Cardiac neural crest cells

Neural crest cells are a group of temporary, multipotent (can give rise to some other types of cells but not all) cells that are pinched off during the formation of the neural tube (precursor to the spinal cord and brain) and therefore are found at the dorsal (top) region of the neural tube during development. They are derived from the ectoderm germ layer, but are sometimes called the fourth germ layer because they are so important and give rise to so many other types of cells. They migrate throughout the body and create a large number of differentiated cells such as neurons, glial cells, pigment-containing cells in skin, skeletal tissue cells in the head, and many more. Neural crest cells are a group of temporary, multipotent (can give rise to some other types of cells but not all) cells that are pinched off during the formation of the neural tube (precursor to the spinal cord and brain) and therefore are found at the dorsal (top) region of the neural tube during development. They are derived from the ectoderm germ layer, but are sometimes called the fourth germ layer because they are so important and give rise to so many other types of cells. They migrate throughout the body and create a large number of differentiated cells such as neurons, glial cells, pigment-containing cells in skin, skeletal tissue cells in the head, and many more. Cardiac neural crest cells (CNCCs) are a type of neural crest cells that migrate to the circumpharyngeal ridge (an arc-shape ridge above the pharyngeal arches) and then into the 3rd, 4th and 6th pharyngeal arches and the cardiac outflow tract (OFT). They extend from the otic placodes (the structure in developing embryos that will later form the ears) to the third somites (clusters of mesoderm that will become skeletal muscle, vertebrae and dermis). The cardiac neural crest cells have a number of functions including creation of the muscle and connective tissue walls of large arteries; parts of the cardiac septum; parts of the thyroid, parathyroid and thymus glands. They differentiate into melanocytes and neurons and the cartilage and connective tissue of the pharyngeal arches. They may also contribute to the creation of the carotid body, the organ which monitors oxygen in the blood and regulates breathing. Induction is the differentiation of progenitor cells into their final designation or type. The progenitor cells which will become CNCCs are found in the epiblast about Henson's node. Progenitor cells are brought into the neural folds. Molecules such as Wnt, fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) provide signals which induce the progenitor cells to become CNCCs. Little is known about the signal cascade that promotes neural crest induction. However, it is known that an intermediate level of BMP is required: if BMP is too high or too low, the cells do not migrate. After induction, CNCCs lose their cell to cell contacts. This allows them to move through the extracellular matrix and interact with its components. The CNCCs, with the assistance of their filopodia and lamellipodia (actin containing extensions of cytoplasm that allow a cell to probe its path of migration), leave the neural tube and migrate along a dorsolateral pathway to the circumpharyngeal ridge. Along this pathway, CNCCs link together to form a stream of migrating cells. Cells at the front of the migration stream have a special polygonal shape and proliferate at a faster rate than trailing cells. At the circumpharyngeal arch the CNCCs must pause in their migration while the pharyngeal arches form. The CNCCs continue their migration into the newly formed pharyngeal arches, particularly the third, fourth and sixth arches. In the pharyngeal arches the CNCCs assist in the formation of the thyroid and parathyroid glands. The leading cells have long filopodia that assist migration while cells in the middle of the migration have protrusions at their front and back allowing them to interact and communicate with leading cells, trailing cells and receive signals from the extracellular matrix.