Air Quality and Health Impact of Future Fossil Fuel Use for Electricity Generation and Transport in Africa.

Africa has ambitious plans to address energy deficits and sustain economic growth with fossil fueled power plants. The continent is also experiencing faster population growth than anywhere else in the world that will lead to proliferation of vehicles. Here, we estimate air pollutant emissions in Africa from future (2030) electricity generation and transport.

The diverse neural crest: from embryology to human pathology.

We review here some of the historical highlights in exploratory studies of the vertebrate embryonic structure known as the neural crest. The study of the molecular properties of the cells that it produces, their migratory capacities and plasticity, and the still-growing list of tissues that depend on their presence for form and function, continue to enrich our understanding of congenital malformations, paediatric cancers and evolutionary biology. Developmental biology has been key to our understanding of the neural crest, starting with the early days of experimental embryology and through to today, when increasingly powerful technologies contribute to further insight into this fascinating vertebrate cell population.

The dependence receptor TrkC regulates the number of sensory neurons during DRG development.

The development of the sensory nervous system is the result of fine-tuned waves of neurogenesis and apoptosis which control the appropriate number of precursors and newly generated neurons and orient them toward a specific lineage. Neurotrophins and their tyrosine-kinase receptors (RTK) orchestrate this process. They have long been in the scope of the neurotrophic theory which established that a neuron is committed to die unless a trophic factor generated by its target provides it with a survival signal.

The "beginnings" of the neural crest.

The neural crest has been the main object of my investigations during my career in science, up to now. It is a fascinating topic for an embryologist because of its two unique characteristics: its large degree of multipotency and the fact that its development involves a phase during which its component cells migrate all over the embryo and settle in elected sites where they differentiate into a large variety of cell types. Thus, neural crest development raises several specific questions that are at the same time, of general interest: what are the mechanisms controlling the migratory behavior of the cells that detach from the neural plate borders? What are the migration routes taken by the neural crest cells and the environmental factors that make these cells stop in elected sites where they differentiate into a definite series of cell types? When I started to be interested in the neural crest, in the late 1960s, this embryonic structure was the subject of investigations of only a small number of developmental biologists.

The issue of the multipotency of the neural crest cells.

In the neural primordium of vertebrate embryos, the neural crest (NC) displays a unique character: the capacity of its component cells to leave the neural primordium, migrate along definite (and, for long, not identified) routes in the developing embryo and invade virtually all tissues and organs, while producing a large array of differentiated cell types. The most striking diversity of the NC derivatives is found in its cephalic domain that produces, not only melanocytes and peripheral nerves and ganglia, but also various mesenchymal derivatives (connective tissues, bones, cartilages…) which, in other parts of the body, are mesoderm-derived. The aim of this article was to review the large amount of work that has been devoted to solving the problem of the differentiation capacities of individual NC cells (NCC) arising from both the cephalic and trunk levels of the neural axis.

Easy xeno-free and feeder-free method for isolating and growing limbal stromal and epithelial stem cells of the human cornea.

Epithelial and stromal stem cells are required to maintain corneal transparency. The aim of the study was to develop a new method to isolate and grow both corneal stromal (SSC) and epithelial limbal (LSC) stem cells from small human limbal biopsies under culture conditions in accordance with safety requirements mandatory for clinical use in humans. Superficial limbal explants were retrieved from human donor corneo-scleral rims.

Respective contribution of the cephalic neural crest and mesoderm to SIX1-expressing head territories in the avian embryo.

Background: Vertebrate head development depends on a series of interactions between many cell populations of distinct embryological origins. Cranial mesenchymal tissues have a dual embryonic source: - the neural crest (NC), which generates most of craniofacial skeleton, dermis, pericytes, fat cells, and tenocytes; and - the mesoderm, which yields muscles, blood vessel endothelia and some posterior cranial bones. The molecular players that orchestrate co-development of cephalic NC and mesodermal cells to properly construct the head of vertebrates remain poorly understood.

The Pluripotency of Neural Crest Cells and Their Role in Brain Development.

The neural crest (NC) is, in the Chordate phylum, an innovation of vertebrates, which exhibits several original characteristics: its component cells are pluripotent and give rise to both ectodermal and mesodermal cell types. Moreover, during the early stages of neurogenesis, the NC cells exert a paracrine stimulating effect on the development of the preotic brain.

The neural crest, a multifaceted structure of the vertebrates.

In this review, several features of the cells originating from the lateral borders of the primitive neural anlagen, the neural crest (NC) are considered. Among them, their multipotentiality, which together with their migratory properties, leads them to colonize the developing body and to participate in the development of many tissues and organs. The in vitro analysis of the developmental capacities of single NC cells (NCC) showed that they present several analogies with the hematopoietic cells whose differentiation involves the activity of stem cells endowed with different arrays of developmental potentialities.

Multiplex cell and lineage tracking with combinatorial labels.

We present a method to label and trace the lineage of multiple neural progenitors simultaneously in vertebrate animals via multiaddressable genome-integrative color (MAGIC) markers. We achieve permanent expression of combinatorial labels from new Brainbow transgenes introduced in embryonic neural progenitors with electroporation of transposon vectors. In the mouse forebrain and chicken spinal cord, this approach allows us to track neural progenitor's descent during pre- and postnatal neurogenesis or perinatal gliogenesis in long-term experiments.

Environmental factors unveil dormant developmental capacities in multipotent progenitors of the trunk neural crest.

The neural crest (NC), an ectoderm-derived structure of the vertebrate embryo, gives rise to the melanocytes, most of the peripheral nervous system and the craniofacial mesenchymal tissues (i.e., connective, bone, cartilage and fat cells).

The dependence receptor TrkC triggers mitochondria-dependent apoptosis upon Cobra-1 recruitment.

The neurotrophin receptor TrkC was recently identified as a dependence receptor, and, as such, it triggers apoptosis in the absence of its ligand, NT-3. The molecular mechanism for apoptotic engagement involves the double cleavage of the receptor's intracellular domain, leading to the formation of a proapoptotic "killer" fragment (TrkC KF). Here, we show that TrkC KF interacts with Cobra1, a putative cofactor of BRCA1, and that Cobra1 is required for TrkC-induced apoptosis.

Isolation and differentiation properties of neural crest stem cells.

A wide array of neural and non-neural cell types arises from the neural crest during vertebrate embryogenesis. The neural crest forms transiently in the dorsal neural primordium to yield migratory cells that will invade nearly all tissues and later, differentiate into bones and cartilages, vascular smooth muscle cells, connective tissues, neurons and glial cells of the peripheral nervous system, endocrine cells, and melanocytes. Due to the amazingly diversified array of cell types they generate, the neural crest cells represent an attractive model in the stem cell field.

The neural crest in vertebrate evolution.

Vertebrates belong to the group of chordates characterized by a dorsal neural tube and an anteroposterior axis, the notochord. They are the only chordates to possess an embryonic and pluripotent structure associated with their neural primordium, the neural crest (NC). The NC is at the origin of multiple cell types and plays a major role in the construction of the head, which has been an important asset in the evolutionary success of vertebrates.

Neural crest progenitors and stem cells: from early development to adulthood.

In the vertebrate embryo, the neural crest forms transiently in the dorsal neural primordium to yield migratory cells that will invade nearly all tissues and later, will differentiate into bones and cartilages, neurons and glia, endocrine cells, vascular smooth muscle cells and melanocytes. Due to the amazingly diversified array of cell types it produces, the neural crest is an attractive model system in the stem cell field. We present here in vivo and in vitro studies of single cell fate, which led to the discovery and the characterization of stem cells in the neural crest of avian and mammalian embryos.

Modulation of Bmp4 signalling in the epithelial-mesenchymal interactions that take place in early thymus and parathyroid development in avian embryos.

Epithelial-mesenchymal interactions are crucial for the development of the endoderm of the pharyngeal pouches into the epithelia of thymus and parathyroid glands. Here we investigated the dynamics of epithelial-mesenchymal interactions that take place at the earliest stages of thymic and parathyroid organogenesis using the quail-chick model together with a co-culture system capable of reproducing these early events in vitro. The presumptive territories of thymus and parathyroid epithelia were identified in three-dimensionally preserved pharyngeal endoderm of embryonic day 4.

[Phenotypic plasticity of neural crest-derived melanocytes and Schwann cells].

Melanocytes, the pigmented cells of the skin, and the glial Schwann cells lining peripheral nerves are developmentally derived from an early and transient ectodermal structure of the vertebrate embryo, the neural crest, which is also at the origin of multiple neural and non-neural cell types. Besides melanocytes and neural cells of the peripheral nervous system, the neural crest cells give rise to mesenchymal cell types in the head, which form most of the craniofacial skeleton, dermis, fat tissue and vascular musculo-connective components. How such a wide diversity of differentiation fates is established during embryogenesis and is later maintained in adult tissues are among key questions in developmental and stem cell biology.

The cephalic neural crest of amniote vertebrates is composed of a large majority of precursors endowed with neural, melanocytic, chondrogenic and osteogenic potentialities.

In the amniote embryo, the neural crest (NC) has the unique capacity to give rise to neuronal and glial cells in the peripheral nervous system (PNS), melanocytes and mesenchymal cells including those forming the head skeleton and connective tissues. In the trunk, mesenchymal cells are derived from the mesoderm. The question was raised whether the NC-derived head mesenchyme arises from a lineage separate from the neural-melanocytic one, or if both skeletogenic and neural-melanocytic derivatives originate from a common putative stem cell in the early cephalic NC.

High frequency of cephalic neural crest cells shows coexistence of neurogenic, melanogenic, and osteogenic differentiation capacities.

The neural crest (NC) is a vertebrate innovation that distinguishes vertebrates from other chordates and was critical for the development and evolution of a "New Head and Brain." In early vertebrates, the NC was the source of dermal armor of fossil jawless fish. In extant vertebrates, including mammals, the NC forms the peripheral nervous system, melanocytes, and the cartilage and bone of the face.

The stem cells of the neural crest.

In the vertebrate embryo, the neurectodermal neural crest cells (NCC) have remarkably broad potencies, giving rise, after a migratory phase, to neurons and glial cells in the peripheral nervous system, and to skin melanocytes, being all designated here as "neural" derivatives. NC-derived cells also include non-neural, "mesenchymal" cell types like chondrocytes and bone cells, myofibroblasts and adipocytes, which largely contribute to the head structures in amniotes. Similar to the blood cell system, the NC is therefore a valuable model to investigate the mechanisms of cell lineage diversification in vertebrates.

Sonic Hedgehog promotes the development of multipotent neural crest progenitors endowed with both mesenchymal and neural potentials.

In the vertebrate embryo, the cephalic neural crest cells (CNCCs) produce cells belonging to two main lineages: the neural [including neurons, glial cells of the peripheral nervous system (PNS), and melanocytes] and the mesenchymal (chondrocytes, osteoblasts, smooth muscle cells, and connective tissue cells), whereas the trunk NCCs (TNCCs) in amniotes yield only neural derivatives. Although multipotent cells have previously been evidenced by in vitro clonal analysis, the issue as to whether all of the mesenchymal and neural phenotypes can be derived from a unique NC stem cell has remained elusive. In the present work, we devised culture conditions that led us to identify a highly multipotent NCC endowed with both neural and mesenchymal potentials, which lies upstream of all the other NC progenitors known so far.

Neural crest progenitors and stem cells.

In the vertebrate embryo, multiple cell types originate from a common structure, the neural crest (NC), which forms at the dorsal tips of the neural epithelium. The NC gives rise to migratory cells that colonise a wide range of embryonic tissues and later differentiate into neurones and glial cells of the peripheral nervous system (PNS), pigment cells (melanocytes) in the skin and endocrine cells in the adrenal and thyroid glands. In the head and the neck, the NC also yields mesenchymal cells that form craniofacial cartilages, bones, dermis, adipose tissue, and vascular smooth muscle cells.

The generation of adipocytes by the neural crest.

Fat cells (adipocytes) develop from adipocyte precursor cells (preadipocytes) that themselves derive from mesenchymal progenitors. Although the events controlling preadipocyte differentiation into mature adipocytes have been largely explored, the mechanisms that direct mesenchymal progenitors down the adipocyte pathway remain unknown. Similarly, although adipocytes are generally thought to derive from mesoderm, key information is lacking regarding the origin and the development of the adipose tissue during embryogenesis.

The contribution of the neural crest to the vertebrate body.

As a transitory structure providing adult tissues of the vertebrates with very diverse cell types, the neural crest (NC) has attracted for long the interest of developmental biologists and is still the subject of ongoing research in a variety of animal models. Here we review a number of data from in vivo cell tracing and in vitro single cell culture experiments, which gained new insights on the mechanisms of cell migration, proliferation and differentiation during NC ontogeny. We put emphasis on the role of Hox genes, morphogens and interactions with neighbouring tissues in specifying and patterning the skeletogenic NC cells in the head.