However, similar PrE phenotypes associated with extracellular signal-regulated kinase (ERK) pathway inhibition targeting active FGF4 signaling are not affected by mTOR activation. These data indicate a specific role for p38-MAPKs in providing a permissive translational environment during mouse blastocyst PrE differentiation that is distinct from classically reported FGF4-based mechanisms.

Expression Analysis of FGF/FGFR and FOX Family Proteins in Mucosal Tissue Obtained from Orofacial Cleft-Affected Children

Orofacial clefts affect hundreds of thousands of children worldwide annually and are usually corrected by a series of surgeries extending to childhood. The underlying mechanisms that lead to clefts are still unknown, mainly because of the multifactorial etiology and the myriad of interactions between genes and environmental factors. In the present study, we investigated the role and expression of candidate genes belonging to the FGF/FGFR signaling pathway and FOX family in tissue material obtained from 12 pediatric patients undergoing cleft correction surgery. The expression was investigated using immunohistochemistry (IHC) and chromogenic in-situ hybridization (CISH) in three cell/tissue types-epithelial cells, connective tissue, and endothelial cells. We found elevated expression of FGFR1 in epithelial cells while no expression was observed in endothelial cells. Further, our results elucidate the potential pathogenetic role of FGFR1 in cellular proliferation, local site inflammation, and fibrosis in cleft patients. Along with bFGF (also called FGF2), FGFR1 could play a pro-inflammatory role in clefts. Over-amplification of FGFR2 in some patients, along with bFGF, could potentially suggest roles for these genes in angiogenesis. Additionally, increased expression of FOXE1 (also called TTF2) contributes to local site inflammation. Finally, zero to low amplification of FOXO1 could suggest its potential role in inducing oxidative stress in the endothelium along with reduced epithelial apoptosis.

Oxidative stress-induced TGF-beta/TAB1-mediated p38MAPK activation in human amnion epithelial cells

Term and preterm parturition are associated with oxidative stress (OS)-induced p38 mitogen-activated protein kinase (p38MAPK)-mediated fetal tissue (amniochorion) senescence. p38MAPK activation is a complex cell- and stimulant-dependent process. Two independent pathways of OS-induced p38MAPK activation were investigated in amnion epithelial cells (AECs) in response to cigarette smoke extract (CSE: a validated OS inducer in fetal cells): (1) the OS-mediated oxidation of apoptosis signal-regulating kinase (ASK)-1 bound Thioredoxin (Trx[SH]2) dissociates this complex, creating free and activated ASK1-signalosome and (2) transforming growth factor-mediated activation of (TGF)-beta-activated kinase (TAK)1 and TGF-beta-activated kinase 1-binding protein (TAB)1. AECs isolated from normal term, not-in-labor fetal membranes increased p38MAPK in response to CSE and downregulated it in response to antioxidant N-acetylcysteine. In AECs, both Trx and ASK1 were localized; however, they remained dissociated and not complexed, regardless of conditions. Silencing either ASK1 or its downstream effectors (MKK3/6) did not affect OS-induced p38MAPK activation. Conversely, OS increased TGF-beta's release from AECs and increased phosphorylation of both p38MAPK and TAB1. Silencing of TAB1, but not TAK1, prevented p38MAPK activation, which is indicative of TAB1-mediated autophosphorylation of p38MAPK, an activation mechanism seldom seen. OS-induced p38MAPK activation in AECs is ASK1-Trx signalosome-independent and is mediated by the TGF-beta pathway. This knowledge will help to design strategies to reduce p38MAPK activation-associated pregnancy risks.

Plasticity of the inner cell mass in mouse blastocyst is restricted by the activity of FGF/MAPK pathway

In order to ensure successful development, cells of the early mammalian embryo must differentiate to either trophectoderm (TE) or inner cell mass (ICM), followed by epiblast (EPI) or primitive endoderm (PE) specification within the ICM. Here, we deciphered the mechanism that assures the correct order of these sequential cell fate decisions. We revealed that TE-deprived ICMs derived from 32-cell blastocysts are still able to reconstruct TE during in vitro culture, confirming totipotency of ICM cells at this stage. ICMs isolated from more advanced blastocysts no longer retain totipotency, failing to form TE and generating PE on their surface. We demonstrated that the transition from full potency to lineage priming is prevented by inhibition of the FGF/MAPK signalling pathway. Moreover, we found that after this first restriction step, ICM cells still retain fate flexibility, manifested by ability to convert their fate into an alternative lineage (PE towards EPI and vice versa), until peri-implantation stage.

Gabapentin regulates expression of FGF2 and FGFR1 in dorsal root ganglia via microRNA-15a in the arthritis rat model

BACKGROUND

Arthritis is an inflammatory disease with a prevalence rate of approximately 10% in China, which commonly manifests as pain. The aim of the current study was to investigate the function of gabapentin in the dorsal root ganglion in an arthritis rat model, and assess the effect of gabapentin on the expression of fibroblast growth factor 2 (FGF2) and FGF receptor 1 (FGFR1).

METHODS

A total of 30 healthy male Sprague-Dawley rats were randomly divided into the following three groups: Untreated group, control group and gabapentin group. Rats in the control and the gabapentin groups were injected with Freund's complete adjuvant to induce arthritis. A total of 7 days subsequent to model establishment, the gabapentin group was administered intraperitoneally gabapentin for 8 days. The alterations in thickness of paw pad and paw withdrawal mechanical threshold (PWMT) were detected, which indicated that the rats in the control and gabapentin groups presented with the symptoms of arthritis.

RESULTS

In the control group, the PWMT value was significantly reduced (P < 0.05), whereas the PWMT value was significantly increased in the gabapentin group. Immunohistochemistry demonstrated that the expression levels of FGF2 and FGFR1 were increased in the control group compared with the untreated group, while the expression levels of FGF2 and FGFR1 were reduced in the gabapentin group. Moreover, the FGF2 antagonist PD173074 partially improved the plantar thickness and PWMT of the arthritic rats. Bioinformatics analysis predicted microRNA-15a binding sites in the 3'untranslated regions (UTR) of FGF2 and FGFR1. Furthermore, the expression of microRNA-15a was reduced in the control group compared with untreated rats, whereas microRNA-15a in the gabapentin group was upregulated compared with the control. Additionally, the luciferase reporter assay confirmed that microRNA-15a could inhibit the protein expression through pairing with the 3'UTR of FGF2 and FGFR1 mRNAs.

CONCLUSION

Gabapentin may relieve arthritis pain and reduce the expression of FGF2 and FGFR1 in dorsal root ganglia. Furthermore, microRNA-15a may be involved in the regulatory process.

p38 (Mapk14/11) occupies a regulatory node governing entry into primitive endoderm differentiation during preimplantation mouse embryo development

During mouse preimplantation embryo development, the classically described second cell-fate decision involves the specification and segregation, in blastocyst inner cell mass (ICM), of primitive endoderm (PrE) from pluripotent epiblast (EPI). The active role of fibroblast growth factor (Fgf) signalling during PrE differentiation, particularly in the context of Erk1/2 pathway activation, is well described. However, we report that p38 family mitogen-activated protein kinases (namely p38α/Mapk14 and p38β/Mapk11; referred to as p38-Mapk14/11) also participate in PrE formation. Specifically, functional p38-Mapk14/11 are required, during early-blastocyst maturation, to assist uncommitted ICM cells, expressing both EPI and earlier PrE markers, to fully commit to PrE differentiation. Moreover, functional activation of p38-Mapk14/11 is, as reported for Erk1/2, under the control of Fgf-receptor signalling, plus active Tak1 kinase (involved in non-canonical bone morphogenetic protein (Bmp)-receptor-mediated PrE differentiation). However, we demonstrate that the critical window of p38-Mapk14/11 activation precedes the E3.75 timepoint (defined by the initiation of the classical ‘salt and pepper’ expression pattern of mutually exclusive EPI and PrE markers), whereas appropriate lineage maturation is still achievable when Erk1/2 activity (via Mek1/2 inhibition) is limited to a period after E3.75. We propose that active p38-Mapk14/11 act as enablers, and Erk1/2 as drivers, of PrE differentiation during ICM lineage specification and segregation.

The formation of multivesicular bodies in activated blastocysts is influenced by autophagy and FGF signaling in mice

Dormant blastocysts during delayed implantation undergo autophagic activation, which is an adaptive response to prolonged survival in utero during less favorable environment. We observed that multivesicular bodies (MVBs) accumulate in the trophectoderm of dormant blastocysts upon activation for implantation. Since autophagosomes are shown to fuse with MVBs and efficient autophagic degradation requires functional MVBs, we examined if MVB formation in activated blastocysts are associated with protracted autophagic state during dormancy. We show here that autophagic activation during dormancy is one precondition for MVB formation in activated blastocysts. Furthermore, the blockade of FGF signaling with PD173074 partially interferes with MVB formation in these blastocysts, suggesting the involvement of FGFR signaling in this process. We believe that MVB formation in activated blastocysts after dormancy is a potential mechanism of clearing subcellular debris accumulated during prolonged autophagy.