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Cell fate decisions in early mammalian embryos are tightly regulated processes crucial for proper development. While FGF signaling plays key roles in early embryo patterning, its downstream effectors remain poorly understood. Our study demonstrates that the transcription factors Etv4 and Etv5 are critical mediators of FGF signaling in cell lineage specification and maturation in mouse embryos. We show that loss of Etv5 compromises primitive endoderm formation at pre-implantation stages. Furthermore, Etv4/5 deficiency delays naïve pluripotency exit and epiblast maturation, leading to elevated NANOG and reduced OTX2 expression within the blastocyst epiblast. As a consequence of delayed pluripotency progression, Etv4/5 deficient embryos exhibit anterior visceral endoderm migration defects post-implantation, a process essential for coordinated embryonic patterning and gastrulation initiation. Our results demonstrate the successive roles of these FGF signaling effectors in early lineage specification and embryonic body plan establishment, providing new insights into the molecular control of mammalian development.
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BACKGROUND: Basic trauma education for emergency department (ED) staff is available, but there are currently no advanced trauma nursing practice standards for ED nurses. OBJECTIVE: The purpose of this study was to identify consensus-based elements of an advanced trauma nursing program for ED nurses. METHODS: We used a modified Delphi process with three rounds of online survey data collection to ensure a large group of geographically diverse experts. Data were collected from February 2023 to May 2023. The sample for Round 1 was recruited from members of the Emergency Nurses Association reporting job titles, including trauma coordinator, trauma nursing core course instructor, and vice president of trauma services (n = 829). Participants in subsequent rounds were drawn from respondents to the initial invitation to participate (n = 131). Members of an emergency nursing research council with clinical and research expertise reviewed the results and provided expert input. RESULTS: An initial sample of 131 experts identified 17 elements that were assigned a median score equivalent to "agree/strongly agree" (i.e., median 4/5 or 5/5) in Round 2 (n = 69). These elements were presented in Round 3 (n = 43) to determine a rank order. Critical thinking/clinical judgment was the overall priority, followed by assessment/reassessment and early recognition of trauma. CONCLUSIONS: Emergency department trauma care experts identified priority content for advanced trauma education. Heterogeneity in the final ranking of components for this advanced trauma course, specifically differences by facility, regional, or demographic characteristics, suggests that training and education may not conform to a one-size-fits-all model.
Subject(s)
Delphi Technique , Emergency Nursing , Trauma Nursing , Humans , Emergency Nursing/education , Female , Male , Trauma Nursing/education , Surveys and Questionnaires , Adult , Curriculum , Clinical Competence , Middle AgedABSTRACT
INTRODUCTION: Charge nurses are shift leaders whose role includes managing nursing resources and facilitating appropriate patient care; in emergency departments, the charge nurse role requires both clinical and leadership skills to facilitate the flow of patients, while ensuring patient and staff safety. Literature on orientation and specific training is notably sparse. This study aimed to evaluate the content and process of core competency training and identify evaluation and implementation strategies necessary to improve charge nurse performance in United States emergency departments. METHODS: A modified Delphi technique was used in phase 1 and a qualitative content analysis method was used in phase 2 to address specific aims of the study. RESULTS: In total, 427 emergency nurse managers, directors, educators, and charge nurses responded to the initial survey to identify elements, teaching modalities, and evaluative processes; 22 participated in 1 of 2 focus groups to provide further information about the pedagogical approaches to teaching emergency charge nurse competencies. The top 5 competencies were identified as patient flow management, communication, situational awareness, clinical decision making, and nurse-patient assignment, with understanding that each competency overlapped significantly with the others. Low-fidelity simulation and gamification were identified as a preferred method of both training and evaluation. DISCUSSION: These findings have the potential to support a standardized approach to emergency charge nurse training and evaluation focusing on communication skills, clinical decision making, and situational awareness to facilitate safe and effective nurse-patient assignment and emergency department throughput.
Subject(s)
Clinical Competence , Delphi Technique , Emergency Nursing , Emergency Service, Hospital , Humans , Emergency Nursing/education , United States , Surveys and Questionnaires , Nursing, Supervisory , Focus GroupsABSTRACT
INTRODUCTION: Freestanding emergency departments (FSEDs) are emergency facilities not connected to inpatient services. The percentage of FSEDs of all EDs grew from 1% in 2001 to 12% in 2017, making FSEDs a substantial subset of US emergency care. The purpose of this study was to describe the individual attributes and environmental conditions of registered nurses working in FSEDs in the US. METHODS: A quantitative descriptive exploratory design with cross-sectional survey methodology. RESULTS: A total of 364 emergency nurses responded to the survey. Most reported their FSED was open 24 hours/day (99.5%), with board-certified emergency physicians onsite (91.5%) and a mean of 3.6 RNs working per shift. Resources immediately available in more than 50% of FSEDs included laboratory and imaging services, and in fewer than 30% of FSEDs included behavioral health care, MRI, obstetric care, orthopedic care, neurologic care, and surgical consult care. Respiratory therapy was reported by 39.6% of respondents as being immediately available. A significant minority of respondents expressed concerns about adequacy of resources and training and the effect on patient care in both survey (30% of respondents) and open-ended questions (42.5% of respondents). DISCUSSION: The practice environment of emergency nurses in FSEDs was reported as having positive elements; however, a substantial subpopulation reported serious concerns. FSEDs adhere to some of the standards put forward by the American College of Emergency Physicians, with notable exceptions in the areas of staffing RNs, staffing ancillary staff, and availability of some resources.
Subject(s)
Emergency Nursing , Emergency Service, Hospital , Humans , Emergency Service, Hospital/statistics & numerical data , United States , Cross-Sectional Studies , Emergency Nursing/statistics & numerical data , Female , Male , Adult , Surveys and Questionnaires , Middle Aged , Nursing Staff, Hospital/statistics & numerical dataABSTRACT
Recent advances in single-cell omics have transformed characterisation of cell types in challenging-to-study biological contexts. In contexts with limited single-cell samples, such as the early human embryo inference of transcription factor-gene regulatory network (GRN) interactions is especially difficult. Here, we assessed application of different linear or non-linear GRN predictions to single-cell simulated and human embryo transcriptome datasets. We also compared how expression normalisation impacts on GRN predictions, finding that transcripts per million reads outperformed alternative methods. GRN inferences were more reproducible using a non-linear method based on mutual information (MI) applied to single-cell transcriptome datasets refined with chromatin accessibility (CA) (called MICA), compared with alternative network prediction methods tested. MICA captures complex non-monotonic dependencies and feedback loops. Using MICA, we generated the first GRN inferences in early human development. MICA predicted co-localisation of the AP-1 transcription factor subunit proto-oncogene JUND and the TFAP2C transcription factor AP-2γ in early human embryos. Overall, our comparative analysis of GRN prediction methods defines a pipeline that can be applied to single-cell multi-omics datasets in especially challenging contexts to infer interactions between transcription factor expression and target gene regulation.
Subject(s)
Gene Regulatory Networks , Multiomics , Humans , Gene Regulatory Networks/genetics , Transcription Factors/metabolism , Transcriptome/genetics , Embryo, MammalianABSTRACT
BACKGROUND: The Alcohol Use Disorders Identification Test-Consumption (AUDIT-C) is a three-item screening measure of unhealthy alcohol use that is widely used in healthcare settings. Evidence shows high test-retest reliability of the AUDIT-C in research samples, but most studies had limited external validity and used small samples that could not be used to evaluate reliability across demographic subgroups and/or screening modalities. This study evaluates the test-retest reliability of the AUDIT-C completed in routine care in a large primary care sample, including across demographic subgroups defined by age, sex, race, ethnicity, and screening modality (i.e., completed in-clinic or online). METHODS: We used electronic health record (EHR) data from Kaiser Permanente Washington. The sample included 18,491 adult primary care patients who completed two AUDIT-C screens 1-21 days apart as part of routine care in 2021. Test-retest reliability was evaluated for AUDIT-C total scores (0-12) and for a binary measure indicating unhealthy alcohol use (scores ≥3 women, ≥4 men). Using previously established cutoffs, we interpreted reliability coefficients >0.75 as indicating "excellent" reliability. RESULTS: AUDIT-C screens completed in routine care and documented in EHRs had excellent test-retest reliability for total scores (ICC = 0.87, 95% CI: 0.87-0.87) and the binary indicator of unhealthy alcohol use (κ = 0.79, 95% CI: 0.78-0.80). Reliability coefficients were good to excellent across all demographic groups and for in-clinic and online modalities. Higher reliability was seen when both screens were completed through online patient portals (ICC = 0.93, 95% CI: 0.93-0.93) versus in-clinic (ICC = 0.81, 95% CI: 0.79-0.82) or when one screen was completed using each modality (ICC = 0.83, 95% CI: 0.82-0.83). Lower reliability was seen in American Indian/Alaska Native (ICC = 0.82, 95% CI: 0.75-0.87) and multiracial individuals (ICC = 0.82, 95% 0.80-0.84). CONCLUSIONS: In real-world routine care conditions, AUDIT-C screens have excellent test-retest reliability across demographic subgroups and modalities (online and in-clinic). Future research should examine why reliability varies slightly across modalities and demographic subgroups.
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Forensic DNA analysis continues to be hampered by the complex interactions between metals and DNA. Metal ions may cause direct DNA damage, inhibit DNA extraction and polymerase chain reaction (PCR) amplification or both. This study evaluated the impact of metal ions on DNA extraction, quantitation, and short tandem repeat profiling using cell-free and cellular (saliva) DNA. Of the 11 metals assessed, brass exhibited the strongest PCR inhibitory effects, for both custom and Quantifiler Trio quantitation assays. Metal ion inhibition varied across the two quantitative PCR assays and the amount of DNA template used. The Quantifiler Trio internal PCR control (IPC) only revealed evidence of PCR inhibition at higher metal ion concentrations, limiting the applicability of IPC as an indicator of the presence of metal inhibitor in a sample. Notably, ferrous ions were found to significantly decrease the extraction efficiency of the DNA-IQ DNA extraction system. The amount of DNA degradation and inhibition in saliva samples caused by metal ions increased with a dilution of the sample, suggesting that the saliva matrix provides protection from metal ion effects.
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Metals can pose challenges while conducting forensic DNA analysis. The presence of metal ions in evidence-related DNA extracts can degrade DNA or inhibit PCR as applied to DNA quantification (real-time PCR or qPCR) and/or STR amplification, leading to low success in STR profiling. Different metal ions were spiked into 0.2 and 0.5 ng of human genomic DNA in an "inhibition study" and the impact was evaluated by qPCR using the Quantifiler™ Trio DNA Quantification Kit (Thermo Fisher Scientific) and an in-house SYBR Green assay. This study reports on a contradictory finding specific to tin (Sn) ions, which caused at least a 38,000-fold overestimation of DNA concentration when utilizing Quantifiler Trio. This was explained by the raw and multicomponent spectral plots, which indicated that Sn suppresses the Quantifiler Trio passive reference dye (Mustang Purple™, MP) at ion concentrations above 0.1 mM. This effect was not observed when DNA was quantified using SYBR Green with ROX™ as the passive reference, nor when DNA was extracted and purified prior to Quantifiler Trio. The results show that metal contaminants can interfere with qPCR-based DNA quantification in unexpected ways and may be assay dependent. The results also highlight the importance of qPCR as a quality check to determine steps for sample cleanup prior to STR amplification that may be similarly impacted by metal ions. Forensic workflows should recognize the risk of inaccurate DNA quantification of samples that are collected from substrates containing tin.
Subject(s)
DNA Fingerprinting , Tin , Humans , DNA Fingerprinting/methods , Microsatellite Repeats , Real-Time Polymerase Chain Reaction , DNA/analysis , MetalsABSTRACT
The use of peripherally inserted central catheters (PICCs) has increased in cancer patients. This study aimed to compare the incidence of PICC-related bloodstream infections (PICCR-BSIs) in cancer patients treated with chemotherapy and in noncancer patients. We performed a secondary analysis from a retrospective, single-center, observational cohort. The PICCR-BSI incidence rates in cancer and noncancer patients were compared after 1:1 propensity-score matching. Then, the factors associated with PICCR-BSI were assessed in a Cox model. Among the 721 PICCs (627 patients) included in the analysis, 240 were placed in cancer patients for chemotherapy and 481 in noncancer patients. After propensity-score matching, the PICCR-BSI incidence rate was 2.6 per 1000 catheter days in cancer patients and 1.0 per 1000 catheter days in noncancer patients (p < 0.05). However, after adjusting for variables resulting in an imbalance between groups after propensity-score matching, only the number of PICC lumens was independently associated with PICCR-BSI (adjusted hazard ratio 1.81, 95% confidence interval: 1.01-3.22; p = 0.04). In conclusion, the incidence rate of PICCR-BSI is higher in cancer patients treated with chemotherapy than in noncancer patients, but our results also highlight the importance of limiting the number of PICC lumens in such patients.
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Our understanding of the molecular events driving cell specification in early mammalian development relies mainly on mouse studies, and it remains unclear whether these mechanisms are conserved across mammals, including humans. We have shown that the establishment of cell polarity via aPKC is a conserved event in the initiation of the trophectoderm (TE) placental programme in mouse, cow and human embryos. However, the mechanisms transducing cell polarity into cell fate in cow and human embryos are unknown. Here, we have examined the evolutionary conservation of Hippo signalling, which is thought to function downstream of aPKC activity, in four different mammalian species: mouse, rat, cow and human. In all four species, inhibition of the Hippo pathway by targeting LATS kinases is sufficient to drive ectopic TE initiation and downregulation of SOX2. However, the timing and localisation of molecular markers differ across species, with rat embryos more closely recapitulating human and cow developmental dynamics, compared with the mouse. Our comparative embryology approach uncovered intriguing differences as well as similarities in a fundamental developmental process among mammals, reinforcing the importance of cross-species investigations.
Subject(s)
Hippo Signaling Pathway , Signal Transduction , Cattle , Humans , Female , Pregnancy , Mice , Rats , Animals , Signal Transduction/physiology , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Blastocyst/metabolism , Placenta/metabolism , Mammals/metabolism , Cell LineageABSTRACT
BACKGROUND: Despite their spread in daily practice, few data is available on clinical factors associated with peripherally inserted central catheter (PICC)-related bloodstream infections (PR-BSI). We aimed to assess the PR-BSI incidence, microbiology, and factors associated with PR-BSI with a focus on clinical symptoms. METHODS: We conducted a retrospective cohort study in a French university hospital. We screened all PICC insertions performed from April 1st, 2018, to April 1st, 2019, and included PICC insertions in adult patients. We assessed the PR-BSI incidence, the factors associated with PR-BSI using a Cox model, and negative and positive predictive values (NPVs and PPVs) of each clinical sign for PR-BSI. RESULTS: Of the 901 PICCs inserted in 783 patients (38,320 catheters days), 214 PICCs (24%) presented with a complication. The most prevalent complication was PR-BSI (1.9 per 1000 catheter days; 8.1% of inserted PICCs ). Enterobacterales (N = 27, 37%) and coagulase negative Staphylococci (N = 24, 33%), were the main microorganisms responsible for PR-BSI. Factors independently associated with occurrence of PR-BSI were fever (hazard ratio 13.21, 95% confidence interval 6.00-29.11, p < 0.001) and chills (HR 3.66, 95%CI 1.92-6.99, p < 0.001). All clinical signs and a duration of PICC maintenance ≥ 28 days, had a low PPVs (≤ 67.1%) but high NPVs (≥ 92.5%) for PR-BSI. CONCLUSIONS: Monitoring of clinical signs, especially fever and chills, with caution and limitation of device maintenance duration, could improve PICC management.
Subject(s)
Catheter-Related Infections , Catheterization, Central Venous , Sepsis , Adult , Humans , Retrospective Studies , Catheter-Related Infections/epidemiology , Catheter-Related Infections/etiology , Chills/complications , Sepsis/epidemiology , Catheters/adverse effectsABSTRACT
Extra-embryonic mesoderm (ExM)-composed of the earliest cells that traverse the primitive streak-gives rise to the endothelium as well as haematopoietic progenitors in the developing yolk sac. How a specific subset of ExM becomes committed to a haematopoietic fate remains unclear. Here we demonstrate using an embryonic stem cell model that transient expression of the T-box transcription factor Eomesodermin (Eomes) governs haemogenic competency of ExM. Eomes regulates the accessibility of enhancers that the transcription factor stem cell leukaemia (SCL) normally utilizes to specify primitive erythrocytes and is essential for the normal development of Runx1+ haemogenic endothelium. Single-cell RNA sequencing suggests that Eomes loss of function profoundly blocks the formation of blood progenitors but not specification of Flk-1+ haematoendothelial progenitors. Our findings place Eomes at the top of the transcriptional hierarchy regulating early blood formation and suggest that haemogenic competence is endowed earlier during embryonic development than was previously appreciated.
Subject(s)
Embryonic Stem Cells/cytology , Hemangioblasts/cytology , Mesoderm/cytology , T-Box Domain Proteins/physiology , Yolk Sac/cytology , Animals , Core Binding Factor Alpha 2 Subunit/genetics , Core Binding Factor Alpha 2 Subunit/metabolism , Embryonic Stem Cells/metabolism , Female , Hemangioblasts/metabolism , Male , Mesoderm/metabolism , Mice, Knockout , Pregnancy , RNA-Seq , Single-Cell Analysis , T-Cell Acute Lymphocytic Leukemia Protein 1/genetics , T-Cell Acute Lymphocytic Leukemia Protein 1/metabolism , Vascular Endothelial Growth Factor Receptor-2/genetics , Vascular Endothelial Growth Factor Receptor-2/metabolism , Yolk Sac/metabolismSubject(s)
Mental Disorders , Opioid-Related Disorders , Substance-Related Disorders , Analgesics, Opioid/adverse effects , Humans , Mental Disorders/drug therapy , Mental Disorders/epidemiology , Mental Health , Opioid-Related Disorders/drug therapy , Opioid-Related Disorders/epidemiology , Pain/drug therapy , Prevalence , Primary Health Care , Substance-Related Disorders/drug therapy , Substance-Related Disorders/epidemiologyABSTRACT
FGF/ERK signaling is crucial for the patterning and proliferation of cell lineages that comprise the mouse blastocyst. However, ERK signaling dynamics have never been directly visualized in live embryos. To address whether differential signaling is associated with particular cell fates and states, we generated a targeted mouse line expressing an ERK-kinase translocation reporter (KTR) that enables live quantification of ERK activity at single-cell resolution. 3D time-lapse imaging of this biosensor in embryos revealed spatially graded ERK activity in the trophectoderm prior to overt polar versus mural differentiation. Within the inner cell mass (ICM), all cells relayed FGF/ERK signals with varying durations and magnitude. Primitive endoderm cells displayed higher overall levels of ERK activity, while pluripotent epiblast cells exhibited lower basal activity with sporadic pulses. These results constitute a direct visualization of signaling events during mammalian pre-implantation development and reveal the existence of spatial and temporal lineage-specific dynamics.
Subject(s)
Blastocyst/cytology , Blastocyst/enzymology , Cell Lineage , Extracellular Signal-Regulated MAP Kinases/metabolism , Signal Transduction , Animals , Cell Survival , Ectoderm/cytology , Fibroblast Growth Factors/metabolism , Mice , Mouse Embryonic Stem Cells/cytology , Time Factors , Trophoblasts/cytologyABSTRACT
BACKGROUND: Office-based buprenorphine treatment is effective for opioid use disorder. Scant research has examined programmatic factors impacting successful initiation of treatment. To increase initiation of eligible patients, our buprenorphine program implemented changes to lower treatment thresholds. Most notable among these was elimination of a requirement that patients demonstrate abstinence from stimulants prior to initiating buprenorphine. METHODS: This observational, retrospective study included patients screened for primary care-based buprenorphine treatment under high- and low-threshold conditions from 2015 to 2017. Background characteristics and treatment data were extracted from the electronic medical record and clinical registry. Chi-squared tests were used to compare proportions of patients initiated within 90 days of screening and retained to 60 days after initiation, under both conditions. Multivariate logistic regression was employed to compare relative odds of buprenorphine initiation after adjustment for several covariates. All analyses were stratified by recent stimulant use. RESULTS: The sample of 168 patients included 96 in the high-threshold group and 72 in the low-threshold group. Among patients with recent stimulant use, low-threshold conditions were associated with a higher proportion of patients initiated (69% versus 35%, p = 0.002) and higher relative odds of initiation (aOR = 7.01, 95% CI = 2.26-21.80) but also with a lower proportion of patients retained (63% versus 100%, p = 0.004). Among patients without recent stimulant use, low-threshold conditions did not change these measures by a statistically significant margin. CONCLUSIONS: Lower-threshold policies may increase buprenorphine treatment initiation for patients with co-occurring stimulant use. However, patients using stimulants may require additional supports to remain engaged.
Subject(s)
Buprenorphine/therapeutic use , Narcotic Antagonists/therapeutic use , Opiate Substitution Treatment/methods , Opioid-Related Disorders/drug therapy , Patient Participation/methods , Primary Health Care/methods , Adult , Female , Humans , Male , Middle Aged , Opioid-Related Disorders/diagnosis , Opioid-Related Disorders/psychology , Patient Participation/psychology , Retrospective Studies , Treatment OutcomeABSTRACT
Here we delineate the ontogeny of the mammalian endoderm by generating 112,217 single-cell transcriptomes, which represent all endoderm populations within the mouse embryo until midgestation. We use graph-based approaches to model differentiating cells, which provides a spatio-temporal characterization of developmental trajectories and defines the transcriptional architecture that accompanies the emergence of the first (primitive or extra-embryonic) endodermal population and its sister pluripotent (embryonic) epiblast lineage. We uncover a relationship between descendants of these two lineages, in which epiblast cells differentiate into endoderm at two distinct time points-before and during gastrulation. Trajectories of endoderm cells were mapped as they acquired embryonic versus extra-embryonic fates and as they spatially converged within the nascent gut endoderm, which revealed these cells to be globally similar but retain aspects of their lineage history. We observed the regionalized identity of cells along the anterior-posterior axis of the emergent gut tube, which reflects their embryonic or extra-embryonic origin, and the coordinated patterning of these cells into organ-specific territories.
Subject(s)
Endoderm/cytology , Endoderm/embryology , Intestines/cytology , Intestines/embryology , Single-Cell Analysis , Animals , Blastocyst/cytology , Body Patterning , Cell Differentiation , Cell Lineage , Female , Gastrulation , Male , MiceABSTRACT
The GATA zinc-finger transcription factor GATA4 is expressed in a variety of tissues during mouse embryonic development and in adult organs. These include the primitive endoderm of the blastocyst, visceral endoderm of the early post-implantation embryo, as well as lateral plate mesoderm, developing heart, liver, lung and gonads. Here, we generate a novel Gata4 targeted allele used to generate both a Gata4H2B-GFP transcriptional reporter and a Gata4FLAG fusion protein to analyse dynamic expression domains. We demonstrate that the Gata4H2B-GFP transcriptional reporter faithfully recapitulates known sites of Gata4 mRNA expression and correlates with endogenous GATA4 protein levels. This reporter labels nuclei of Gata4 expressing cells and is suitable for time-lapse imaging and single cell analyses. As such, this Gata4H2B-GFP allele will be a useful tool for studying Gata4 expression and transcriptional regulation.This article has an associated First Person interview with the first author of the paper.
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In this issue, Metzis et al., demonstrate that in the development of the central nervous system, patterning along the anterior-posterior axis precedes acquisition of neural identity. This contrasts with the prevailing view that neural identity comes first, providing a new window on the origins of the brain and spinal cord.
Subject(s)
Body Patterning , Central Nervous System , Brain , Nervous System , Spinal CordABSTRACT
The FGF/ERK signaling pathway is highly conserved throughout evolution and plays fundamental roles during embryonic development and in adult organisms. While a plethora of expression data exists for ligands, receptors and pathway regulators, we know little about the spatial organization or dynamics of signaling in individual cells within populations. To this end we developed a transcriptional readout of FGF/ERK activity by targeting a histone H2B-linked Venus fluorophore to the endogenous locus of Spry4, an early pathway target, and generated Spry4H2B-Venus embryonic stem cells (ESCs) and a derivative mouse line. The Spry4H2B-Venus reporter was heterogeneously expressed within ESC cultures and responded to FGF/ERK signaling manipulation. In vivo, the Spry4H2B-Venus reporter recapitulated the expression pattern of Spry4 and localized to sites of known FGF/ERK activity including the inner cell mass of the pre-implantation embryo and the limb buds, somites and isthmus of the post-implantation embryo. Additionally, we observed highly localized reporter expression within adult organs. Genetic and chemical disruption of FGF/ERK signaling, in vivo in pre- and post-implantation embryos, abrogated Venus expression establishing the reporter as an accurate signaling readout. This tool will provide new insights into the dynamics of the FGF/ERK signaling pathway during mammalian development.