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Epidermal ectoderm

Epidermal ectoderm gives rise to teeth, hair, nails, mammary glands, scales and feathers. Via epithelio-mesenchymal interaction, underlying mesenchyme determines which structures are formed from the epidermis. For example, if chicken thigh mesoderm is grafted beneath wing ectoderm, then the wing ectoderm will form thigh feathers rather than wing feathers. Epithelio-mesenchymal interaction occurs in three steps:

ProcessOverview
InitiationSignals provide positional information so that organs form in the correct place. For example, secreted signals control initiation of tooth development so that the right number of teeth develop and with proper spacing.
MorphogenesisEpithelial and mesenchymal cells interact to form a rudiment, for example a tooth bud or hair follicle.
DifferentiationCells differentiate to form specific structures. For example: tooth bud epithelial cells differentiate into enamel-producing cells; and hair follicle epithelial cells differentiate into hair-producing cells.
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