Predicting chronic postsurgical pain: current evidence and a novel program to develop predictive biomarker signatures

ABSTRACT

Chronic pain affects more than 50 million Americans. Treatments remain inadequate, in large part, because the pathophysiological mechanisms underlying the development of chronic pain remain poorly understood. Pain biomarkers could potentially identify and measure biological pathways and phenotypical expressions that are altered by pain, provide insight into biological treatment targets, and help identify at-risk patients who might benefit from early intervention. Biomarkers are used to diagnose, track, and treat other diseases, but no validated clinical biomarkers exist yet for chronic pain. To address this problem, the National Institutes of Health Common Fund launched the Acute to Chronic Pain Signatures (A2CPS) program to evaluate candidate biomarkers, develop them into biosignatures, and discover novel biomarkers for chronification of pain after surgery. This article discusses candidate biomarkers identified by A2CPS for evaluation, including genomic, proteomic, metabolomic, lipidomic, neuroimaging, psychophysical, psychological, and behavioral measures. Acute to Chronic Pain Signatures will provide the most comprehensive investigation of biomarkers for the transition to chronic postsurgical pain undertaken to date. Data and analytic resources generatedby A2CPS will be shared with the scientific community in hopes that other investigators will extract valuable insights beyond A2CPS's initial findings. This article will review the identified biomarkers and rationale for including them, the current state of the science on biomarkers of the transition from acute to chronic pain, gaps in the literature, and how A2CPS will address these gaps.

The NIH "BEST" programs: Institutional programs, the program evaluation, and early data

Biomedical research training has undergone considerable change over the past several years. At its core, the goal of graduate and postdoctoral training is to provide individuals with the skills and knowledge to become outstanding scientists and expand knowledge through the scientific method. Historically, graduate school training has focused on preparation for academic positions. Increasingly, however, a shift toward preparation for a wider range of career options has emerged. This is largely because most biomedical PhD graduates do not become Principal Investigators in academic laboratories. Here we describe an National Institutes of Health Common Fund program with the major goal of culture change for biomedical research training and training that prepares individuals for a broader expanse of careers in the biomedical research enterprise. These "Broadening Experiences in Scientific Training" (BEST) awards, issued in 2012 and 2013, provided support to institutions to develop innovative approaches to achieving these goals, as a complement to traditional training. Awardees were tasked with catalyzing change at their institutions and sharing best practices across the training community. Awardees were required to participate in a cross-site evaluation that assessed the impact of BEST activities on three main areas: (a) trainee confidence and knowledge to make career decisions, (b) influence of this added activity on time in training, and (c) ability of the institutions to sustain activities deemed to be beneficial. Here we present the fundamental approach to the BEST program and early evaluative data.

FOXD3 Regulates Pluripotent Stem Cell Potential by Simultaneously Initiating and Repressing Enhancer Activity

Early development is governed by the ability of pluripotent cells to retain the full range of developmental potential and respond accurately to developmental cues. This property is achieved in large part by the temporal and contextual regulation of gene expression by enhancers. Here, we evaluated regulation of enhancer activity during differentiation of embryonic stem to epiblast cells and uncovered the forkhead transcription factor FOXD3 as a major regulator of the developmental potential of both pluripotent states. FOXD3 bound to distinct sites in the two cell types priming enhancers through a dual-functional mechanism. It recruited the SWI/SNF chromatin remodeling complex ATPase BRG1 to promote nucleosome removal while concurrently inhibiting maximal activation of the same enhancers by recruiting histone deacetylases1/2. Thus, FOXD3 prepares cognate genes for future maximal expression by establishing and simultaneously repressing enhancer activity. Through switching of target sites, FOXD3 modulates the developmental potential of pluripotent cells as they differentiate.

The origin and implementation of the Broadening Experiences in Scientific Training programs: an NIH common fund initiative

Recent national reports and commentaries on the current status and needs of the U.S. biomedical research workforce have highlighted the limited career development opportunities for predoctoral and postdoctoral trainees in academia, yet little attention is paid to preparation for career pathways outside of the traditional faculty path. Recognizing this issue, in 2013, the U.S. National Institutes of Health (NIH) Common Fund issued a request for application titled "NIH Director's Biomedical Research Workforce Innovation Award: Broadening Experiences in Scientific Training (BEST)." These 5-yr 1-time grants, awarded to 17 single or partnering institutions, were designed to develop sustainable approaches to broaden graduate and postgraduate training, aimed at creating training programs that reflect the range of career options that trainees may ultimately pursue. These institutions have formed a consortium in order to work together to develop, evaluate, share, and disseminate best practices and challenges. This is a first report on the early experiences of the consortium and the scope of participating BEST programs. In this report, we describe the state of the U.S. biomedical workforce and development of the BEST award, variations of programmatic approaches to assist with program design without BEST funding, and novel approaches to engage faculty in career development programs. To test the effectiveness of these BEST programs, external evaluators will assess their outcomes not only over the 5 yr grant period but also for an additional 10 yr beyond award completion.

The NIH Extracellular RNA Communication Consortium

The Extracellular RNA (exRNA) Communication Consortium, funded as an initiative of the NIH Common Fund, represents a consortium of investigators assembled to address the critical issues in the exRNA research arena. The overarching goal is to generate a multi-component community resource for sharing fundamental scientific discoveries, protocols, and innovative tools and technologies. The key initiatives include (a) generating a reference catalogue of exRNAs present in body fluids of normal healthy individuals that would facilitate disease diagnosis and therapies, (b) defining the fundamental principles of exRNA biogenesis, distribution, uptake, and function, as well as development of molecular tools, technologies, and imaging modalities to enable these studies,

Vascular endothelial growth factor coordinates islet innervation via vascular scaffolding

Neurovascular alignment is a common anatomical feature of organs, but the mechanisms leading to this arrangement are incompletely understood. Here, we show that vascular endothelial growth factor (VEGF) signaling profoundly affects both vascularization and innervation of the pancreatic islet. In mature islets, nerves are closely associated with capillaries, but the islet vascularization process during embryonic organogenesis significantly precedes islet innervation. Although a simple neuronal meshwork interconnects the developing islet clusters as they begin to form at E14.5, the substantial ingrowth of nerve fibers into islets occurs postnatally, when islet vascularization is already complete. Using genetic mouse models, we demonstrate that VEGF regulates islet innervation indirectly through its effects on intra-islet endothelial cells. Our data indicate that formation of a VEGF-directed, intra-islet vascular plexus is required for development of islet innervation, and that VEGF-induced islet hypervascularization leads to increased nerve fiber ingrowth. Transcriptome analysis of hypervascularized islets revealed an increased expression of extracellular matrix components and axon guidance molecules, with these transcripts being enriched in the islet-derived endothelial cell population. We propose a mechanism for coordinated neurovascular development within pancreatic islets, in which endocrine cell-derived VEGF directs the patterning of intra-islet capillaries during embryogenesis, forming a scaffold for the postnatal ingrowth of essential autonomic nerve fibers.

Embryonic domains of the aorta derived from diverse origins exhibit distinct properties that converge into a common phenotype in the adult

Vascular smooth muscle cells (VSMCs) are derived from distinct embryonic origins. Vessels originating from differing smooth muscle cell populations have distinct vascular and pathological properties involving calcification, atherosclerosis, and structural defects such as aneurysm and coarctation. We hypothesized that domains within a single vessel, such as the aorta, vary in phenotype based on embryonic origin. Gene profiling and myographic analyses demonstrated that embryonic ascending and descending aortic domains exhibited distinct phenotypes. In vitro analyses demonstrated that VSMCs from each region were dissimilar in terms of cytoskeletal and migratory properties, and retention of different gene expression patterns. Using the same analysis, we found that these same two domains are indistinguishable in the adult vessel. Our data demonstrate that VSMCs from different embryonic origins are functionally distinct in the embryonic mouse, but converge to assume a common phenotype in the aorta of healthy adults. These findings have fundamental implications for aortic development, function and disease progression.

Transcriptional targets of Foxd3 in murine ES cells

Understanding gene regulatory networks controlling properties of pluripotent stem cells will facilitate development of stem cell-based therapies. The transcription factor Foxd3 is critical for maintenance of self-renewal, survival, and pluripotency in murine embryonic stem cells (ESCs). Using a conditional deletion of Foxd3 followed by gene expression analyses, we demonstrate that genes required for several developmental processes including embryonic organ development, epithelium development, and epithelial differentiation were misregulated in the absence of Foxd3. Additionally, we identified 6 novel targets of Foxd3 (Sox4, Safb, Sox15, Fosb, Pmaip1 and Smarcd3). Finally, we present data suggesting that Foxd3 functions upstream of genes required for skeletal muscle development. Together, this work provides further evidence that Foxd3 is a critical regulator of murine development through the regulation of lineage specific differentiation.

A dynamic code of dorsal neural tube genes regulates the segregation between neurogenic and melanogenic neural crest cells

Understanding when and how multipotent progenitors segregate into diverse fates is a key question during embryonic development. The neural crest (NC) is an exemplary model system with which to investigate the dynamics of progenitor cell specification, as it generates a multitude of derivatives. Based on 'in ovo' lineage analysis, we previously suggested an early fate restriction of premigratory trunk NC to generate neural versus melanogenic fates, yet the timing of fate segregation and the underlying mechanisms remained unknown. Analysis of progenitors expressing a Foxd3 reporter reveals that prospective melanoblasts downregulate Foxd3 and have already segregated from neural lineages before emigration. When this downregulation is prevented, late-emigrating avian precursors fail to upregulate the melanogenic markers Mitf and MC/1 and the guidance receptor Ednrb2, generating instead glial cells that express P0 and Fabp. In this context, Foxd3 lies downstream of Snail2 and Sox9, constituting a minimal network upstream of Mitf and Ednrb2 to link melanogenic specification with migration. Consistent with the gain-of-function data in avians, loss of Foxd3 function in mouse NC results in ectopic melanogenesis in the dorsal tube and sensory ganglia. Altogether, Foxd3 is part of a dynamically expressed gene network that is necessary and sufficient to regulate fate decisions in premigratory NC. Their timely downregulation in the dorsal neural tube is thus necessary for the switch between neural and melanocytic phases of NC development.

Ground-state transcriptional requirements for skin-derived precursors

Skin-derived precursors (SKPs) are an attractive stem cell model for cell-based therapies. SKPs can be readily generated from embryonic and adult mice and adult humans, exhibit a high degree of multipotency, and have the potential to serve as a patient autologous stem cell. The advancement of these cells toward therapeutic use depends on the ability to control precisely the self-renewal and differentiation of SKPs. Here we show that two well-known stem cell factors, Foxd3 and Sox2, are critical regulators of the stem cell properties of SKPs. Deletion of Foxd3 completely abolishes the sphere-forming potential of these cells. In the absence of Sox2, SKP spheres can be formed, but with reduced size and frequency. Our results provide entry points into the gene regulatory networks dictating SKP behavior, and pave the way for future studies on a therapeutically relevant stem cell.

Transgenic mouse models

The generation of transgenic mouse models has been a powerful technique for several decades and is still widely used. There have been many manuals and general reviews of this technology. This chapter is designed to be a "how-to" resource with detailed specifics.

Isolation and culture of neural crest cells from embryonic murine neural tube

The embryonic neural crest (NC) is a multipotent progenitor population that originates at the dorsal aspect of the neural tube, undergoes an epithelial to mesenchymal transition (EMT) and migrates throughout the embryo, giving rise to diverse cell types. NC also has the unique ability to influence the differentiation and maturation of target organs. When explanted in vitro, NC progenitors undergo self-renewal, migrate and differentiate into a variety of tissue types including neurons, glia, smooth muscle cells, cartilage and bone. NC multipotency was first described from explants of the avian neural tube. In vitro isolation of NC cells facilitates the study of NC dynamics including proliferation, migration, and multipotency. Further work in the avian and rat systems demonstrated that explanted NC cells retain their NC potential when transplanted back into the embryo. Because these inherent cellular properties are preserved in explanted NC progenitors, the neural tube explant assay provides an attractive option for studying the NC in vitro. To attain a better understanding of the mammalian NC, many methods have been employed to isolate NC populations. NC-derived progenitors can be cultured from post-migratory locations in both the embryo and adult to study the dynamics of post-migratory NC progenitors, however isolation of NC progenitors as they emigrate from the neural tube provides optimal preservation of NC cell potential and migratory properties. Some protocols employ fluorescence activated cell sorting (FACS) to isolate a NC population enriched for particular progenitors. However, when starting with early stage embryos, cell numbers adequate for analyses are difficult to obtain with FACS, complicating the isolation of early NC populations from individual embryos. Here, we describe an approach that does not rely on FACS and results in an approximately 96% pure NC population based on a Wnt1-Cre activated lineage reporter. The method presented here is adapted from protocols optimized for the culture of rat NC. The advantages of this protocol compared to previous methods are that 1) the cells are not grown on a feeder layer, 2) FACS is not required to obtain a relatively pure NC population, 3) premigratory NC cells are isolated and 4) results are easily quantified. Furthermore, this protocol can be used for isolation of NC from any mutant mouse model, facilitating the study of NC characteristics with different genetic manipulations. The limitation of this approach is that the NC is removed from the context of the embryo, which is known to influence the survival, migration and differentiation of the NC.

Enteric nervous system specific deletion of Foxd3 disrupts glial cell differentiation and activates compensatory enteric progenitors

The enteric nervous system (ENS) arises from the coordinated migration, expansion and differentiation of vagal and sacral neural crest progenitor cells. During development, vagal neural crest cells enter the foregut and migrate in a rostro-to-caudal direction, colonizing the entire gastrointestinal tract and generating the majority of the ENS. Sacral neural crest contributes to a subset of enteric ganglia in the hindgut, colonizing the colon in a caudal-to-rostral wave. During this process, enteric neural crest-derived progenitors (ENPs) self-renew and begin expressing markers of neural and glial lineages as they populate the intestine. Our earlier work demonstrated that the transcription factor Foxd3 is required early in neural crest-derived progenitors for self-renewal, multipotency and establishment of multiple neural crest-derived cells and structures including the ENS. Here, we describe Foxd3 expression within the fetal and postnatal intestine: Foxd3 was strongly expressed in ENPs as they colonize the gastrointestinal tract and was progressively restricted to enteric glial cells. Using a novel Ednrb-iCre transgene to delete Foxd3 after vagal neural crest cells migrate into the midgut, we demonstrated a late temporal requirement for Foxd3 during ENS development. Lineage labeling of Ednrb-iCre expressing cells in Foxd3 mutant embryos revealed a reduction of ENPs throughout the gut and loss of Ednrb-iCre lineage cells in the distal colon. Although mutant mice were viable, defects in patterning and distribution of ENPs were associated with reduced proliferation and severe reduction of glial cells derived from the Ednrb-iCre lineage. Analyses of ENS-lineage and differentiation in mutant embryos suggested activation of a compensatory population of Foxd3-positive ENPs that did not express the Ednrb-iCre transgene. Our findings highlight the crucial roles played by Foxd3 during ENS development including progenitor proliferation, neural patterning, and glial differentiation and may help delineate distinct molecular programs controlling vagal versus sacral neural crest development.

Loss of Foxd3 results in decreased β-cell proliferation and glucose intolerance during pregnancy

A complete molecular understanding of β-cell mass expansion will be useful for the improvement of therapies to treat diabetic patients. During normal periods of metabolic challenges, such as pregnancy, β-cells proliferate, or self-renew, to meet the new physiological demands. The transcription factor Forkhead box D3 (Foxd3) is required for maintenance and self-renewal of several diverse progenitor cell lineages, and Foxd3 is expressed in the pancreatic primordium beginning at 10.5 d postcoitum, becoming localized predominantly to β-cells after birth. Here, we show that mice carrying a pancreas-specific deletion of Foxd3 have impaired glucose tolerance, decreased β-cell mass, decreased β-cell proliferation, and decreased β-cell size during pregnancy. In addition, several genes known to regulate proliferation, Foxm1, Skp2, Ezh2, Akt2, and Cdkn1a, are misregulated in islets isolated from these Foxd3 mutant mice. Together, these data place Foxd3 upstream of several pathways critical for β-cell mass expansion in vivo.

Renshaw cell interneuron specialization is controlled by a temporally restricted transcription factor program

The spinal cord contains a diverse array of physiologically distinct interneuron cell types that subserve specialized roles in somatosensory perception and motor control. The mechanisms that generate these specialized interneuronal cell types from multipotential spinal progenitors are not known. In this study, we describe a temporally regulated transcriptional program that controls the differentiation of Renshaw cells (RCs), an anatomically and functionally discrete spinal interneuron subtype. We show that the selective activation of the Onecut transcription factors Oc1 and Oc2 during the first wave of V1 interneuron neurogenesis is a key step in the RC differentiation program. The development of RCs is additionally dependent on the forkhead transcription factor Foxd3, which is more broadly expressed in postmitotic V1 interneurons. Our demonstration that RCs are born, and activate Oc1 and Oc2 expression, in a narrow temporal window leads us to posit that neuronal diversity in the developing spinal cord is established by the composite actions of early spatial and temporal determinants.

A predicted hairpin cluster correlates with barriers to PCR, sequencing and possibly BAC recombineering

Formation of higher-order structure of nucleic acids (hairpins or loops, for example) may impact not only gene regulation, but also molecular biology techniques and approaches critical for design and production of vectors needed for genetic engineering approaches. In the course of designing vectors aimed to modify the murine Foxd3 locus through homologous recombination in embryonic stem cells, we discovered a 370 nucleotide segment of DNA resistant to polymerase read-through. In addition to sequencing and PCR disruptions, we were unable to use BAC recombineering strategies to exchange sequences within the Foxd3 locus. This segment corresponds to a putative DNA hairpin region just upstream of the 5' untranslated region of Foxd3. This region is also highly conserved across vertebrate species, suggesting possible functional significance. Our findings provide a cautionary note for researchers experiencing technical challenges with BAC recombineering or other molecular biology methods requiring recombination or polymerase activity.

Influence and timing of arrival of murine neural crest on pancreatic beta cell development and maturation

Interactions between cells from the ectoderm and mesoderm influence development of the endodermally-derived pancreas. While much is known about how mesoderm regulates pancreatic development, relatively little is understood about how and when the ectodermally-derived neural crest regulates pancreatic development and specifically, beta cell maturation. A previous study demonstrated that signals from the neural crest regulate beta cell proliferation and ultimately, beta cell mass. Here, we expand on that work to describe timing of neural crest arrival at the developing pancreatic bud and extend our knowledge of the non-cell autonomous role for neural crest derivatives in the process of beta cell maturation. We demonstrated that murine neural crest entered the pancreatic mesenchyme between the 26 and 27 somite stages (approximately 10.0 dpc) and became intermingled with pancreatic progenitors as the epithelium branched into the surrounding mesenchyme. Using a neural crest-specific deletion of the Forkhead transcription factor Foxd3, we ablated neural crest cells that migrate to the pancreatic primordium. Consistent with previous data, in the absence of Foxd3, and therefore the absence of neural crest cells, proliferation of insulin-expressing cells and insulin-positive area are increased. Analysis of endocrine cell gene expression in the absence of neural crest demonstrated that, although the number of insulin-expressing cells was increased, beta cell maturation was significantly impaired. Decreased MafA and Pdx1 expression illustrated the defect in beta cell maturation; we discovered that without neural crest, there was a reduction in the percentage of insulin-positive cells that co-expressed Glut2 and Pdx1 compared to controls. In addition, transmission electron microscopy analyses revealed decreased numbers of characteristic insulin granules and the presence of abnormal granules in insulin-expressing cells from mutant embryos. Together, these data demonstrate that the neural crest is a critical regulator of beta cell development on two levels: by negatively regulating beta cell proliferation and by promoting beta cell maturation.

Neural crest stem cell multipotency requires Foxd3 to maintain neural potential and repress mesenchymal fates

Neural crest (NC) progenitors generate a wide array of cell types, yet molecules controlling NC multipotency and self-renewal and factors mediating cell-intrinsic distinctions between multipotent versus fate-restricted progenitors are poorly understood. Our earlier work demonstrated that Foxd3 is required for maintenance of NC progenitors in the embryo. Here, we show that Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. Neural derivatives of NC were lost in Foxd3 mutant mouse embryos, whereas abnormally fated NC-derived vascular smooth muscle cells were ectopically located in the aorta. Cranial NC defects were associated with precocious differentiation towards osteoblast and chondrocyte cell fates, and individual mutant NC from different anteroposterior regions underwent fate changes, losing neural and increasing myofibroblast potential. Our results demonstrate that neural potential can be separated from NC multipotency by the action of a single gene, and establish novel parallels between NC and other progenitor populations that depend on this functionally conserved stem cell protein to regulate self-renewal and multipotency.

Functional interaction between Foxd3 and Pax3 in cardiac neural crest development

The transcription factors Foxd3 and Pax3 are important early regulators of neural crest (NC) progenitor cell properties. Homozygous mutations of Pax3 or a homozygous NC-specific deletion of Foxd3 cause marked defects in most NC derivatives, but neither loss of both Foxd3 alleles nor loss of one Pax3 allele alone greatly affects overall development of cardiac NC derivatives. In contrast, compound mutant embryos homozygous for a NC-specific Foxd3 mutation and heterozygous for Pax3 have fully penetrant persistent truncus arteriosus, severe thymus hypoplasia, and midgestation lethality. Foxd3; Pax3 compound mutant embryos have increased cell death in the neural folds and a drastic early reduction of NC cells, with an almost complete absence of NC caudal to the first pharyngeal arch. The genetic interaction between these genes implicates gene dosage-sensitive roles for Foxd3 and Pax3 in cardiac NC progenitors. Foxd3 and Pax3 act together to affect survival and maintenance of cardiac NC progenitors, and loss of these progenitors catastrophically affects key aspects of later cardiovascular development.

Conditional gene targeting in mouse pancreatic ß-Cells: analysis of ectopic Cre transgene expression in the brain

OBJECTIVE

Conditional gene targeting has been extensively used for in vivo analysis of gene function in β-cell biology. The objective of this study was to examine whether mouse transgenic Cre lines, used to mediate β-cell- or pancreas-specific recombination, also drive Cre expression in the brain.

RESEARCH DESIGN AND METHODS

Transgenic Cre lines driven by Ins1, Ins2, and Pdx1 promoters were bred to R26R reporter strains. Cre activity was assessed by β-galactosidase or yellow fluorescent protein expression in the pancreas and the brain. Endogenous Pdx1 gene expression was monitored using Pdx1(tm1Cvw) lacZ knock-in mice. Cre expression in β-cells and co-localization of Cre activity with orexin-expressing and leptin-responsive neurons within the brain was assessed by immunohistochemistry.

RESULTS

All transgenic Cre lines examined that used the Ins2 promoter to drive Cre expression showed widespread Cre activity in the brain, whereas Cre lines that used Pdx1 promoter fragments showed more restricted Cre activity primarily within the hypothalamus. Immunohistochemical analysis of the hypothalamus from Tg(Pdx1-cre)(89.1Dam) mice revealed Cre activity in neurons expressing orexin and in neurons activated by leptin. Tg(Ins1-Cre/ERT)(1Lphi) mice were the only line that lacked Cre activity in the brain.

CONCLUSIONS

Cre-mediated gene manipulation using transgenic lines that express Cre under the control of the Ins2 and Pdx1 promoters are likely to alter gene expression in nutrient-sensing neurons. Therefore, data arising from the use of these transgenic Cre lines must be interpreted carefully to assess whether the resultant phenotype is solely attributable to alterations in the islet β-cells.

Epigenetic priming of a pre-B cell-specific enhancer through binding of Sox2 and Foxd3 at the ESC stage

Modifications to the core histones are thought to contribute to ESC pluripotency by priming tissue-specific promoters and enhancers for later activation. However, it is unclear how these marks are targeted in ESCs and maintained during differentiation. Here, we show that the ESC factor Sox2 targets H3K4 methylation to monovalent and bivalent domains. In ESCs, Sox2 contributes to the formation of a monovalent mark at an enhancer in the pro/pre-B cell-specific lambda5-VpreB1 locus. Binding of Foxd3 suppresses intergenic transcription of the enhancer and surrounding sequences. In pro-B cells, enhancer activity is dependent on the Sox and Fox binding sites, and the enhancer is bound by Sox4, which is required for efficient expression of lambda5. Our results lead us to propose a factor relay model whereby ESC factors establish active epigenetic marks at tissue specific elements before being replaced by cell type-specific factors as cells differentiate.

Identification of Arx transcriptional targets in the developing basal forebrain

Mutations in the aristaless-related homeobox (ARX) gene are associated with multiple neurologic disorders in humans. Studies in mice indicate Arx plays a role in neuronal progenitor proliferation and development of the cerebral cortex, thalamus, hippocampus, striatum, and olfactory bulbs. Specific defects associated with Arx loss of function include abnormal interneuron migration and subtype differentiation. How disruptions in ARX result in human disease and how loss of Arx in mice results in these phenotypes remains poorly understood. To gain insight into the biological functions of Arx, we performed a genome-wide expression screen to identify transcriptional changes within the subpallium in the absence of Arx. We have identified 84 genes whose expression was dysregulated in the absence of Arx. This population was enriched in genes involved in cell migration, axonal guidance, neurogenesis, and regulation of transcription and includes genes implicated in autism, epilepsy, and mental retardation; all features recognized in patients with ARX mutations. Additionally, we found Arx directly repressed three of the identified transcription factors: Lmo1, Ebf3 and Shox2. To further understand how the identified genes are involved in neural development, we used gene set enrichment algorithms to compare the Arx gene regulatory network (GRN) to the Dlx1/2 GRN and interneuron transcriptome. These analyses identified a subset of genes in the Arx GRN that are shared with that of the Dlx1/2 GRN and that are enriched in the interneuron transcriptome. These data indicate Arx plays multiple roles in forebrain development, both dependent and independent of Dlx1/2, and thus provides further insights into the understanding of the mechanisms underlying the pathology of mental retardation and epilepsy phenotypes resulting from ARX mutations.

Regulation of embryonic stem cell self-renewal and pluripotency by Foxd3

The Foxd3 forkhead transcription factor is required for maintaining pluripotent cells in the early mouse embryo and for the establishment of murine embryonic stem cell (ESC) lines. To begin to understand the role of Foxd3 in ESC maintenance, we derived ESC lines from blastocysts that carried two conditional Foxd3 alleles and a tamoxifen-inducible Cre transgene. Tamoxifen treatment produced a rapid and near complete loss of Foxd3 mRNA and protein. Foxd3-deficient ESCs maintained a normal proliferation rate but displayed increased apoptosis, and clonally dispersed ESCs showed a decreased ability to self-renew. Under either self-renewal or differentiation-promoting culture conditions we observed a strong, precocious differentiation of Foxd3 mutant ESCs along multiple lineages, including trophectoderm, endoderm, and mesendoderm. This profound alteration in biological behavior occurred in the face of continued expression of factors known to induce pluripotency, including Oct4, Sox2, and Nanog. We present a model for the role of Foxd3 in repressing differentiation, promoting self-renewal, and maintaining survival of mouse ESCs. Disclosure of potential conflicts of interest is found at the end of this article.

Requirement for Foxd3 in the maintenance of neural crest progenitors

Understanding the molecular mechanisms of stem cell maintenance is crucial for the ultimate goal of manipulating stem cells for the treatment of disease. Foxd3 is required early in mouse embryogenesis; Foxd3(-/-) embryos fail around the time of implantation, cells of the inner cell mass cannot be maintained in vitro, and blastocyst-derived stem cell lines cannot be established. Here, we report that Foxd3 is required for maintenance of the multipotent mammalian neural crest. Using tissue-specific deletion of Foxd3 in the neural crest, we show that Foxd3(flox/-); Wnt1-Cre mice die perinatally with a catastrophic loss of neural crest-derived structures. Cranial neural crest tissues are either missing or severely reduced in size, the peripheral nervous system consists of reduced dorsal root ganglia and cranial nerves, and the entire gastrointestinal tract is devoid of neural crest derivatives. These results demonstrate a global role for this transcriptional repressor in all aspects of neural crest maintenance along the anterior-posterior axis, and establish an unprecedented molecular link between multiple divergent progenitor lineages of the mammalian embryo.

A viable mouse model of factor X deficiency provides evidence for maternal transfer of factor X

BACKGROUND

Activated factor X (FXa) is a vitamin K-dependent serine protease that plays a pivotal role in blood coagulation by converting prothrombin to thrombin. There are no reports of humans with complete deficiency of FX, and knockout of murine F10 is embryonic or perinatal lethal.

OBJECTIVE

We sought to generate a viable mouse model of FX deficiency.

METHODS

We used a socket-targeting construct to generate F10-knockout mice by eliminating F10 exon 8 (knockout allele termed F10(tm1Ccmt), abbreviated as '-'; wild-type '+'), and a plug-targeting construct to generate mice expressing a FX variant with normal antigen levels but low levels of FX activity [4-9% normal in humans carrying the defect, Pro343-->Ser, termed FX Friuli (mutant allele termed F10(tm2Ccmt), abbreviated as F)].

RESULTS

F10 knockout mice exhibited embryonic or perinatal lethality. In contrast, homozygous Friuli mice [F10 (F/F)] had FX activity levels of approximately 5.5% (sufficient to rescue both embryonic and perinatal lethality), but developed age-dependent iron deposition and cardiac fibrosis. Interestingly, F10 (-/F) mice with FX activity levels of 1-3% also showed complete rescue of lethality. Further study of this model provides evidence supporting a role of maternal FX transfer in the embryonic survival.

CONCLUSIONS

We demonstrate that, while complete absence of FX is incompatible with murine survival, minimal FX activity as low as 1-3% is sufficient to rescue the lethal phenotype. This viable low-FX mouse model will facilitate the development of FX-directed therapies as well as investigation of the FX role in embryonic development.

SULF1 and SULF2 regulate heparan sulfate-mediated GDNF signaling for esophageal innervation

Heparan sulfate (HS) plays an essential role in extracellular signaling during development. Biochemical studies have established that HS binding to ligands and receptors is regulated by the fine 6-O-sulfated structure of HS; however, mechanisms that control sulfated HS structure and associated signaling functions in vivo are not known. Extracellular HS 6-O-endosulfatases, SULF1 and SULF2, are candidate enzymatic regulators of HS 6-O-sulfated structure and modulate HS-dependent signaling. To investigate Sulf regulation of developmental signaling, we have disrupted Sulf genes in mouse and identified redundant functions of Sulfs in GDNF-dependent neural innervation and enteric glial formation in the esophagus, resulting in esophageal contractile malfunction in Sulf1(-/-);Sulf2(-/-) mice. SULF1 is expressed in GDNF-expressing esophageal muscle and SULF2 in innervating neurons, establishing their direct functions in esophageal innervation. Biochemical and cell signaling studies show that Sulfs are the major regulators of HS 6-O-desulfation, acting to reduce GDNF binding to HS and to enhance GDNF signaling and neurite sprouting in the embryonic esophagus. The functional specificity of Sulfs in GDNF signaling during esophageal innervation was established by showing that the neurite sprouting is selectively dependent on GDNF, but not on neurotrophins or other signaling ligands. These findings provide the first in vivo evidence that Sulfs are essential developmental regulators of cellular HS 6-O-sulfation for matrix transmission and reception of GDNF signal from muscle to innervating neurons.

A viable mouse model of factor X deficiency provides evidence for maternal transfer of factor X

BACKGROUND

Activated factor X (FXa) is a vitamin K-dependent serine protease that plays a pivotal role in blood coagulation by converting prothrombin to thrombin. There are no reports of humans with complete deficiency of FX, and knockout of murine F10 is embryonic or perinatal lethal.

OBJECTIVE

We sought to generate a viable mouse model of FX deficiency.

METHODS

We used a socket-targeting construct to generate F10-knockout mice by eliminating F10 exon 8 (knockout allele termed F10(tm1Ccmt), abbreviated as '-'; wild-type '+'), and a plug-targeting construct to generate mice expressing a FX variant with normal antigen levels but low levels of FX activity [4-9% normal in humans carrying the defect, Pro343-->Ser, termed FX Friuli (mutant allele termed F10(tm2Ccmt), abbreviated as F)].

RESULTS

F10 knockout mice exhibited embryonic or perinatal lethality. In contrast, homozygous Friuli mice [F10 (F/F)] had FX activity levels of approximately 5.5% (sufficient to rescue both embryonic and perinatal lethality), but developed age-dependent iron deposition and cardiac fibrosis. Interestingly, F10 (-/F) mice with FX activity levels of 1-3% also showed complete rescue of lethality. Further study of this model provides evidence supporting a role of maternal FX transfer in the embryonic survival.

CONCLUSIONS

We demonstrate that, while complete absence of FX is incompatible with murine survival, minimal FX activity as low as 1-3% is sufficient to rescue the lethal phenotype. This viable low-FX mouse model will facilitate the development of FX-directed therapies as well as investigation of the FX role in embryonic development.

Embryonic germ cell lines and their derivation from mouse primordial germ cells

When primordial germ cells of the mouse are cultured on feeder layers with the addition of the polypeptide signalling molecules leukaemia inhibitory factor, Steel factor and basic fibroblast growth factor they give rise to cells that resemble undifferentiated blastocyst-derived embryonic stem cells. These primordial germ cell-derived embryonic germ cells (EG cells) can be induced to differentiate extensively in culture and also form teratocarcinomas when injected into nude mice. Additionally, they contribute to chimeras when injected into host blastocysts. We have derived multiple EG cell lines from 8.5 days post coitum (dpc) embryos of C57BL/6 inbred mice. Four independent EG cell lines with normal male karyotypes have formed chimeras (up to 70% coat colour chimerism) when injected into BALB/c host blastocysts. Chimeric mice from all four cell lines are fertile, but only those from one line have transmitted coat colour markers through the germline. Studies have also been carried out to determine whether gonadal primordial germ cells can give rise to pluripotent EG cells. Germ cells from gonads of 15.5 dpc C57BL/6 embryos and newborn mice failed to produce EG cell lines. EG cell lines capable of forming teratocarcinomas and coat colour chimeras have been established from primordial germ cells of 12.5 dpc genital ridges. We are currently testing the genomic imprinting status of the insulin-like growth factor type 2 receptor gene (Igf2r) in our different EG cell lines.

Resident endothelial precursors in muscle, adipose, and dermis contribute to postnatal vasculogenesis

A novel population of tissue-resident endothelial precursors (TEPs) was isolated from small blood vessels in dermal, adipose, and skeletal muscle of mouse based on their ability to be grown as spheres. Cellular and molecular analyses of these cells revealed that they were highly related regardless of the tissue of origin and distinct from embryonic neural stem cells. Notably, TEPs did not express hematopoietic markers, but they expressed numerous characteristics of angiogenic precursors and their differentiated progeny, such as CD34, Flk-1, Tie-1, CD31, and vascular endothelial cadherin (VE-cadherin). TEPs readily differentiated into endothelial cells in newly formed vascular networks following transplantation into regenerating skeletal muscle. Taken together, these experiments suggest that TEPs represent a novel class of endothelial precursors that are closely associated with small blood vessels in muscle, adipose, and dermal tissue. This finding is of particular interest since it could bring new insight in cancer angiogenesis and collateral blood vessels developed following ischemia. Disclosure of potential conflicts of interest is found at the end of this article.

Neural Crest Stem Cells

Stem cells are defined by their ability to both self-renew and give rise to multiple lineages in vivo and/or in vitro. As discussed in other chapters in this volume, the embryonic neural crest is a multipotent tissue that gives rise to a plethora of differentiated cell types in the adult organism and is unique to vertebrate embryos. From the point of view of stem cell biology, the neural crest is an ideal source for multipotent adult stem cells. Significant advances have been made in the past few years isolating neural crest stem cell lines that can be maintained in vitro and can give rise to many neural crest derivatives either in vitro or when placed back into the context of an embryo. The initial work identifying these stem cells was carried out with premigratory neural crest from the embryonic neural tube. Later, neural crest stem cells were isolated from postmigratory neural crest, presumably more restricted in developmental potential. More recently it has been demonstrated that neural crest stem cell progenitors persist in the adult in at least two differentiated tissues, the enteric nervous system of the gut and the whisker follicles of the facial skin. In all cases, the properties of the stem cells derived reflect their tissue of origin and the potential of the progenitors becomes more restricted with age. In this chapter we will review this work and speculate on future possibilities with respect to combining our knowledge of neural crest gene function in the embryo and the manipulation of adult neural crest stem cells in vitro and eventually in vivo.

FoxD3 regulation of Nodal in the Spemann organizer is essential for Xenopus dorsal mesoderm development

Induction and patterning of the mesodermal germ layer is a key early step of vertebrate embryogenesis. We report that FoxD3 function in the Xenopus gastrula is essential for dorsal mesodermal development and for Nodal expression in the Spemann organizer. In embryos and explants, FoxD3 induced mesodermal genes, convergent extension movements and differentiation of axial tissues. Engrailed-FoxD3, but not VP16-FoxD3, was identical to native FoxD3 in mesoderm-inducing activity, indicating that FoxD3 functions as a transcriptional repressor to induce mesoderm. Antagonism of FoxD3 with VP16-FoxD3 or morpholino-knockdown of FoxD3 protein resulted in a complete block to axis formation, a loss of mesodermal gene expression, and an absence of axial mesoderm, indicating that transcriptional repression by FoxD3 is required for mesodermal development. FoxD3 induced mesoderm in a non-cell-autonomous manner, indicating a role for secreted inducing factors in the response to FoxD3. Consistent with this mechanism, FoxD3 was necessary and sufficient for the expression of multiple Nodal-related genes, and inhibitors of Nodal signaling blocked mesoderm induction by FoxD3. Therefore, FoxD3 is required for Nodal expression in the Spemann organizer and this function is essential for dorsal mesoderm formation.

Expression and shifting subcellular localization of the transcription factor, Foxd3, in embryonic and adult pancreas

Multipotent progenitor cells self renew throughout an animal's lifetime and can differentiate to give rise to different cell types. Before we can fully understand the developmental potential of progenitor cells and control their differentiation both in vivo and in vitro as stem cells, identification and characterization of the genes that control stem cell fate must first be obtained. Foxd3, a member of the forkhead family of transcriptional regulators, is required for the maintenance of embryonic stem cells and trophoblast stem cells of the early mouse embryo. We describe here the expression of this protein in the developing pancreas. Foxd3 is expressed in most beta cells and infrequently in alpha and PP cells but is not expressed in somatostatin cells. The subcellular localization of Foxd3 varies with fat content in the diet; with a high fat diet the protein is found primarily in the cytoplasm while a low fat diet results in nuclear localization. Foxd3 is differentially localized in a rat model of diabetes: it is nuclear in ZDF rats but cytoplasmic in their lean counterparts. Foxd3 is nuclear in Lep(Ob/Ob) mice.

HIF-2alpha regulates Oct-4: effects of hypoxia on stem cell function, embryonic development, and tumor growth

The division, differentiation, and function of stem cells and multipotent progenitors are influenced by complex signals in the microenvironment, including oxygen availability. Using a genetic "knock-in" strategy, we demonstrate that targeted replacement of the oxygen-regulated transcription factor HIF-1alpha with HIF-2alpha results in expanded expression of HIF-2alpha-specific target genes including Oct-4, a transcription factor essential for maintaining stem cell pluripotency. We show that HIF-2alpha, but not HIF-1alpha, binds to the Oct-4 promoter and induces Oct-4 expression and transcriptional activity, thereby contributing to impaired development in homozygous Hif-2alpha KI/KI embryos, defective hematopoietic stem cell differentiation in embryoid bodies, and large embryonic stem cell (ES)-derived tumors characterized by altered cellular differentiation. Furthermore, loss of HIF-2alpha severely reduces the number of embryonic primordial germ cells, which require Oct-4 expression for survival and/or maintenance. These results identify Oct-4 as a HIF-2alpha-specific target gene and indicate that HIF-2alpha can regulate stem cell function and/or differentiation through activation of Oct-4, which in turn contributes to HIF-2alpha's tumor promoting activity.

Foxd3 is required in the trophoblast progenitor cell lineage of the mouse embryo

The murine blastocyst contains two nonoverlapping pools of progenitor cells: the embryonic component contributes to the fetus and generates embryonic stem cells in vitro, whereas the extraembryonic pool contributes to the placenta and generates trophoblast stem cells in vitro. The transcriptional repressor Foxd3 is required for maintenance of the epiblast and the in vitro establishment of embryonic stem cell lines. Here, we demonstrate that Foxd3 is also required in the trophoblast lineage. Trophoblast progenitors in Foxd3-/- embryos do not self-renew and are not multipotent, but instead give rise to an excess of trophoblast giant cells. Injection of Foxd3-/- blastocysts with wild type ES cells fails to rescue Foxd3-/- placentas and such chimeras die around 10 days of embryogenesis. These results indicate an essential role for Foxd3 in two nonoverlapping progenitor cell populations that require different secreted factors to maintain their multipotent properties in vitro and give rise to divergent tissues in vivo. Moreover, this provides support for the hypothesis that there are conserved molecular mechanisms for maintaining the self-renewing properties of diverse progenitor cell types.

Electroporation of murine embryonic stem cells: a step-by-step guide

The manipulation of embryonic stem (ES) cells to generate targeted mutations via homologous recombination has proved an invaluable resource for researchers from fields as diverse as embryology, immunology, physiology, and biophysics. The derivation and culture of these cells has been described in many places, but there is no substitute for hands-on experience. In lieu of that, here we provide a step-by-step guide for the technique of electroporation, complete with micrographs of the cells at each step of the process. This is intended to allow the first time ES cell worker, as well as the more experienced researcher, to view the morphology of ES cells under ideal conditions as well as when the cells are suboptimal and should be discarded.

A dermal niche for multipotent adult skin-derived precursor cells

A fundamental question in stem cell research is whether cultured multipotent adult stem cells represent endogenous multipotent precursor cells. Here we address this question, focusing on SKPs, a cultured adult stem cell from the dermis that generates both neural and mesodermal progeny. We show that SKPs derive from endogenous adult dermal precursors that exhibit properties similar to embryonic neural-crest stem cells. We demonstrate that these endogenous SKPs can first be isolated from skin during embryogenesis and that they persist into adulthood, with a niche in the papillae of hair and whisker follicles. Furthermore, lineage analysis indicates that both hair and whisker follicle dermal papillae contain neural-crest-derived cells, and that SKPs from the whisker pad are of neural-crest origin. We propose that SKPs represent an endogenous embryonic precursor cell that arises in peripheral tissues such as skin during development and maintains multipotency into adulthood.

Requirement for Foxd3 in maintaining pluripotent cells of the early mouse embryo

Critical to our understanding of the developmental potential of stem cells and subsequent control of their differentiation in vitro and in vivo is a thorough understanding of the genes that control stem cell fate. Here, we report that Foxd3, a member of the forkhead family of transcriptional regulators, is required for maintenance of embryonic cells of the early mouse embryo. Foxd3-/- embryos die after implantation at approximately 6.5 days postcoitum with a loss of epiblast cells, expansion of proximal extraembryonic tissues, and a distal, mislocalized anterior organizing center. Moreover, it has not been possible to establish Foxd3-/- ES cell lines or to generate Foxd3-/- teratocarcinomas. Chimera analysis reveals that Foxd3 function is required in the epiblast and that Foxd3-/- embryos can be rescued by a small number of wild-type cells. Foxd3-/- mutant blastocysts appear morphologically normal and express Oct4, Sox2, and Fgf4, but when placed in vitro the inner cell mass initially proliferates and then fails to expand even when Fgf4 is added. These results establish Foxd3 as a factor required for the maintenance of progenitor cells in the mammalian embryo.

The zinc-finger transcription factor Klf4 is required for terminal differentiation of goblet cells in the colon

Klf4 (formerly GKLF) is a zinc-finger transcription factor expressed in the epithelia of the skin, lungs, gastrointestinal tract and several other organs. In vitro studies have suggested that Klf4 plays an important role in cell proliferation and/or differentiation. Mice homozygous for a null mutation in Klf4 die within 15 hours of birth and show selective perturbation of late-stage differentiation structures in the epidermis, but the function of Klf4 in the gastrointestinal tract has not been investigated. To address this issue, we have generated Klf4(-/-) mice by homologous recombination in embryonic stem cells. In this study, we provide the first in vivo evidence that Klf4 is a goblet cell-specific differentiation factor in the colon. Klf4(-/-) mice exhibit normal cell proliferation and cell death rates in the colon on postnatal day 1. However, Klf4(-/-) mice demonstrate a 90% decrease in the number of goblet cells in the colon, show abnormal expression of the goblet cell-specific marker Muc2 by in situ hybridization, have abnormal staining of the colonic epithelium with Alcian Blue for acidic mucins, and lack normal goblet cell morphology by ultrastructural analysis. All other epithelial cell types are present in the colon of Klf4(-/-) mice. In summary, Klf4 plays a crucial role in colonic epithelial cell differentiation in vivo.

The winged helix gene, Foxb1, controls development of mammary glands and regions of the CNS that regulate the milk-ejection reflex

The ability to lactate is a process restricted to mammals and is necessary for the survival of nonhuman mammals. Female mice carrying a null mutation in the winged helix transcription factor Foxb1 (previously Mf3/Fkh5/TWH) have lactation defects on inbred genetic backgrounds. To determine the cellular basis of the Foxb1 lactation defect we have inserted a tau-lacZ lineage marker into the locus to follow the fate of Foxb1 expressing cells. This approach has revealed that Foxb1 is expressed in epithelial cells of developing and adult mammary glands as well as previously described regions of the central nervous system. Mammary glands from C57BL/6 Foxb1-/- mice have incomplete lobuloalveolar development. In addition, the tau-lacZ lineage label was used to determine that the mammillothalamic tract was lost in all Foxb1-/- mice. Finally, morphological defects in the inferior colliculi of the midbrain in Foxb1-/- mice correlate with the inability to lactate, suggesting that the midbrain defect, but not the loss of the mammillothalamic tract, may be responsible for the lactation defect.

Mesendoderm induction and reversal of left-right pattern by mouse Gdf1, a Vg1-related gene

TGFbeta signals play important roles in establishing the body axes and germ layers in the vertebrate embryo. Vg1 is a TGFbeta-related gene that, due to its maternal expression and vegetal localization in Xenopus, has received close examination as a potential regulator of development in Xenopus, zebrafish, and chick. However, a mammalian Vg1 ortholog has not been identified. To isolate mammalian Vg1 we screened a mouse expression library with a Vg1-specific monoclonal antibody and identified a single cross-reactive clone encoding mouse Gdf1. Gdf1 is expressed uniformly throughout the embryonic region at 5.5-6.5 days postcoitum and later in the node, midbrain, spinal cord, paraxial mesoderm, lateral plate mesoderm, and limb bud. When expressed in Xenopus embryos, native GDF1 is not processed, similar to Vg1. In contrast, a chimeric protein containing the prodomain of Xenopus BMP2 fused to the GDF1 mature domain is efficiently processed and signals via Smad2 to induce mesendoderm and axial duplication. Finally, right-sided expression of chimeric GDF1, but not native GDF1, reverses laterality and results in right-sided Xnr1 expression and reversal of intestinal and heart looping. Therefore, GDF1 can regulate left-right patterning, consistent with the Gdf1 loss-of-function analysis in the mouse (C. T. Rankin, T. Bunton, A. M. Lawler, and S. J. Lee, 2000, Nature Genet. 24, 262-265) and a proposed role for Vg1 in Xenopus. Our results establish that Gdf1 is posttranslationally regulated, that mature GDF1 activates a Smad2-dependent signaling pathway, and that mature GDF1 is sufficient to reverse the left-right axis. Moreover, these findings demonstrate that GDF1 and Vg1 are equivalent in biochemical and functional assays, suggesting that Gdf1 provides a Vg1-like function in the mammalian embryo.

BMP signaling is essential for development of skeletogenic and neurogenic cranial neural crest

BMP signaling is essential for a wide variety of developmental processes. To evaluate the role of Bmp2/4 in cranial neural crest (CNC) formation or differentiation after its migration into the branchial arches, we used Xnoggin to block their activities in specific areas of the CNC in transgenic mice. This resulted in depletion of CNC cells from the targeted areas. As a consequence, the branchial arches normally populated by the affected neural crest cells were hypomorphic and their skeletal and neural derivatives failed to develop. In further analyses, we have identified Bmp2 as the factor required for production of migratory cranial neural crest. Its spatial and temporal expression patterns mirror CNC emergence and Bmp2 mutant embryos lack both branchial arches and detectable migratory CNC cells. Our results provide functional evidence for an essential role of BMP signaling in CNC development.