Mia Patel
The neural crest is a critical structure in the development of vertebrates, including birds such as chickens. In chicken embryos, the neural crest forms at the dorsal region of the neural tube, specifically at the junction between the neural and non-neural ectoderm. This region is sometimes referred to as the fourth germ layer due to its significance. The neural crest cells migrate extensively throughout the embryo, giving rise to various structures, including the head, peripheral nervous system, sensory and sympathetic ganglia, heart regions, adrenal cells, head bones, teeth, and muscle cells. The study of neural crest migration and development in chicken embryos has been instrumental in advancing our understanding of developmental biology, providing insights into the formation and differentiation of these crucial cells.
| Characteristics | Values |
|---|---|
| Where the neural crest forms | Neural crest cells originate from the dorsalmost region of the neural tube |
| Neural crest cells emerge from the neural tube early in development | |
| Neural crest cells arise from the dorsal neural tube | |
| The neural crest arises at two junctions, one on each side of the midline of the neural plate, between neural and non-neural ectoderm | |
| The neural crest is first distinguishable during the neurula stage | |
| The neural crest is derived from the ectoderm | |
| The neural crest is sometimes called the fourth germ layer |
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What You'll Learn
- Neural crest cells emerge from the neural tube
- Neural crest cells migrate extensively throughout the embryo
- Neural crest cells form most of the head and peripheral nervous system
- Neural crest cells produce multiple cell types
- Neural crest cells lose their epithelial nature and transform into migratory cells
Neural crest cells emerge from the neural tube
The neural crest arises at two junctions, one on each side of the midline of the neural plate, between neural and non-neural ectoderm. As neurulation progresses and the neural tube forms, the two junctions meet at the top of the neural tube. The neural crest then separates from the neural tube through a process called delamination and migrates away from it.
Neural crest cells originate from the neural folds through interactions of the neural plate with the presumptive epidermis. In cultures of embryonic chick ectoderm, the presumptive epidermis can induce neural crest formation in the connected neural plate. These changes can be replicated by culturing neural plate cells with bone morphogenetic proteins 4 and 7 (BMP4 and BMP7), which are secreted by the presumptive epidermis. BMP4 and BMP7 induce the expression of the Slug protein and the RhoB protein in the cells destined to become neural crest cells. If either of these proteins is inactivated or inhibited from forming, the neural crest cells will not emigrate from the neural tube.
Neural crest cells are initially part of the dorsal neural tube, with a clear epithelial character. Later, they transform into actively motile mesenchymal cells. These cells migrate extensively throughout the embryo and form most of the head and peripheral nervous system, giving rise to sensory and sympathetic ganglia, heart regions, adrenal cells, head bones, teeth, muscle cells, sensory organs, melanocytes, and other cell types.
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Neural crest cells migrate extensively throughout the embryo
Neural crest cells emerge from the dorsal neural tube during the early development of the embryo. They migrate extensively throughout the embryo, forming most of the head and peripheral nervous system. The neural crest cells that migrate along the dorsolateral pathway become melanocytes, the melanin-forming pigment cells. They travel through the dermis, entering the ectoderm through minute holes in the basal lamina.
Neural crest migration can be divided into three stages: emigration from the neural tube, migration along defined pathways, and cessation of migration. During the first stage, neural crest cells lose their epithelial nature within the neural tube and transform into migratory, mesenchymal cell types. Once the basal lamina becomes permeable, neural crest cells can begin migrating throughout the embryo.
The neural crest cells then migrate into the periphery along stereotypical paths to a number of sites at which they stop and differentiate into a wide variety of derivatives. These include sensory neurons, autonomic neurons, glia, melanocytes, cells of the adrenal medulla, and, additionally in the head, bone, cartilage, connective tissue, and smooth muscle cells.
In the head of the embryo, neural crest cells pour out from the developing brain into a periphery that is devoid of somites. Here, the early migratory cells move ventrolaterally and populate the pharyngeal arches and facial prominences, generating ectomesenchymal derivatives: bone, cartilage, and connective tissue. The late-migrating neural crest cells stay closer to the neural tube and generate neurons and glia of the cranial ganglia.
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Neural crest cells form most of the head and peripheral nervous system
Neural crest cells emerge from the neural tube early in the development of a chicken embryo. They migrate extensively throughout the embryo and form most of the head and peripheral nervous system. The neural crest is interesting because of its unique origin, development, and differentiation. These cells are initially part of the dorsal neural tube, with a clear epithelial character. Later, they transform into actively motile mesenchymal cells.
The neural crest first appears in the embryo during gastrulation, the invagination and spreading process by which a blastula becomes a gastrula. However, it becomes distinguishable during the neurula stage, when the neural plate folds and transforms into the neural tube, the structure that will eventually develop into the central nervous system. The neural crest arises at two junctions, one on each side of the midline of the neural plate, between neural and non-neural ectoderm. As neurulation progresses and the neural tube forms, the two junctions meet at the top of the neural tube. Then the neural crest separates from the neural tube, a process called delamination, and subsequently migrates away from the neural tube.
Neural crest cells give rise to sensory and sympathetic ganglia, heart regions, adrenal cells, head bones, teeth, muscle cells, sensory organs, and melanocytes, among other cell types. The neural crest is sometimes referred to as the fourth germ layer because of its importance. It has been argued that the presence of the neural crest was the basis for vertebrate-specific features, such as sensory ganglia and the cranial skeleton.
The development of the neural crest is underpinned by a gene regulatory network, which confers cell characteristics such as multipotency and migratory capabilities. Understanding the molecular mechanisms of neural crest formation is important for our knowledge of human disease because of its contributions to multiple cell lineages. Abnormalities in neural crest development can cause neurocristopathies, including conditions such as frontonasal dysplasia and DiGeorge syndrome.
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Neural crest cells produce multiple cell types
Neural crest cells are highly versatile and can differentiate into several different cell types. They are formed during the gastrulation stage of embryo development, specifically during neurulation, when the neural plate folds and transforms into the neural tube. The neural crest arises at two junctions between the neural and non-neural ectoderm on each side of the midline of the neural plate. As neurulation progresses, these junctions meet at the top of the neural tube, and the neural crest separates and migrates away.
Neural crest cells emerge from the neural tube and migrate extensively throughout the embryo. These cells are initially epithelial but undergo an epithelial-to-mesenchymal transition to become migratory mesenchymal cells. This transformation is crucial for their ability to differentiate into various cell types.
The neural crest cells give rise to a diverse range of cell lineages, including melanocytes, craniofacial cartilage and bone, smooth muscle, dentin, peripheral and enteric neurons, adrenal medulla, and glia. They are responsible for forming most of the head and peripheral nervous system, generating sensory and sympathetic ganglia, heart regions, adrenal cells, head bones, teeth, muscle cells, sensory organs, and more.
The neural crest can be divided into different types based on their location and function. For example, the cranial (cephalic) neural crest cells migrate dorsolaterally to produce the craniofacial mesenchyme, differentiating into cartilage, bone, cranial neurons, glia, and connective tissues of the face. They also contribute to the development of the thyroid glands and the formation of teeth and bones in the middle ear and jaw.
The trunk neural crest cells take one of two migratory pathways. Some become pigment-synthesizing melanocytes, migrating dorsolaterally into the ectoderm. Others take a ventrolateral pathway through the anterior half of each sclerotome, contributing to the formation of the vertebral cartilage of the spine.
The vagal (neck) neural crest cells produce parasympathetic neurons that use acetylcholine as their neurotransmitter, while the thoracic (chest) neural crest cells produce sympathetic neurons that use norepinephrine, demonstrating the ability of neural crest cells to differentiate into multiple cell types depending on their location within the embryo.
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Neural crest cells lose their epithelial nature and transform into migratory cells
Neural crest cells emerge from the neural tube during early development. They are initially part of the dorsal neural tube, with a clear epithelial character. However, to migrate extensively throughout the embryo, they need to transform into actively motile mesenchymal cells. This transformation involves a process called delamination, which involves the separation of tissue into different populations, specifically neural crest cells separating from the surrounding tissue. This delamination is controlled by Bmps, most prominently Bmp-4, which is expressed at the dorsal midline of the neural tube.
The delamination process involves a full or partial epithelial-mesenchymal transition (EMT). EMT is a series of events coordinating a change from an epithelial to a mesenchymal phenotype. This transition entails radical alterations in the relationship between the neural crest cells and their neighbours within the dorsal neural tube. Specifically, the delamination of neural crest cells requires a switch in the repertoire of cell adhesion molecules expressed by these cells. The crest cells down-regulate N-CAM and N-cadherin, which are generally expressed by cells of the neural tube. They also lose the expression of cadherin-6b, which is expressed within the neural tube by the cells of the dorsalmost region. The crest cells then upregulate cadherin-7.
Before delamination, presumptive neural crest cells are anchored to neighbouring cells by tight junction proteins such as occludin and cell adhesion molecules such as NCAM and N-Cadherin. Dorsally expressed BMPs initiate delamination by inducing the expression of the zinc finger protein transcription factors snail, slug, and twist. These factors play a direct role in inducing the epithelial-mesenchymal transition by reducing the expression of occludin and N-Cadherin, promoting the modification of NCAMs with polysialic acid residues to decrease adhesiveness, and promoting the expression of proteases capable of degrading cadherins.
The migration of neural crest cells appears to be regulated by the extracellular matrix and by soluble factors secreted by potential destinations. For example, if stem cell factor is secreted from cells that do not usually synthesize this protein (such as the cheek epithelium or footpads), neural crest cells will enter those regions and become melanocytes. Neural crest cells also begin expressing integrins that associate with extracellular matrix proteins, including collagen, fibronectin, and laminin, during migration.
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