An essential function of the mitogen-activated protein kinase Erk2 in mouse trophoblast development

The ERK Pathway: Molecular Mechanisms and Treatment of Depression

Major depressive disorder is a chronic debilitating mental illness. Its pathophysiology at cellular and molecular levels is incompletely understood. Increasing evidence supports a pivotal role of the mitogen-activated protein kinase (MAPK), in particular the extracellular signal-regulated kinase (ERK) subclass of MAPKs, in the pathogenesis, symptomatology, and treatment of depression. In humans and various chronic animal models of depression, the ERK signaling was significantly downregulated in the prefrontal cortex and hippocampus, two core areas implicated in depression. Inhibiting the ERK pathway in these areas caused depression-like behavior. A variety of antidepressants produced their behavioral effects in part via normalizing the downregulated ERK activity. In addition to ERK, the brain-derived neurotrophic factor (BDNF), an immediate upstream regulator of ERK, the cAMP response element-binding protein (CREB), a transcription factor downstream to ERK, and the MAPK phosphatase (MKP) are equally vulnerable to depression. While BDNF and CREB were reduced in their activity in the prefrontal cortex and hippocampus of depressed animals, MKP activity was enhanced in parallel. Chronic antidepressant treatment readily reversed these neurochemical changes. Thus, ERK signaling in the depression-implicated brain regions was disrupted during the development of depression, which contributes to the long-lasting and transcription-dependent neuroadaptations critical for enduring depression-like behavior and the therapeutic effect of antidepressants.

FGFR1 regulates trophectoderm development and facilitates blastocyst implantation

FGF signaling plays important roles in many aspects of mammalian development. Fgfr1^-/- and Fgfr1^-/-Fgfr2^-/- mouse embryos on a 129S4 co-isogenic background fail to survive past the peri-implantation stage, whereas Fgfr2^-/- embryos die at midgestation and show defects in limb and placental development. To investigate the basis for the Fgfr1^-/- and Fgfr1^-/-Fgfr2^-/- peri-implantation lethality, we examined the role of FGFR1 and FGFR2 in trophectoderm (TE) development. In vivo, Fgfr1^-/- TE cells failed to downregulate CDX2 in the mural compartment and exhibited abnormal apicobasal E-Cadherin polarity. In vitro, we were able to derive mutant trophoblast stem cells (TSCs) from Fgfr1^-/- or Fgfr2^-/- single mutant, but not from Fgfr1^-/-Fgfr2^-/- double mutant blastocysts. Fgfr1^-/- TSCs however failed to efficiently upregulate TE differentiation markers upon differentiation. These results suggest that while the TE is specified in Fgfr1^-/- mutants, its differentiation abilities are compromised leading to defects at implantation.

MAPK and PI3K signaling: At the crossroads of neural crest development

Receptor tyrosine kinase-mediated growth factor signaling is essential for proper formation and development of the neural crest. The many ligands and receptors implicated in these processes signal through relatively few downstream pathways, frequently converging on the MAPK and PI3K pathways. Despite decades of study, there is still considerable uncertainty about where and when these signaling pathways are required and how they elicit particular responses. This review summarizes our current understanding of growth factor-induced MAPK and PI3K signaling in the neural crest.

ERK1/2 inhibitors: New weapons to inhibit the RAS-regulated RAF-MEK1/2-ERK1/2 pathway

The RAS-regulated RAF-MEK1/2-ERK1/2 signalling pathway is de-regulated in a variety of cancers due to mutations in receptor tyrosine kinases (RTKs), negative regulators of RAS (such as NF1) and core pathway components themselves (RAS, BRAF, CRAF, MEK1 or MEK2). This has driven the development of a variety of pharmaceutical agents to inhibit RAF-MEK1/2-ERK1/2 signalling in cancer and both RAF and MEK inhibitors are now approved and used in the clinic. There is now much interest in targeting at the level of ERK1/2 for a variety of reasons. First, since the pathway is linear from RAF-to-MEK-to-ERK then ERK1/2 are validated as targets per se. Second, innate resistance to RAF or MEK inhibitors involves relief of negative feedback and pathway re-activation with all signalling going through ERK1/2, validating the use of ERK inhibitors with RAF or MEK inhibitors as an up-front combination. Third, long-term acquired resistance to RAF or MEK inhibitors involves a variety of mechanisms (KRAS or BRAF amplification, MEK mutation, etc.) which re-instate ERK activity, validating the use of ERK inhibitors to forestall acquired resistance to RAF or MEK inhibitors. The first potent highly selective ERK1/2 inhibitors have now been developed and are entering clinical trials. They have one of three discrete mechanisms of action - catalytic, "dual mechanism" or covalent - which could have profound consequences for how cells respond and adapt. In this review we describe the validation of ERK1/2 as anti-cancer drug targets, consider the mechanism of action of new ERK1/2 inhibitors and how this may impact on their efficacy, anticipate factors that will determine how tumour cells respond and adapt to ERK1/2 inhibitors and consider ERK1/2 inhibitor drug combinations.

Circulating mRNA in Maternal Plasma at the Second Trimester of Pregnancy: A Possible Screening Tool for Cardiac Conotruncal and Left Ventricular Outflow Tract Abnormalities

OBJECTIVE

Maternal plasma is a source of circulating placental nucleic acids. This study was designed to detect aberrantly expressed placental mRNA genes circulating in the maternal plasma of pregnancies affected with fetal conotruncal anomalies (CNTRA) and left-ventricular outflow tract (LVOT) obstruction in the second trimester of pregnancy.

METHODS

This was a retrospective monocentric study conducted from 1 Jan 2016 to 31 Dec 2016. NanoString technology was used to identify aberrantly expressed genes, comparing 36 women carrying a fetus with CNTRA or LVOT obstruction to 42 controls at 19-24 weeks of gestation. The genes with differential expression were subsequently tested using real-time polymerase chain reaction. Linear discriminant analysis was used to combine all the mRNA species with discriminant ability for CNTRA and LVOT obstruction. A multivariable receiver operating characteristic (ROC) curve having the estimated discriminant score as an explanatory variable was generated for the two affected groups versus controls.

RESULTS

Three genes with differential expression, namely MAPK1, IQGAP1 and Visfatin were found. The ROC curves yielded detection rates of 60 and 62.5% at a false-positive rate of 5% for CNTRA and LVOT, respectively.

CONCLUSIONS

These data suggested that molecular screening of CNTRA and LVOT obstruction in the second trimester is feasible. Prospective studies are needed to test the discriminant ability of these genes and to calculate the predictive positive value in the general population.

Blastocyst-like structures generated solely from stem cells

The blastocyst (the early mammalian embryo) forms all embryonic and extra-embryonic tissues, including the placenta. It consists of a spherical thin-walled layer, known as the trophectoderm, that surrounds a fluid-filled cavity sheltering the embryonic cells ¹ . From mouse blastocysts, it is possible to derive both trophoblast ² and embryonic stem-cell lines ³ , which are in vitro analogues of the trophectoderm and embryonic compartments, respectively. Here we report that trophoblast and embryonic stem cells cooperate in vitro to form structures that morphologically and transcriptionally resemble embryonic day 3.5 blastocysts, termed blastoids. Like blastocysts, blastoids form from inductive signals that originate from the inner embryonic cells and drive the development of the outer trophectoderm. The nature and function of these signals have been largely unexplored. Genetically and physically uncoupling the embryonic and trophectoderm compartments, along with single-cell transcriptomics, reveals the extensive inventory of embryonic inductions. We specifically show that the embryonic cells maintain trophoblast proliferation and self-renewal, while fine-tuning trophoblast epithelial morphogenesis in part via a BMP4/Nodal-KLF6 axis. Although blastoids do not support the development of bona fide embryos, we demonstrate that embryonic inductions are crucial to form a trophectoderm state that robustly implants and triggers decidualization in utero. Thus, at this stage, the nascent embryo fuels trophectoderm development and implantation.

Impaired neuronal maturation of hippocampal neural progenitor cells in mice lacking CRAF

RAF kinases are major constituents of the mitogen activated signaling pathway, regulating cell proliferation, differentiation and cell survival of many cell types, including neurons. In mammals, the family of RAF proteins consists of three members, ARAF, BRAF, and CRAF. Ablation of CRAF kinase in inbred mouse strains causes major developmental defects during fetal growth and embryonic or perinatal lethality. Heterozygous germline mutations in CRAF result in Noonan syndrome, which is characterized by neurocognitive impairment that may involve hippocampal physiology. The role of CRAF signaling during hippocampal development and generation of new postnatal hippocampal granule neurons has not been examined and may provide novel insight into the cause of hippocampal dysfunction in Noonan syndrome. In this study, by crossing CRAF-deficiency to CD-1 outbred mice, a CRAF mouse model was established which enabled us to investigate the interplay of neural progenitor proliferation and postmitotic differentiation during adult neurogenesis in the hippocampus. Albeit the general morphology of the hippocampus was unchanged, CRAF-deficient mice displayed smaller granule cell layer (GCL) volume at postnatal day 30 (P30). In CRAF-deficient mice a substantial number of abnormal, chromophilic, fast dividing cells were found in the subgranular zone (SGZ) and hilus of the dentate gyrus (DG), indicating that CRAF signaling contributes to hippocampal neural progenitor proliferation. CRAF-deficient neural progenitor cells showed an increased cell death rate and reduced neuronal maturation. These results indicate that CRAF function affects postmitotic neural cell differentiation and points to a critical role of CRAF-dependent growth factor signaling pathway in the postmitotic development of adult-born neurons.

Isoform-selective activity-based profiling of ERK signaling

Extracellular signal-regulated kinases (ERKs) mediate downstream signaling of RAS-RAF-MEK as key regulators of the mitogen-activated protein kinase (MAPK) pathway. Activation of ERK signaling is a hallmark of cancer and upstream MAPK proteins have been extensively pursued as drug targets for cancer therapies. However, the rapid rise of resistance to clinical RAF and MEK inhibitors has prompted interest in targeting ERK (ERK1 and ERK2 isoforms) directly for cancer therapy. Current methods for evaluating activity of inhibitors against ERK isoforms are based primarily on analysis of recombinant proteins. Strategies to directly and independently profile native ERK1 and ERK2 activity would greatly complement current cell biological tools used to probe and target ERK function. Here, we present a quantitative chemoproteomic strategy that utilizes active-site directed probes to directly quantify native ERK activity in an isoform-specific fashion. We exploit a single isoleucine/leucine difference in ERK substrate binding sites to enable activity-based profiling of ERK1 versus ERK2 across a variety of cell types, tissues, and species. We used our chemoproteomic strategy to determine potency and selectivity of academic (VX-11e) and clinical (Ulixertinib) ERK inhibitors. Correlation of potency estimates by chemoproteomics with anti-proliferative activity of VX-11e and Ulixertinib revealed that >90% inactivation of both native ERK1 and ERK2 is needed to mediate cellular activity of inhibitors. Our findings introduce one of the first assays capable of independent evaluation of native ERK1 and ERK2 activity to advance drug discovery of oncogenic MAPK pathways.

Extracellular-Regulated Kinases: Signaling From Ras to ERK Substrates to Control Biological Outcomes

The extracellular-regulated kinases ERK1 and ERK2 are evolutionarily conserved, ubiquitous serine-threonine kinases that are involved in regulating cellular signaling in both normal and pathological conditions. Their expression is critical for development and their hyperactivation is a major factor in cancer development and progression. Since their discovery as one of the major signaling mediators activated by mitogens and Ras mutation, we have learned much about their regulation, including their activation, binding partners and substrates. In this review I will discuss some of what has been discovered about the members of the Ras to ERK pathway, including regulation of their activation by growth factors and cell adhesion pathways. Looking downstream of ERK activation I will also highlight some of the many ERK substrates that have been discovered, including those involved in feedback regulation, cell migration and cell cycle progression through the control of transcription, pre-mRNA splicing and protein synthesis.

Sex- and Age-Specific Impact of ERK Loss Within the Pituitary Gonadotrope in Mice

Extracellular signal-regulated kinase (ERK) signaling regulates hormone action in the reproductive axis, but specific mechanisms have yet to be completely elucidated. In the current study, ERK1 null and ERK2 floxed mice were combined with a gonadotropin-releasing hormone receptor (GnRHR)-internal ribosomal entry site-Cre (GRIC) driver. Female ERK double-knockout (ERKdko) animals were hypogonadotropic, resulting in anovulation and complete infertility. Transcript levels of four gonadotrope-specific genes (GnRHR and the three gonadotropin subunits) were reduced in pituitaries at estrus in ERKdko females, and the postcastration response to endogenous GnRH hyperstimulation was blunted. As females aged, they exhibited abnormal ovarian histology, as well as increased body weight. ERKdko males were initially less affected, showing moderate subfertility, up to 6 months of age. Male ERKdko mice also displayed a blunted response to endogenous GnRH following castration. By 12 months of age, ERKdko males had reduced testicular weights and sperm production. By 18 months of age, the ERKdko males displayed reduced testis and seminal vesicle weights, marked seminiferous tubule degeneration, and a 77% reduction in sperm production relative to controls. As the GRIC is also active in the male germ line, we examined the specific role of ERK loss in the testes using the stimulated by retinoic acid 8 (Stra8)-Cre driver. Whereas ERK loss in GRIC and Stra8 males resulted in comparable losses in sperm production, seminiferous tubule histological degeneration was only observed in the GRIC-ERKdko animals. Our data suggest that loss of ERK signaling and hypogonadotropism within the reproductive axis impacts fertility and gonadal aging.

Kidney-Replenishing Herb Induces SOCS-3 Expression via ERK/MAPK Pathway and Improves Growth of the First-Trimester Human Trophoblast Cells

Kidney-replenishing herb is a traditional medicine formula in China which has been widely used for clinical treatment of recurrent miscarriage. Our previous study showed that Kidney-replenishing herb could promote proliferation and inhibit apoptosis of the human first-trimester trophoblasts. In the present study, we further explored the potential mechanism and signal pathway of Kidney-replenishing herb on human trophoblast cells. Our research showed that Kidney-replenishing herb stimulated proliferation and reduced apoptosis of human trophoblast cells in vitro, and this appeared to be positive correlation with SOCS-3 transcription, suggesting that Kidney-replenishing herb regulated biological functions of human trophoblast cells by inducing SCOS-3 expression. Furthermore, the Kidney-replenishing herb treatment stimulated the phosphorylation of ERK1/2, and blocking the signaling pathway by mitogen-activated protein MAPK (MEK) inhibitor, U0126, inhibited Kidney-replenishing herb-induced SOCS-3 transcription, depressed proliferation, and promoted apoptosis of human trophoblasts. Kidney-replenishing herbs still induced ERK1/2 phosphorylation after SOCS-3 siRNA silence. Overexpression of SOCS-3 stimulated the proliferation of trophoblast. These findings suggest that SOCS-3 expression is induced by Kidney-replenishing herbs via activation of MAPK pathways, and this may possibly be involved in promoting human trophoblast cells growth which is contributed to embryo development.

Establishment of mouse expanded potential stem cells

Mouse embryonic stem cells derived from the epiblast contribute to the somatic lineages and the germline but are excluded from the extra-embryonic tissues that are derived from the trophectoderm and the primitive endoderm upon reintroduction to the blastocyst. Here we report that cultures of expanded potential stem cells can be established from individual eight-cell blastomeres, and by direct conversion of mouse embryonic stem cells and induced pluripotent stem cells. Remarkably, a single expanded potential stem cell can contribute both to the embryo proper and to the trophectoderm lineages in a chimaera assay. Bona fide trophoblast stem cell lines and extra-embryonic endoderm stem cells can be directly derived from expanded potential stem cells in vitro. Molecular analyses of the epigenome and single-cell transcriptome reveal enrichment for blastomere-specific signature and a dynamic DNA methylome in expanded potential stem cells. The generation of mouse expanded potential stem cells highlights the feasibility of establishing expanded potential stem cells for other mammalian species.

ERK1 is dispensable for mouse pancreatic beta cell function but is necessary for glucose-induced full activation of MSK1 and CREB

AIMS/HYPOTHESIS

Insufficient insulin secretion from pancreatic beta cells, which is associated with a decrease in beta cell mass, is a characteristic of type 2 diabetes. Extracellular signal-related kinase 1 and 2 (ERK1/2) inhibition in beta cells has been reported to affect insulin secretion, gene transcription and survival, although whether ERK1 and ERK2 play distinct roles is unknown. The aim of this study was to assess the individual roles of ERK1 and ERK2 in beta cells using ERK1 (also known as Mapk3)-knockout mice (Erk1 ^-/- mice) and pharmacological approaches.

METHODS

NAD(P)H, free cytosolic Ca²⁺ concentration and insulin secretion were determined in islets. ERK1 and ERK2 subplasmalemmal translocation and activity was monitored using total internal reflection fluorescence microscopy. ERK1/2, mitogen and stress-activated kinase1 (MSK1) and cAMP-responsive element-binding protein (CREB) activation were evaluated by western blot and/or immunocytochemistry. The islet mass was determined from pancreatic sections.

RESULTS

Glucose induced rapid subplasmalemmal recruitment of ERK1 and ERK2. When both ERK1 and ERK2 were inhibited simultaneously, the rapid transient peak of the first phase of glucose-induced insulin secretion was reduced by 40% (p < 0.01), although ERK1 did not appear to be involved in this process. By contrast, ERK1 was required for glucose-induced full activation of several targets involved in beta cell survival; MSK1 and CREB were less active in Erk1 ^-/- mouse beta cells (p < 0.01) compared with Erk1 ^+/+ mouse beta cells, and their phosphorylation could only be restored when ERK1 was re-expressed and not when ERK2 was overexpressed. Finally, the islet mass of Erk1 ^-/- mice was slightly increased in young animals (4-month-old mice) vs Erk1 ^+/+ mice (section occupied by islets [mean ± SEM]: 0.74% ± 0.03% vs 0.62% ± 0.04%; p < 0.05), while older mice (10 months old) were less prone to age-associated pancreatic peri-insulitis (infiltrated islets [mean ± SEM]: 7.51% ± 1.34% vs 2.03% ± 0.51%; p < 0.001).

CONCLUSIONS/INTERPRETATION

ERK1 and ERK2 play specific roles in beta cells. ERK2 cannot always compensate for the lack of ERK1 but the absence of a clear-cut phenotype in Erk1 ^-/- mice shows that ERK1 is dispensable in normal conditions.

Dual Specificity Phosphatase 5-Substrate Interaction: A Mechanistic Perspective

The mammalian genome contains approximately 200 phosphatases that are responsible for catalytically removing phosphate groups from proteins. In this review, we discuss dual specificity phosphatase 5 (DUSP5). DUSP5 belongs to the dual specificity phosphatase (DUSP) family, so named after the family members' abilities to remove phosphate groups from serine/threonine and tyrosine residues. We provide a comparison of DUSP5's structure to other DUSPs and, using molecular modeling studies, provide an explanation for DUSP5's mechanistic interaction and specificity toward phospho-extracellular regulated kinase, its only known substrate. We also discuss new insights from molecular modeling studies that will influence our current thinking of mitogen-activated protein kinase signaling. Finally, we discuss the lessons learned from identifying small molecules that target DUSP5, which might benefit targeting efforts for other phosphatases. © 2017 American Physiological Society. Compr Physiol 7:1449-1461, 2017.

From the stem of the placental tree: trophoblast stem cells and their progeny

Trophoblast stem cells (TSCs) retain the capacity to self-renew indefinitely and harbour the potential to differentiate into all trophoblast subtypes of the placenta. Recent studies have shown how signalling cascades integrate with transcription factor circuits to govern the fine balance between TSC self-renewal and differentiation. In addition, breakthroughs in reprogramming strategies have enabled the generation of TSCs from fibroblasts, opening up exciting new avenues that may allow the isolation of this stem cell type from other species, notably humans. Here, we review these recent advances in light of their importance for understanding placental pathologies and developing personalised medicine approaches for pregnancy complications.

Noonan syndrome: lessons learned from genetically modified mouse models

Noonan syndrome is a RASopathy that results from activating mutations in different members of the RAS/MAPK signaling pathway. At least eleven members of this pathway have been found mutated, PTPN11 being the most frequently mutated gene affecting about 50% of the patients, followed by SOS1 (10%), RAF1 (10%) and KRAS (5%). Recently, even more infrequent mutations have been newly identified by next generation sequencing. This spectrum of mutations leads to a broad variety of clinical symptoms such as cardiopathies, short stature, facial dysmorphia and neurocognitive impairment. The genetic variability of this syndrome makes it difficult to establish a genotype-phenotype correlation, which will greatly help in the clinical management of the patients. Areas covered: Studies performed with different genetically engineered mouse models (GEMMs) developed up to date. Expert commentary: GEMMs have helped us understand the role of some genes and the effect of the different mutations in the development of the syndrome. However, few models have been developed and more characterization of the existing ones should be performed to learn about the impact of the different modifiers in the phenotypes, the potential cancer risk in patients, as well as preventative and therapeutic strategies.

The extracellular signal-regulated kinase 1/2 pathway in neurological diseases: A potential therapeutic target (Review)

Signaling pathways are critical modulators of a variety of physiological and pathological processes, and the abnormal activation of some signaling pathways can contribute to disease progression in various conditions. As a result, signaling pathways have emerged as an important tool through which the occurrence and development of diseases can be studied, which may then lead to the development of novel drugs. Accumulating evidence supports a key role for extracellular signal-regulated kinase 1/2 (ERK1/2) signaling in the embryonic development of the central nervous system (CNS) and in the regulation of adult brain function. ERK1/2, one of the most well characterized members of the mitogen-activated protein kinase family, regulates a range of processes, from metabolism, motility and inflammation, to cell death and survival. In the nervous system, ERK1/2 regulates synaptic plasticity, brain development and repair as well as memory formation. ERK1/2 is also a potent effector of neuronal death and neuroinflammation in many CNS diseases. This review summarizes recent findings in neurobiological ERK1/2 research, with a special emphasis on findings that clarify our understanding of the processes that regulate the plethora of isoform-specific ERK functions under physiological and pathological conditions. Finally, we suggest some potential therapeutic strategies associated with agents acting on the ERK1/2 signaling to prevent or treat neurological diseases.

Mitogen-Activated Protein Kinase Activity Is Not Essential for the First Step of Nuclear Reprogramming in Bovine Somatic Cell Nuclear Transfer

For reprogramming a somatic nucleus during mammalian cloning, metaphase of the second meiotic division (MII) oocytes has been widely used as recipient cytoplasm. High activity of maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK) is believed to accelerate the remodeling and/or reprogramming of a somatic nucleus introduced into the ooplasm by somatic cell nuclear transfer. We demonstrated previously that the first step in nuclear reprogramming is not directly regulated by MPF and MAPK because activated oocytes in which MPF activity is diminished and MAPK activity is maintained can develop to the blastocyst stage after receiving an M phase somatic nucleus in bovine cloning. In this study, our aim was to test whether MAPK activity is necessary for the first step in nuclear reprogramming and/or chromatin remodeling (phosphorylation of histone H3 at Ser3, trimethylation of histone H3 at Lys 9, and acetylation of histone H3 at Lys14) in bovine somatic cloning. We found that it was not necessary, and neither was MPF activity.

pERK1/2 Peripheral Recruitment and Filopodia Protrusion Augment Oligodendrocyte Progenitor Cell Migration: Combined Effects of PDGF-A and Fibronectin

Oligodendrocyte progenitor cell (OPC) migration is critical for effective myelination of the central nervous system. Not only during normal myelination but also during remyelination, the growth factors (GFs) and extracellular matrix (ECM) protein affect the OPC migration. Studies showed the altered levels of GFs and ECM in the demyelinating lesions. In our earlier studies, we have shown that the effect of platelet-derived growth factor alpha (PDGF-A) on OPC migration is dose- and time-dependent. In that we have shown that the physiological concentration (1 ng/ml) of PDGF-A was unable to induce OPC migration at transient exposure (30 min). However, the involvement of ECM in the regulation of PDGF-A mediated OPC migration was not clear. In the present study, we have used fibronectin (FN) as ECM. PDGF-A and FN have similar and overlapping intracellular signaling pathways including the extracellular regulated kinases 1 and 2 (ERK1/2). Here we demonstrate how physiological concentration of PDGF-A combines with FN to augment OPC migration in vitro. The present study is first of its kind to show the importance of the synergistic effects of PDGF-A and FN on peripheral recruitment of phosphorylated/activated ERK1/2 (pERK1/2), actin-pERK1/2 co-localization, and filopodia formation, which are essential for the enhanced OPC migration. These findings were further confirmed by ERK1/2 inhibition studies, using the pharmacological inhibitor U0126. An understanding of these complex interactions may lead to additional strategies for transplanting genetically modified OPCs to repair widespread demyelinated lesions.

Modeling RASopathies with Genetically Modified Mouse Models

The RAS/MAPK signaling pathway plays key roles in development, cell survival and proliferation, as well as in cancer pathogenesis. Molecular genetic studies have identified a group of developmental syndromes, the RASopathies, caused by germ line mutations in this pathway. The syndromes included within this classification are neurofibromatosis type 1 (NF1), Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NS-ML, formerly known as LEOPARD syndrome), Costello syndrome (CS), cardio-facio-cutaneous syndrome (CFC), Legius syndrome (LS, NF1-like syndrome), capillary malformation-arteriovenous malformation syndrome (CM-AVM), and hereditary gingival fibromatosis (HGF) type 1. Although these syndromes present specific molecular alterations, they are characterized by a large spectrum of functional and morphological abnormalities, which include heart defects, short stature, neurocognitive impairment, craniofacial malformations, and, in some cases, cancer predisposition. The development of genetically modified animals, such as mice (Mus musculus), flies (Drosophila melanogaster), and zebrafish (Danio rerio), has been instrumental in elucidating the molecular and cellular bases of these syndromes. Moreover, these models can also be used to determine tumor predisposition, the impact of different genetic backgrounds on the variable phenotypes found among the patients and to evaluate preventative and therapeutic strategies. Here, we review a wide range of genetically modified mouse models used in the study of RASopathies and the potential application of novel technologies, which hopefully will help us resolve open questions in the field.

Ask1 regulates murine platelet granule secretion, thromboxane A2 generation, and thrombus formation

Mitogen-activated protein kinases (MAPKs) are expressed in platelets and are activated downstream of physiological agonists. Pharmacological and genetic evidence indicate that MAPKs play a significant role in hemostasis and thrombosis, but it is not well understood how MAPKs are activated upon platelet stimulation. Here, we show that apoptosis signal-regulating kinase 1 (ASK1), a member of the MAP3K family, is expressed in both human and murine platelets. ASK1 is rapidly and robustly activated upon platelet stimulation by physiological agonists. Disruption of Ask1 (Ask1^-/- ) resulted in a marked functional defect in platelets. Ask1^-/- platelets showed an impaired agonist-induced integrin α_IIbβ₃ activation and platelet aggregation. Although there was no difference in Ca²⁺ rise, platelet granule secretion and thromboxane A₂ (TxA₂) generation were significantly attenuated in Ask1^-/- platelets. The defective granule secretion observed in Ask1^-/- platelets was a consequence of impaired TxA₂ generation. Biochemical studies showed that platelet agonists failed to activate p38 MAPK in Ask1^-/- platelets. On the contrary, activation of c-Jun N-terminal kinases and extracellular signal-regulated kinase 1/2 MAPKs was augmented in Ask1^-/- platelets. The defect in p38 MAPK results in failed phosphorylation of cPLA₂ in Ask1^-/- platelets and impaired platelet aggregate formation under flow. The absence of Ask1 renders mice defective in hemostasis as assessed by prolonged tail-bleeding times. Deletion of Ask1 also reduces thrombosis as assessed by delayed vessel occlusion of carotid artery after FeCl₃-induced injury and protects against collagen/epinephrine-induced pulmonary thromboembolism. These results suggest that the platelet Ask1 plays an important role in regulation of hemostasis and thrombosis.

The Role of ERK1/2 in the Development of Diabetic Cardiomyopathy

Diabetes mellitus is a chronic metabolic condition that affects carbohydrate, lipid and protein metabolism and may impair numerous organs and functions of the organism. Cardiac dysfunction afflicts many patients who experience the oxidative stress of the heart. Diabetic cardiomyopathy (DCM) is one of the major complications that accounts for more than half of diabetes-related morbidity and mortality cases. Chronic hyperglycemia and hyperlipidemia from diabetes mellitus cause cardiac oxidative stress, endothelial dysfunction, impaired cellular calcium handling, mitochondrial dysfunction, metabolic disturbances, and remodeling of the extracellular matrix, which ultimately lead to DCM. Although many studies have explored the mechanisms leading to DCM, the pathophysiology of DCM has not yet been fully clarified. In fact, as a potential mechanism, the associations between DCM development and mitogen-activated protein kinase (MAPK) activation have been the subjects of tremendous interest. Nonetheless, much remains to be investigated, such as tissue- and cell-specific processes of selection of MAPK activation between pro-apoptotic vs. pro-survival fate, as well as their relation with the pathogenesis of diabetes and associated complications. In general, it turns out that MAPK signaling pathways, such as extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK) and p38 MAP kinase, are demonstrated to be actively involved in myocardial dysfunction, hypertrophy, fibrosis and heart failure. As one of MAPK family members, the activation of ERK1/2 has also been known to be involved in cardiac hypertrophy and dysfunction. However, many recent studies have demonstrated that ERK1/2 signaling activation also plays a crucial role in FGF21 signaling and exerts a protective environment of glucose and lipid metabolism, therefore preventing abnormal healing and cardiac dysfunction. The duration, extent, and subcellular compartment of ERK1/2 activation are vital to differential biological effects of ERK1/2. Moreover, many intracellular events, including mitochondrial signaling and protein kinases, manipulate signaling upstream and downstream of MAPK, to influence myocardial survival or death. In this review, we will summarize the roles of ERK1/2 pathways in DCM development by the evidence from current studies and will present novel opinions on "differential influence of ERK1/2 action in cardiac dysfunction, and protection against myocardial ischemia-reperfusion injury".

Isolation of Mouse Embryonic Stem Cell Lines in the Study of ERK1/2 MAP Kinase Signaling

Mouse embryonic stem (ES) cells have proven to be invaluable research tools for dissecting the role of signaling pathways in embryonic development, adult physiology, and various diseases. ES cells are amenable to genetic manipulation by classical gene targeting via homologous recombination or by genome editing technologies. These cells can be used to generate genetically modified mouse models or to study the signaling circuitry regulating self-renewal and early lineage commitment. In this chapter, we describe methods used for the isolation and establishment of mouse ES cell lines from blastocyst embryos and for the measurement of ERK1/2 activity in ES cells.

Mitogen-activated protein kinase 1 from disk abalone (Haliotis discus discus): Roles in early development and immunity-related transcriptional responses

Mitogen-activated protein kinase (MAPK) is involved in the regulation of cellular events by mediating signal transduction pathways. MAPK1 is a member of the extracellular-signal regulated kinases (ERKs), playing roles in cell proliferation, differentiation, and development. This is mainly in response to growth factors, mitogens, and many environmental stresses. In the current study, we have characterized the structural features of a homolog of MAPK1 from disk abalone (AbMAPK1). Further, we have unraveled its expressional kinetics against different experimental pathogenic infections or related chemical stimulants. AbMAPK1 harbors a 5' untranslated region (UTR) of 23 bps, a coding sequence of 1104 bps, and a 3' UTR of 448 bp. The putative peptide comprises a predicted molecular mass of 42.2 kDa, with a theoretical pI of 6.28. Based on the in silico analysis, AbMAPK1 possesses two N-glycosylation sites, one S_TK catalytic domain, and a conserved His-Arg-Asp domain (HRD). In addition, a conservative glycine rich ATP-phosphate-binding loop and a threonine-x-tyrosine motif (TEY) important for the autophosphorylation were also identified in the protein. Homology assessment of AbMAPK1 showed several conserved regions, and ark clam (Aplysia californica) showed the highest sequence identity (87.9%). The phylogenetic analysis supported close evolutionary kinship with molluscan orthologs. Constitutive expression of AbMAPK1 was observed in six different tissues of disk abalone, with the highest expression in the digestive tract, followed by the gills and hemocytes. Highest AbMAPK1 mRNA expression level was detected at the trochophore developmental stage, suggesting its role in abalone cell differentiation and proliferation. Significant modulation of AbMAPK1 expression under pathogenic stress suggested its putative involvement in the immune defense mechanism.

Redundancy in the World of MAP Kinases: All for One

The protein kinases ERK1 and ERK2 are the effector components of the prototypical ERK1/2 mitogen-activated protein (MAP) kinase pathway. This signaling pathway regulates cell proliferation, differentiation and survival, and is essential for embryonic development and cellular homeostasis. ERK1 and ERK2 homologs share similar biochemical properties but whether they exert specific physiological functions or act redundantly has been a matter of controversy. However, recent studies now provide compelling evidence in support of functionally redundant roles of ERK1 and ERK2 in embryonic development and physiology. In this review, we present a critical assessment of the evidence for the functional specificity or redundancy of MAP kinase isoforms. We focus on the ERK1/ERK2 pathway but also discuss the case of JNK and p38 isoforms.

Naringenin-induced migration of embrynoic trophectoderm cells is mediated via PI3K/AKT and ERK1/2 MAPK signaling cascades

For successful pregnancy, a well-coordinated network of growth factors, nutrients and hormones is required for fetal-maternal interactions. Naringenin, as a weak phytoestrogen, improves diabetes, inflammation, neuronal diseases, cardiovascular diseases and cancers. However, the role of naringenin in migration mechanism(s) of peri-implantation conceptuses is unknown. Therefore, in the present study, we determined the effects of naringenin on migration of porcine trophectoderm (pTr) cells, which is a known in vitro model for research on trophectoderm cell biology and placental-fetal developmental biology, in order to assess intracellular signal transduction pathways activated by naringenin. Migration of pTr cells increased in a dose-dependent manner in response to naringenin. Also, naringenin activated the phosphorylation of AKT and ERK1/2 proteins in a dose-dependent manner and those proteins were abundant mainly in the cytoplasm of naringenin-treated pTr cells. Within 30 min after treatment with 20 μM naringenin, the abundance of phosphorylated EKR1/2, P70S6K, P90RSK and S6K proteins increased, and then returned to basal levels by 120 min whereas the abundance of AKT increased gradually to 120 min post-treatment. However, the phosphorylation of AKT, P70S6K, P90RSK and S6K was reduced in naringenin-induced pTr cells pre-treated with a PI3K inhibitor (LY294002). Also, a MEK1/2 inhibitor (U0126) significantly decreased naringenin-induced phosphorylation of ERK1/2, P70S6K and S6K proteins in pTr cells. Moreover, the naringenin-stimulated migration of pTr cells was suppressed by LY294002 and U0126. Collectively, results of the present study suggest that naringenin supports migration of pTr cells through PI3K/AKT and ERK1/2 MAPK signaling pathways crucial for orchestrating conceptus-uterine interactions.

ERK1 and ERK2 Map Kinases: Specific Roles or Functional Redundancy?

The MAP kinase signaling cascade Ras/Raf/MEK/ERK has been involved in a large variety of cellular and physiological processes that are crucial for life. Many pathological situations have been associated to this pathway. More than one isoform has been described at each level of the cascade. In this review we devoted our attention to ERK1 and ERK2, which are the effector kinases of the pathway. Whether ERK1 and ERK2 specify functional differences or are in contrast functionally redundant, constitutes an ongoing debate despite the huge amount of studies performed to date. In this review we compiled data on ERK1 vs. ERK2 gene structures, protein sequences, expression levels, structural and molecular mechanisms of activation and substrate recognition. We have also attempted to perform a rigorous analysis of studies regarding the individual roles of ERK1 and ERK2 by the means of morpholinos, siRNA, and shRNA silencing as well as gene disruption or gene replacement in mice. Finally, we comment on a recent study of gene and protein evolution of ERK isoforms as a distinct approach to address the same question. Our review permits the evaluation of the relevance of published studies in the field especially when measurements of global ERK activation are taken into account. Our analysis favors the hypothesis of ERK1 and ERK2 exhibiting functional redundancy and points to the concept of the global ERK quantity, and not isoform specificity, as being the essential determinant to achieve ERK function.

Single-stranded DNA binding protein Ssbp3 induces differentiation of mouse embryonic stem cells into trophoblast-like cells

BACKGROUND

Intrinsic factors and extrinsic signals which control unlimited self-renewal and developmental pluripotency in embryonic stem cells (ESCs) have been extensively investigated. However, a much smaller number of factors involved in extra-embryonic trophoblast differentiation from ESCs have been studied. In this study, we investigated the role of the single-stranded DNA binding protein, Ssbp3, for the induction of trophoblast-like differentiation from mouse ESCs.

METHODS

Gain- and loss-of-function experiments were carried out through overexpression or knockdown of Ssbp3 in mouse ESCs under self-renewal culture conditions. Expression levels of pluripotency and lineage markers were detected by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analyses. The global gene expression profile in Ssbp3-overexpressing cells was determined by affymetrix microarray. Gene ontology and pathway terms were analyzed and further validated by qRT-PCR and Western blotting. The methylation status of the Elf5 promoter in Ssbp3-overexpressing cells was detected by bisulfite sequencing. The trophoblast-like phenotype induced by Ssbp3 was also evaluated by teratoma formation and early embryo injection assays.

RESULTS

Forced expression of Ssbp3 in mouse ESCs upregulated expression levels of lineage-associated genes, with trophoblast cell markers being the highest. In contrast, depletion of Ssbp3 attenuated the expression of trophoblast lineage marker genes induced by downregulation of Oct4 or treatment with BMP4 and bFGF in ESCs. Interestingly, global gene expression profiling analysis indicated that Ssbp3 overexpression did not significantly alter the transcript levels of pluripotency-associated transcription factors. Instead, Ssbp3 promoted the expression of early trophectoderm transcription factors such as Cdx2 and activated MAPK/Erk1/2 and TGF-β pathways. Furthermore, overexpression of Ssbp3 reduced the methylation level of the Elf5 promoter and promoted the generation of teratomas with internal hemorrhage, indicative of the presence of trophoblast cells.

CONCLUSIONS

This study identifies Ssbp3, a single-stranded DNA binding protein, as a regulator for mouse ESCs to differentiate into trophoblast-like cells. This finding is helpful to understand the regulatory networks for ESC differentiation into extra-embryonic lineages.

Uterine Expression of NDRG4 Is Induced by Estrogen and Up-Regulated during Embryo Implantation Process in Mice

Embryo implantation is an essential step for the establishment of pregnancy and dynamically regulated by estrogen and progesterone. NDRG4 (N-myc down-regulated gene 4) is a tumor suppressor that participates in cell survival, tumor invasion and angiogenesis. The objective of this study was to preliminarily explore the role of NDRG4 in embryo implantation. By immunohistochemistry (IHC) and quantitive RT-PCR (qRT-PCR), we found that uterine expression of NDRG4 was increased along with puberal development, and its expression in adult females reached the peak at the estrus stage during the estrus cycle. Furthermore, uterine NDRG4 expression was significantly induced by the treatment of estradiol (E₂) both in pre-puberty females and ovariectomized adult females. Uterine expression pattern of NDRG4 during the peri-implantation period in mice was determined by IHC, qRT-PCR and Western blot. It was observed that NDRG4 expression was up-regulated during the implantation process, and its expression level at the implantation sites was significantly higher than that at the inter-implantation sites. Meanwhile, an increased expression in NDRG4 was associated with artificial decidualization as well as the activation of delayed implantation. By qRT-PCR and Western blot, we found that the in vitro decidualization of endometrial stromal cells (ESCs) was accompanied by up-regulation of NDRG4 expression, whereas knockdown of its expression in these cells by siRNA inhibited the decidualization process. In addition, Western blot analysis showed that NDRG4 protein expression was decreased in human villus tissues of recurrent miscarriage (RM) patients compared to normal pregnant women. Collectively, these data suggested that uterine NDRG4 expression could be induced by estrogen, and NDRG4 might play an important role during early pregnancy.

Genetic insights into the mechanisms of Fgf signaling

The fibroblast growth factor (Fgf) family of ligands and receptor tyrosine kinases is required throughout embryonic and postnatal development and also regulates multiple homeostatic functions in the adult. Aberrant Fgf signaling causes many congenital disorders and underlies multiple forms of cancer. Understanding the mechanisms that govern Fgf signaling is therefore important to appreciate many aspects of Fgf biology and disease. Here we review the mechanisms of Fgf signaling by focusing on genetic strategies that enable in vivo analysis. These studies support an important role for Erk1/2 as a mediator of Fgf signaling in many biological processes but have also provided strong evidence for additional signaling pathways in transmitting Fgf signaling in vivo.

Delineation of a recognizable phenotype for the recurrent LCR22-C to D/E atypical 22q11.2 deletion

The 22q11.2 deletion syndrome is typically caused by haploinsufficiency of a 3 Mb region that extends from LCR22-A until LCR22-D, while the recurrent recombination between any of the LCR22-D to H causes the 22q11.2 distal deletion syndrome. Here, we describe three patients with a de novo atypical ∼1.4 Mb 22q11.2 deletion that involves LCR22-C to a region beyond D (LCR22-C to D/E), encompassing the distal portion of the typical deleted region and the proximal portion of the distal deletion. We also review six previous published patients with the same rearrangement and compare their features with those found in patients with overlapping deletions. Patients with LCR22-C to D/E deletion present a recognizable phenotype characterized by facial dysmorphic features, high frequency of cardiac defects, including conotruncal defects, prematurity, growth restriction, microcephaly, and mild developmental delay. Genotype-phenotype analysis of the patients indicates that CRKL and MAPK1 genes play an important role as causative factors for the main clinical features of the syndrome. In particular, CRKL gene seems to be involved in the occurrence of conotruncal cardiac anomalies, mainly tetralogy of Fallot. © 2016 Wiley Periodicals, Inc.

Intracellular signaling pathway regulation of myelination and remyelination in the CNS

The restoration of myelin sheaths on demyelinated axons remains a major obstacle in the treatment of multiple sclerosis (MS). Currently approved therapies work by modulating the immune system to reduce the number and rate of lesion formation but are only partially effective since they are not able to restore lost myelin. In the healthy CNS, myelin continues to be generated throughout life and spontaneous remyelination occurs readily in response to insults. In patients with MS, however, remyelination eventually fails, at least in part as a result of a failure of oligodendrocyte precursor cell (OPC) differentiation and the subsequent production of new myelin. A better understanding of the molecular mechanisms and signaling pathways that drive the process of myelin sheath formation is therefore important in order to speed the development of novel therapeutics designed to target remyelination. Here we review data supporting critical roles for three highly conserved intracellular signaling pathways: Wnt/β-catenin, PI3K/AKT/mTOR, and ERK/MAPK in the regulation of OPC differentiation and myelination both during development and in remyelination. Potential points of crosstalk between the three pathways and important areas for future research are also discussed.

Epigenesis and plasticity of mouse trophoblast stem cells

The critical role of the placenta in supporting a healthy pregnancy is mostly ensured by the extraembryonic trophoblast lineage that acts as the interface between the maternal and the foetal compartments. The diverse trophoblast cell subtypes that form the placenta originate from a single layer of stem cells that emerge from the embryo when the earliest cell fate decisions are occurring. Recent studies show that these trophoblast stem cells exhibit extensive plasticity as they are capable of differentiating down multiple pathways and are easily converted into embryonic stem cells in vitro. In this review, we discuss current knowledge of the mechanisms and control of the epigenesis of mouse trophoblast stem cells through a comparison with the corresponding mechanisms in pluripotent embryonic stem cells. To illustrate some of the more striking manifestations of the epigenetic plasticity of mouse trophoblast stem cells, we discuss them within the context of two paradigms of epigenetic regulation of gene expression: the imprinted gene expression of specific loci and the process of X-chromosome inactivation.

Inhibition of MEK1 Signaling Pathway in the Liver Ameliorates Insulin Resistance

Although mitogen-activated protein kinase kinase (MEK) is a key signaling molecule and a negative regulator of insulin action, it is still uncertain whether MEK can be a therapeutic target for amelioration of insulin resistance (IR) in type 2 diabetes (T2D) in vivo. To clarify whether MEK inhibition improves T2D, we examined the effect of continuous MEK inhibition with two structurally different MEK inhibitors, RO5126766 and RO4987655, in mouse models of T2D. RO5126766 and RO4987655 were administered via dietary admixture. Both compounds decreased blood glucose and improved glucose tolerance in doses sufficient to sustain inhibition of extracellular signal-regulated kinase (ERK)1/2 phosphorylation downstream of MEK in insulin-responsive tissues in db/db mice. A hyperinsulinemic-euglycemic clamp test showed increased glucose infusion rate (GIR) in db/db mice treated with these compounds, and about 60% of the increase was attributed to the inhibition of endogenous glucose production, suggesting that the liver is responsible for the improvement of IR. By means of adenovirus-mediated Mek1 shRNA expression, we confirmed that blood glucose levels are reduced by suppression of MEK1 expression in the liver of db/db mice. Taken together, these results suggested that the MEK signaling pathway could be a novel therapeutic target for novel antidiabetic agents.

The Stress-Response MAP Kinase Signaling in Cardiac Arrhythmias

Stress-response kinases, the mitogen-activated protein kinases (MAPKs) are activated in response to the challenge of a myriad of stressors. c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and p38 MAPKs are the predominant members of the MAPK family in the heart. Extensive studies have revealed critical roles of activated MAPKs in the processes of cardiac injury and heart failure and many other cardiovascular diseases. Recently, emerging evidence suggests that MAPKs also promote the development of cardiac arrhythmias. Thus, understanding the functional impact of MAPKs in the heart could shed new light on the development of novel therapeutic approaches to improve cardiac function and prevent arrhythmia development in the patients. This review will summarize the recent findings on the role of MAPKs in cardiac remodeling and arrhythmia development and point to the critical need of future studies to further elucidate the fundamental mechanisms of MAPK activation and arrhythmia development in the heart.

Tpbpa mediated deletion of Tfap2c leads to deregulation of MAPK, P21, AKT and subsequent placental growth arrest

Loss of Tfap2c leads to developmental defects in the extra-embryonic compartment with embryonic lethality at E7.5. To investigate requirement of Tfap2c in later placental development, deletion of Tfap2c was induced throughout extra-embryonic ectoderm at E6.5 leading to severe placental abnormalities caused by reduced trophoblast population resulting in embryonic retardation by E8.5. Deletion of Tfap2c in Tpbpa+ progenitors at E8.5 results in growth arrest of junctional zone. TFAP2C regulates its target genes p21/Cdkn1a and Dusp6, involved in repression of MAPK signaling. Loss of TFAP2C reduces activation of ERK1/2 in the placenta. Downregulation of Akt and reduced activation of pAKT in the mutant placenta are accompanied by impaired glycogen synthesis. Loss of Tfap2c led to upregulation of imprinted gene H19 and downregulation of Tex19.1 and Ascl2. The placental insufficiency post E16.5 causes fetal growth restriction with 19% lighter mutant pups. TFAP2C knockdown in human trophoblast choriocarcinoma JAr cells inhibited MAPK and AKT signaling. Thus, we present a model where Tfap2c in trophoblasts controls proliferation by repressing P21 and activating MAPK pathway and further supporting differentiation of glycogen cells via activating Akt pathway.

Altered ERK1/2 Signaling in the Brain of Learned Helpless Rats: Relevance in Vulnerability to Developing Stress-Induced Depression

Extracellular signal-regulated kinase 1/2- (ERK1/2-) mediated cellular signaling plays a major role in synaptic and structural plasticity. Although ERK1/2 signaling has been shown to be involved in stress and depression, whether vulnerability to develop depression is associated with abnormalities in ERK1/2 signaling is not clearly known. The present study examined ERK1/2 signaling in frontal cortex and hippocampus of rats that showed vulnerability (learned helplessness, (LH)) or resiliency (non-learned helplessness, (non-LH)) to developing stress-induced depression. In frontal cortex and hippocampus of LH rats, we found that mRNA and protein expressions of ERK1 and ERK2 were significantly reduced, which was associated with their reduced activation and phosphorylation in cytosolic and nuclear fractions, where ERK1 and ERK2 target their substrates. In addition, ERK1/2-mediated catalytic activities and phosphorylation of downstream substrates RSK1 (cytosolic and nuclear) and MSK1 (nuclear) were also lower in the frontal cortex and hippocampus of LH rats without any change in their mRNA or protein expression. None of these changes were evident in non-LH rats. Our study indicates that ERK1/2 signaling is differentially regulated in LH and non-LH rats and suggests that abnormalities in ERK1/2 signaling may be crucial in the vulnerability to developing depression.

Fgfr1 regulates development through the combinatorial use of signaling proteins

Brewer et al. engineered an allelic series of knock-in point mutations designed to disrupt Fgfr1 signaling functions individually and in combination. They found that, in addition to Frs2, Crk proteins and Plcγ also contribute to Erk1/2 activation. Disruption of all known signaling functions diminished Erk1/2 and Plcγ activation but did not recapitulate the peri-implantation Fgfr1-null phenotype.

Fibroblast growth factor (Fgf) signaling governs multiple processes important in development and disease. Many lines of evidence have implicated Erk1/2 signaling induced through Frs2 as the predominant effector pathway downstream from Fgf receptors (Fgfrs), but these receptors can also signal through other mechanisms. To explore the functional significance of the full range of signaling downstream from Fgfrs in mice, we engineered an allelic series of knock-in point mutations designed to disrupt Fgfr1 signaling functions individually and in combination. Analysis of each mutant indicates that Frs2 binding to Fgfr1 has the most pleiotropic functions in development but also that the receptor uses multiple proteins additively in vivo. In addition to Frs2, Crk proteins and Plcγ also contribute to Erk1/2 activation, affecting axis elongation and craniofacial and limb development and providing a biochemical mechanism for additive signaling requirements. Disruption of all known signaling functions diminished Erk1/2 and Plcγ activation but did not recapitulate the peri-implantation Fgfr1-null phenotype. This suggests that Erk1/2-independent signaling pathways are functionally important for Fgf signaling in vivo.

U0126, an Inhibitor of MEK1/2, Increases Tumor Necrosis Factor-α-Induced Apoptosis, but not Interleukin-6 Induced Apoptosis in C-28/I2 Human Chondrocytes

BACKGROUND

Activation of the SAPK/MAPK signaling pathway by pro-inflammatory cytokines is known to induce apoptosis in cultured articular chondrocytes. C-28/I2, an immortalized human juvenile chondrocyte cell line was employed to determine the extent to which recombinant human (rh) forms of the pro-inflammatory cytokines, tumor necrosis factor-α (rhTNF-α,), interleukin-6 (rhIL-6) and oncostatin M (rhOSM) induced apoptosis.

METHODS

The induction of apoptosis in the presence or absence of these cytokines was measured by the DAPI/TUNEL assay, by whether or not pro-caspase-3 was activated and by the extent to which poly-ADP-ribose polymerase (PARP) was degraded.

FINDINGS

Only rhTNF-α, and rhIL-6 significantly increased apoptosis in C-28/I2 chondrocytes, although rhOSM exhibited a strong trend (p=0.067) towards increasing the frequency of apoptotic chondrocytes. The number of apoptotic C28/I2 chondrocytes was significantly increased (p=1.3 × 10-5) by the combination of rhTNF-α and U0126 (10 μM) compared to rhTNF-α alone. However apoptosis was not further increased by combining rhIL-6 with U0126. The LI-COR^® western blot system showed that U0126 (10 μM) inhibited the phosphorylation of extracellular signal-regulated kinase-2 (p-ERK2) by phorbol myristate acetate-treated immortalized myometrial cells, U0126 (10 μM) did not alter total U-ERK2. Western blot analysis also revealed that the increased frequency of apoptotic C-28/I2 chondrocytes induced by rhTNF-α and rhOSM, but not rhIL-6, was associated with PARP degradation. However, none of the cytokines resulted in pro-caspase-3 activation.

CONCLUSION

These results showed that rhTNF-α and rhIL-6 were strong inducers of apoptosis in the immortalized C-28/I2 human chondrocyte cell line. They also suggested that inhibiting ERK2 phosphorylation via U0126-mediated inhibition of MEK1/2 activity, increased rhTNF-α-induced C-28/I2 chondrocyte apoptosis.

Novel Reporter for Faithful Monitoring of ERK2 Dynamics in Living Cells and Model Organisms

Uncoupling of ERK1/2 phosphorylation from subcellular localization is essential towards the understanding of molecular mechanisms that control ERK1/2-mediated cell-fate decision. ERK1/2 non-catalytic functions and discoveries of new specific anchors responsible of the subcellular compartmentalization of ERK1/2 signaling pathway have been proposed as regulation mechanisms for which dynamic monitoring of ERK1/2 localization is necessary. However, studying the spatiotemporal features of ERK2, for instance, in different cellular processes in living cells and tissues requires a tool that can faithfully report on its subcellular distribution. We developed a novel molecular tool, ERK2-LOC, based on the T2A-mediated coexpression of strictly equimolar levels of eGFP-ERK2 and MEK1, to faithfully visualize ERK2 localization patterns. MEK1 and eGFP-ERK2 were expressed reliably and functionally both in vitro and in single living cells. We then assessed the subcellular distribution and mobility of ERK2-LOC using fluorescence microscopy in non-stimulated conditions and after activation/inhibition of the MAPK/ERK1/2 signaling pathway. Finally, we used our coexpression system in Xenopus laevis embryos during the early stages of development. This is the first report on MEK1/ERK2 T2A-mediated coexpression in living embryos, and we show that there is a strong correlation between the spatiotemporal subcellular distribution of ERK2-LOC and the phosphorylation patterns of ERK1/2. Our approach can be used to study the spatiotemporal localization of ERK2 and its dynamics in a variety of processes in living cells and embryonic tissues.

Substrate-Dependent Activity of ERK and MEK Proteins in Breast Cancer (MCF7), and Kidney Embryonic (Hek-293) Cell Lines, Cultured on Different Substrates

BACKGROUND

Breast cancer has been one of the most common types of cancer, as the leading cause of women death in world. Breast cancer has known as a heterogenic disease that the clinical path in different patients would be very different. Since the current classification has not covered the diverse clinical course of breast cancer, lots of efforts has done to find new biological markers. Integrins are hetero dimmer proteins of α and β subunits on cell membrane. After binding to extra cellular matrix (ECM), integrins activate MAPK pathway that regulated different activities like survival, differentiation, migration, immunologic response. The interaction of integrins and ECM have a key role in cancer cell activities like survival and metastasis.

OBJECTIVES

In this study the expression of αvβ3 integrin, substrate -dependent morphology and ERK and p-ERK activation was compared in MCF7 and Hek-293 cells lines.

MATERIALS AND METHODS

The expression of αvβ3 integrin was assayed by flow cytometry. These cell lines were cultured on pre-covered plates with fibronectin (FN), fibrinogen (Fg) or collagen (Col) and the expression of ERK and p-ERK proteins was assessed in attached and free cells for each substrate after 1 hour incubation. The morphology of the cells have examined under an inverted phase contrast microscope at 15 min, 1 hour, 3 hours, 5 hours and 1 day of incubatioon.

RESULTS

Different substrate induced the expression ERK or p-ERK differently in the two cell lines. In MCF7 cells, substrates induced the expression of ERK in all the attached cells but free cells in BSA, collagen and Fg showed a lower expression of ERK. In comparison with Hek-293 cells althought all the attached cells have expressed ERK peotein but only free cells in collagen plates showed the expression of ERK. None of the cell lines has shown any expression of ERK and p-ERK in attached or free cells except for the Hek-293 free cells in collagen platees that have shown a weak signal for p-ERK.

CONCLUSIONS

Overall the breast cancer cell lines MCF7 and Hek-293 cells have differently responded on similar substrates regarding morpology or ERK and MEK expressions.

Erk signaling is indispensable for genomic stability and self-renewal of mouse embryonic stem cells

Inhibition of Mek/Erk signaling by pharmacological Mek inhibitors promotes self-renewal and pluripotency of mouse embryonic stem cells (ESCs). Intriguingly, Erk signaling is essential for human ESC self-renewal. Here we demonstrate that Erk signaling is critical for mouse ESC self-renewal and genomic stability. Erk-depleted ESCs cannot be maintained. Lack of Erk leads to rapid telomere shortening and genomic instability, in association with misregulated expression of pluripotency genes, reduced cell proliferation, G1 cell-cycle arrest, and increased apoptosis. Erk signaling is also required for the activation of differentiation genes but not for the repression of pluripotency genes during ESC differentiation. Furthermore, we find an Erk-independent function of Mek, which may explain the diverse effects of Mek inhibition and Erk knockout on ESC self-renewal. Together, in contrast to the prevailing view, Erk signaling is required for telomere maintenance, genomic stability, and self-renewal of mouse ESCs.

ERK2 Alone Drives Inflammatory Pain But Cooperates with ERK1 in Sensory Neuron Survival

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) are highly homologous yet distinct components of signal transduction pathways known to regulate cell survival and function. Recent evidence indicates an isoform-specific role for ERK2 in pain processing and peripheral sensitization. However, the function of ERK2 in primary sensory neurons has not been directly tested. To dissect the isoform-specific function of ERK2 in sensory neurons, we used mice with Cre-loxP-mediated deletion of ERK2 in Nav1.8(+) sensory neurons that are predominantly nociceptors. We find that ERK2, unlike ERK1, is required for peripheral sensitization and cold sensation. We also demonstrate that ERK2, but not ERK1, is required to preserve epidermal innervation in a subset of peptidergic neurons. Additionally, deletion of both ERK isoforms in Nav1.8(+) sensory neurons leads to neuron loss not observed with deletion of either isoform alone, demonstrating functional redundancy in the maintenance of sensory neuron survival. Thus, ERK1 and ERK2 exhibit both functionally distinct and redundant roles in sensory neurons.

SIGNIFICANCE STATEMENT

ERK1/2 signaling affects sensory neuron function and survival. However, it was not clear whether ERK isoform-specific roles exist in these processes postnatally. Previous work from our laboratory suggested either functional redundancy of ERK isoforms or a predominant role for ERK2 in pain; however, the tools to discriminate between these possibilities were not available at the time. In the present study, we use new genetic knock-out lines to demonstrate that ERK2 in sensory neurons is necessary for development of inflammatory pain and for postnatal maintenance of peptidergic epidermal innervation. Interestingly, postnatal loss of both ERK isoforms leads to a profound loss of sensory neurons. Therefore, ERK1 and ERK2 display both functionally distinct and redundant roles in sensory neurons.

ERK1 and ERK2 present functional redundancy in tetrapods despite higher evolution rate of ERK1

Background

The Ras/Raf/MEK/ERK signaling pathway is involved in essential cell processes and it is abnormally activated in ~30 % of cancers and cognitive disorders. Two ERK isoforms have been described, ERK1 and ERK2; ERK2 being regarded by many as essential due to the embryonic lethality of ERK2 knock-out mice, whereas mice lacking ERK1 are viable and fertile. The controversial question of why we have two ERKs and whether they have differential functions or display functional redundancy has not yet been resolved.

Results

To investigate this question we used a novel approach based on comparing the evolution of ERK isoforms’ sequences and protein expression across vertebrates. We gathered and cloned erk1 and erk2 coding sequences and we examined protein expression of isoforms in brain extracts in all major clades of vertebrate evolution. For the first time, we measured each isoforms’ relative protein level in phylogenetically distant animals using anti-phospho antibodies targeting active ERKs. We demonstrate that squamates (lizards, snakes and geckos), despite having both genes, do not express ERK2 protein whereas other tetrapods either do not express ERK1 protein or have lost the erk1 gene. To demonstrate the unexpected squamates’ lack of ERK2 expression, we targeted each ERK isoform in lizard primary fibroblasts by specific siRNA-mediated knockdown. We also found that undetectable expression of ERK2 in lizard is compensated by a greater strength of lizard’s erk1 promoter. Finally, phylogenetic analysis revealed that ERK1 amino acids sequences evolve faster than ERK2’s likely due to genomic factors, including a large difference in gene size, rather than from functional differences since amino acids essential for function are kept invariant.

Conclusions

ERK isoforms appeared by a single gene duplication at the onset of vertebrate evolution at least 400 Mya. Our results demonstrate that tetrapods can live by expressing either one or both ERK isoforms, supporting the notion that ERK1/2 act interchangeably. Substrate recognition sites and catalytic cleft are nearly invariant in all vertebrate ERKs further suggesting functional redundancy. We suggest that future ERK research should shift towards understanding the role and regulation of total ERK quantity, especially in light of newly described erk2 gene amplification identified in tumors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0450-x) contains supplementary material, which is available to authorized users.

22q11.21 Deletion Syndromes: A Review of Proximal, Central, and Distal Deletions and Their Associated Features

Chromosome 22q11.21 contains a cluster of low-copy repeats (LCRs), referred to as LCR22A-H, that mediate meiotic non-allelic homologous recombination, resulting in either deletion or duplication of various intervals in the region. The deletion of the DiGeorge/velocardiofacial syndrome interval LCR22A-D is the most common recurrent microdeletion in humans, with an estimated incidence of ∼1:4,000 births. Deletion of other intervals in 22q11.21 have also been described, but the literature is often confusing, as the terms 'proximal', 'nested', 'distal', and 'atypical' have all been used to describe various of the other intervals. Individuals with deletions tend to have features with widely variable expressivity, even among families. This review concisely delineates each interval and classifies the reported literature accordingly.

Fgf and Esrrb integrate epigenetic and transcriptional networks that regulate self-renewal of trophoblast stem cells

Esrrb (oestrogen-related receptor beta) is a transcription factor implicated in embryonic stem (ES) cell self-renewal, yet its knockout causes intrauterine lethality due to defects in trophoblast development. Here we show that in trophoblast stem (TS) cells, Esrrb is a downstream target of fibroblast growth factor (Fgf) signalling and is critical to drive TS cell self-renewal. In contrast to its occupancy of pluripotency-associated loci in ES cells, Esrrb sustains the stemness of TS cells by direct binding and regulation of TS cell-specific transcription factors including Elf5 and Eomes. To elucidate the mechanisms whereby Esrrb controls the expression of its targets, we characterized its TS cell-specific interactome using mass spectrometry. Unlike in ES cells, Esrrb interacts in TS cells with the histone demethylase Lsd1 and with the RNA Polymerase II-associated Integrator complex. Our findings provide new insights into both the general and context-dependent wiring of transcription factor networks in stem cells by master transcription factors.

Developmental plasticity, cell fate specification and morphogenesis in the early mouse embryo

A critical point in mammalian development is when the early embryo implants into its mother's uterus. This event has historically been difficult to study due to the fact that it occurs within the maternal tissue and therefore is hidden from view. In this review, we discuss how the mouse embryo is prepared for implantation and the molecular mechanisms involved in directing and coordinating this crucial event. Prior to implantation, the cells of the embryo are specified as precursors of future embryonic and extra-embryonic lineages. These preimplantation cell fate decisions rely on a combination of factors including cell polarity, position and cell–cell signalling and are influenced by the heterogeneity between early embryo cells. At the point of implantation, signalling events between the embryo and mother, and between the embryonic and extraembryonic compartments of the embryo itself, orchestrate a total reorganization of the embryo, coupled with a burst of cell proliferation. New developments in embryo culture and imaging techniques have recently revealed the growth and morphogenesis of the embryo at the time of implantation, leading to a new model for the blastocyst to egg cylinder transition. In this model, pluripotent cells that will give rise to the fetus self-organize into a polarized three-dimensional rosette-like structure that initiates egg cylinder formation.

The p38 MAPK signalling pathway is required for glucose metabolism, lineage specification and embryo survival during mouse preimplantation development

Preimplantation embryo development is an important and unique period and is strictly controlled. This period includes a series of critical events that are regulated by multiple signal-transduction pathways, all of which are crucial in the establishment of a viable pregnancy. The p38 mitogen-activated protein kinase (MAPK) signalling pathway is one of these pathways, and inhibition of its activity during preimplantation development has a deleterious effect. The molecular mechanisms underlying the deleterious effects of p38 MAPK suppression in early embryo development remain unknown. To investigate of the effect of p38 MAPK inhibition on late preimplantation stages in detail, we cultured 2-cell stage embryos in the presence of SB203580 for 48 h and analysed the 8-cell, morula, and blastocyst stages. We determined that prolonged inhibition of the p38 MAPK altered the expression levels of Glut1 and Glut4, decreased glucose uptake during the 8-cell to blastocyst transition, changed the expression levels of transcripts which will be important to lineage commitment, including Oct4/Pou5f1, Nanog, Sox2, and Gata6, and increased cell death in 8-16 cell stage embryos onwards. Strikingly, while the expression levels of Nanog, Gata6 and Oct4/Pou5f1 mRNAs were significantly decreased, Sox2 mRNA was increased in SB203580-treated blastocysts. Taken together, our results provide important insight into the biological processes controlled by the p38 MAPK pathway and its critical role during preimplantation development.

Regulation of cell proliferation by ERK and signal-dependent nuclear translocation of ERK is dependent on Tm5NM1-containing actin filaments

Tropomyosin Tm5NM1 regulates cell proliferation and organ size. It mediates this effect by regulating the interaction of pERK and Imp7, leading to the regulation of pERK nuclear translocation. This demonstrates a role for a specific population of actin filaments in regulating a critical step in the MAPK/ERK signaling pathway.

ERK-regulated cell proliferation requires multiple phosphorylation events catalyzed first by MEK and then by casein kinase 2 (CK2), followed by interaction with importin7 and subsequent nuclear translocation of pERK. We report that genetic manipulation of a core component of the actin filaments of cancer cells, the tropomyosin Tm5NM1, regulates the proliferation of normal cells both in vitro and in vivo. Mouse embryo fibroblasts (MEFs) lacking Tm5NM1, which have reduced proliferative capacity, are insensitive to inhibition of ERK by peptide and small-molecule inhibitors, indicating that ERK is unable to regulate proliferation of these knockout (KO) cells. Treatment of wild-type MEFs with a CK2 inhibitor to block phosphorylation of the nuclear translocation signal in pERK resulted in greatly decreased cell proliferation and a significant reduction in the nuclear translocation of pERK. In contrast, Tm5NM1 KO MEFs, which show reduced nuclear translocation of pERK, were unaffected by inhibition of CK2. This suggested that it is nuclear translocation of CK2-phosphorylated pERK that regulates cell proliferation and this capacity is absent in Tm5NM1 KO cells. Proximity ligation assays confirmed a growth factor–stimulated interaction of pERK with Tm5NM1 and that the interaction of pERK with importin7 is greatly reduced in the Tm5NM1 KO cells.