The neural crest stem cells: control of neural crest cell fate and plasticity by endothelin-3

News from the endothelin-3/EDNRB signaling pathway: Role during enteric nervous system development and involvement in neural crest-associated disorders

The endothelin system is a vertebrate-specific innovation with important roles in regulating the cardiovascular system and renal and pulmonary processes, as well as the development of the vertebrate-specific neural crest cell population and its derivatives. This system is comprised of three structurally similar 21-amino acid peptides that bind and activate two G-protein coupled receptors. In 1994, knockouts of the Edn3 and Ednrb genes revealed their crucial function during development of the enteric nervous system and melanocytes, two neural-crest derivatives. Since then, human and mouse genetics, combined with cellular and developmental studies, have helped to unravel the role of this signaling pathway during development and adulthood. In this review, we will summarize the known functions of the EDN3/EDNRB pathway during neural crest development, with a specific focus on recent scientific advances, and the enteric nervous system in normal and pathological conditions.

Connecting teratogen-induced congenital heart defects to neural crest cells and their effect on cardiac function

Neural crest cells play many key roles in embryonic development, as demonstrated by the abnormalities that result from their specific absence or dysfunction. Unfortunately, these key cells are particularly sensitive to abnormalities in various intrinsic and extrinsic factors, such as genetic deletions or ethanol-exposure that lead to morbidity and mortality for organisms. This review discusses the role identified for a segment of neural crest in regulating the morphogenesis of the heart and associated great vessels. The paradox is that their derivatives constitute a small proportion of cells to the cardiovascular system. Findings supporting that these cells impact early cardiac function raises the interesting possibility that they indirectly control cardiovascular development at least partially through regulating function. Making connections between insults to the neural crest, cardiac function, and morphogenesis is more approachable with technological advances. Expanding our understanding of early functional consequences could be useful in improving diagnosis and testing therapies.

Production of chick embryo extract for the cultivation of murine neural crest stem cells

The neural crest arises from the neuro-ectoderm during embryogenesis and persists only temporarily. Early experiments already proofed pluripotent progenitor cells to be an integral part of the neural crest(1). Phenotypically, neural crest stem cells (NCSC) are defined by simultaneously expressing p75 (low-affine nerve growth factor receptor, LNGFR) and SOX10 during their migration from the neural crest(2,3,4,5). These progenitor cells can differentiate into smooth muscle cells, chromaffin cells, neurons and glial cells, as well as melanocytes, cartilage and bone(6,7,8,9). To cultivate NCSC in vitro, a special neural crest stem cell medium (NCSCM) is required(10). The most complex part of the NCSCM is the preparation of chick embryo extract (CEE) representing an essential source of growth factors for the NCSC as well as for other types of neural explants. Other NCSCM ingredients beside CEE are commercially available. Producing CCE using laboratory standard equipment it is of high importance to know about the challenging details as the isolation, maceration, centrifugation, and filtration processes. In this protocol we describe accurate techniques to produce a maximized amount of pure and high quality CEE.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

Potential neural progenitor cells in fetal liver and regenerating liver

From unfractionated embryonic mice liver cells, appreciable amount of spherical bodies containing nestin-positive cells were generated in the presence of neuronal growth factors. Following cultivation on poly-D: -lysine/laminin-coated slips, approximately 70% of the cells expressed neuronal markers, and 16% had long processes. Functional analysis of these long-process-bearing cells with the whole-cell patch clamp method showed an inward current in response to glutamate, GABA, and serotonin as the neuronal characteristics. Furthermore, regenerating liver in adult mice also contained nestin-positive cells to the same extent as fetal liver. Regenerating liver could have potential as a source of neural cells for autologous transplantation.

The ovarian endothelin network: an evolving story

The endothelin (ET) system consists of three ET isopeptides, several converting enzyme isoforms and two G-protein-coupled receptors, ETA and ETB, which are linked to multiple signaling pathways. Less than 20 years after the initial detection of ET-1 in granulosa cells, the ovarian ET network continues to expand with the discovery of new members and functions. ETs influence a broad range of essential reproductive processes, such as ovulation, steroidogenesis and luteolysis. Therefore, a more comprehensive understanding of the ovarian ET network might provide new strategies for controlling reproduction. This review presents up-to-date findings on the ET network in the ovary.

Establishment and controlled differentiation of neural crest stem cell lines using conditional transgenesis

Murine neural crest stem cells (NCSCs) are a multipotent transient population of stem cells. After being formed during early embryogenesis as a consequence of neurulation at the apical neural fold, the cells rapidly disperse throughout the embryo, migrating along specific pathways and differentiating into a wide variety of cell types. In vitro the multipotency is lost rapidly, making it difficult to study differentiation potential as well as cell fate decisions. Using a transgenic mouse line, allowing for spatio-temporal control of the transforming c-myc oncogene, we derived a cell line (JoMa1), which expressed NCSC markers in a transgene-activity dependent manner. JoMa1 cells express early NCSC markers and can be instructed to differentiate into neurons, glia, smooth muscle cells, melanocytes, and also chondrocytes. A cell-line, clonally derived from JoMa1 culture, termed JoMa1.3 showed identical behavior and was studied in more detail. This system therefore represents a powerful tool to study NCSC biology and signaling pathways. We observed that when proliferative and differentiation stimuli were given, enhanced cell death could be detected, suggesting that the two signals are incompatible in the cellular context. However, the cells regain their differentiation potential after inactivation of c-MycER(T). In summary, we have established a system, which allows for the biochemical analysis of the molecular pathways governing NCSC biology. In addition, we should be able to obtain NCSC lines from crossing the c-MycER(T) mice with mice harboring mutations affecting neural crest development enabling further insight into genetic pathways controlling neural crest differentiation.

The genetic and molecular bases of monogenic disorders affecting proteolytic systems

Complete and limited proteolysis represents key events that regulate many biological processes. At least 5% of the human genome codes for components of proteolytic processes if proteases, inhibitors, and cofactors are taken into account. Accordingly, disruption of proteolysis is involved in numerous pathological conditions. In particular, molecular genetic studies have identified a growing number of monogenic disorders caused by mutations in protease coding genes, highlighting the importance of this class of enzymes in development, organogenesis, immunity, and brain function. This review provides insights into the current knowledge about the molecular genetic causes of these disorders. It should be noted that most are due to loss of function mutations, indicating absolute requirement of proteolytic activities for normal cellular functions. Recent progress in understanding the function of the implicated proteins and the disease pathogenesis is detailed. In addition to providing important clues to the diagnosis, treatment, and pathophysiology of disease, functional characterisation of mutations in proteolytic systems emphasises the pleiotropic functions of proteases in the body homeostasis.

Maintenance of mammalian enteric nervous system progenitors by SOX10 and endothelin 3 signalling

The transcriptional regulator SOX10 and the signalling molecule endothelin 3 have important roles in the development of the mammalian enteric nervous system (ENS). Using a clonal cell culture system, we show that SOX10 inhibits overt neuronal and glial differentiation of multilineage ENS progenitor cells (EPCs), without interfering with their neurogenic commitment. We also demonstrate that endothelin 3 inhibits reversibly the commitment and differentiation of EPCs along the neurogenic and gliogenic lineages, suggesting a role for this factor in the maintenance of multilineage ENS progenitors. Consistent with such a role, the proportion of Sox10-expressing progenitors in the total population of enteric neural crest cells is reduced in the gut of endothelin 3-deficient embryos. This reduction may be related to the requirement of endothelin signalling for the proliferation of ENS progenitors. The dependence of ENS progenitors on endothelin 3 is more pronounced at the migratory front of enteric neural crest cells, which is associated with relatively high levels of endothelin 3 mRNA. Our findings indicate that SOX10 and endothelin 3 have a crucial role in the maintenance of multilineage enteric nervous system progenitors.

Exogenous and Fibroblast Growth Factor 2/Epidermal Growth Factor-Regulated Endogenous Cytokines Regulate Neural Precursor Cell Growth and Differentiation

Neurospheres (NSs) are clonal cellular aggregates composed of neural stem cells and progenitors. A comprehensive description of their proliferation and differentiation regulation is an essential prerequisite for their use in biotherapies. Cytokines are essential molecules regulating cell precursor fate. Using a gene-array strategy, we conducted a descriptive and functional analysis of endogenous cytokines and receptors expressed by spinal cord-derived NSs during their growth or their differentiation into neuronal and glial cells. NSs were found to express approximately 100 receptor subunits and cytokine/secreted developmental factors. Several angiogenic factors and receptors that could mediate neural precursor cell-endothelial cell relationships were detected. Among them, receptor B for endothelins was highly expressed, and endothelins were found to increase NS growth. In contrast, NSs express receptors for ciliary neurotrophic factor (CNTF), bone morphogenetic protein (BMP), interferon (IFN)-gamma, or tumor necrosis factor (TNF)-alpha, which, when added in the growth phase, led to a dramatic growth reduction followed by a reduction or a loss of oligodendrocyte formation on differentiation. In addition, NSs synthesize fibroblast growth factor 2/epidermal growth factor (FGF2/EGF)-regulated endogenous cytokines that participate in their growth and differentiation. Notably, BMP-7 and CNTF were expressed during expansion, but upon differentiation there was a remarkable switch from BMP-7 to BMP-4 and -6 and a sharp increase of CNTF. Reintroduction of growth factors reverses the BMP expression profile, indicating growth factor-BMP cross-regulations. The role of endogenous CNTF was investigated by deriving NSs from CNTF knockout mice. These NSs have an increased growth rate associated with reduction of apoptosis and generate astrocytes with a reduced glial fibulary acidic protein (GFAP) content. These results demonstrate the combined role of endogenous and exogenous cytokines in neural precursor cell growth and differentiation.

High-level activation of cyclic AMP signaling attenuates bone morphogenetic protein 2-induced sympathoadrenal lineage development and promotes melanogenesis in neural crest cultures

The intensity of cyclic AMP (cAMP) signaling is a differential instructive signal in neural crest (NC) cell specification. By an unknown mechanism, sympathoadrenal lineage specification is suppressed by high-level activation of cAMP signaling. In NC cultures, high-level activation of cAMP signaling mediates protein kinase A (PKA)-dependent Rap1-B-Raf-ERK1/2 activation, leading to cytoplasmic accumulation of phospho-Smad1, thus terminating bone morphogenetic protein 2 (BMP2)-induced sympathoadrenal cell development. Concurrently, cAMP signaling induces transcription of the melanocyte-determining transcription factor Mitf and melanogenesis. dnACREB and E1A inhibit Mitf expression and melanogenesis, supporting the notion that CREB activation is necessary for melanogenesis. However, constitutively active CREB(DIEDML) without PKA activation is insufficient for Mitf expression and melanogenesis, indicating PKA regulates additional aspects of Mitf transcription. Thus, high-level activation of cAMP signaling plays a dual role in NC cell differentiation: attenuation of BMP2-induced sympathoadrenal cell development and induction of melanogenesis. We conclude the intensity of activation of signal transduction cascades determines cell lineage segregation mechanisms.

WNT1 and WNT3a promote expansion of melanocytes through distinct modes of action

Summary WNT1 and WNT3a have been described as having redundant roles in promoting the development of neural crest-derived melanocytes (NC-Ms). We used cell lineage restricted retroviral infections to examine the effects of WNT signaling on defined cell types in neural crest cultures. RCAS retroviral infections were targeted to melanoblasts (NC-M precursor cells) derived from transgenic mice that express the virus receptor, TVA, under the control of a melanoblast promoter (DCT). As expected, over 90% of DCT-TVA+ cells expressed early melanoblast markers MITF and KIT. However, by following the fate of infected cells in standard culture conditions, we find that only 5% of descendents were NC-Ms. The majority of the descendents were not NC-Ms, but expressed smooth muscle cell markers, demonstrating that mammalian melanoblasts are not committed to the NC-M lineage. RCAS infection of DCT-TVA+ cells demonstrated that overexpression of canonical WNT signaling genes (betaCAT, WNT3a or WNT1) can increase NC-M numbers in an endothelin dependent manner. However, WNT1 and WNT3a have different modes of action with respect to melanoblast fate. Intrinsic over-expression of betaCAT or WNT3a can increase NC-M numbers by biasing the fate of DCT-TVA+ cells to NC-Ms. In contrast, the DCT-TVA+ melanoblasts cannot respond to WNT1 signaling and do not alter their fate towards NC-M. Instead, WNT1 only increases NC-M numbers through paracrine signaling on melanoblast precursors to increase the numbers of neural crest cells that become NC-Ms.

Enteric nervous system progenitors are coordinately controlled by the G protein-coupled receptor EDNRB and the receptor tyrosine kinase RET

The enteric nervous system (ENS) in vertebrates is derived mainly from vagal neural crest cells that enter the foregut and colonize the entire wall of the gastrointestinal tract. Failure to completely colonize the gut results in the absence of enteric ganglia (Hirschsprung's disease). Two signaling systems mediated by RET and EDNRB have been identified as critical players in enteric neurogenesis. We demonstrate that interaction between these signaling pathways controls ENS development throughout the intestine. Activation of EDNRB specifically enhances the effect of RET signaling on the proliferation of uncommitted ENS progenitors. In addition, we reveal novel antagonistic roles of these pathways on the migration of ENS progenitors. Protein kinase A is a key component of the molecular mechanisms that integrate signaling by the two receptors. Our data provide strong evidence that the coordinate and balanced interaction between receptor tyrosine kinases and G protein-coupled receptors controls the development of the nervous system in mammals.

Blood vessels and nerves: common signals, pathways and diseases

Both blood vessels and nerves are vital channels to and from tissues. Recent genetic insights show that they have much more in common than was originally anticipated. They use similar signals and principles to differentiate, grow and navigate towards their targets. Moreover, the vascular and nervous systems cross-talk and, when dysregulated, this contributes to medically important diseases. The realization that both systems use common genetic pathways should not only form links between vascular biology and neuroscience, but also promises to accelerate the discovery of new mechanistic insights and therapeutic opportunities.