page_title: Olfactory epithelium
section_title: Olfactory placode
hierarchical_section_title: Olfactory epithelium / Development / Olfactory placode
caption_attribution_description: English: Embryonic morphogen signaling on olfactory placode and neural crest cells contributes to formation of neurogenic and non-neurogenic tissue of the olfactory epithelium.
context_page_description: The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures
  9 cm² and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils. The olfactory epithelium is the part of the olfactory system directly responsible for detecting odors.
context_section_description: Placodes are transient, focal aggregations of ectoderm located in the developmental region of the future vertebrate head, and give rise to sensory organs. Early cranial sensory placodes are marked by expression of Six1, part of the Six family of transcription factors that regulate preplacodal ectoderm specification. The olfactory placode forms as two thickenings of non-neural region of embryonic ectoderm. In mice, the olfactory placode derives from an anterior portion of the neural tube, ~9-9.5 days into development and not long after the closure of the neural plate. Development of the olfactory placode requires the presence underlying neural crest-derived mesenchymal tissue. The specification of the olfactory placode tissue involves signaling of multiple gene networks, beginning with signals from bone morphogenetic proteins (BMP), retinoic acid (RA), and fibroblast growth factor (FGF), specifically FGF8. The resulting regulated downstream expression of transcription factors, such as Pax6, Dlx3, Sox2, and others, within the presumptive olfactory placode are crucial for sub-regionalization within the future olfactory epithelium and is responsible for the diversity of cells that compose the future epithelium.
  Similar to the other embryonic placodes, the olfactory placode gives rise to both neural and non-neural structures, ultimately resulting in the formation of the nasal epithelium. The specification of neural versus non-neural tissue involves signals both within the olfactory placode, and between the olfactory placode and the underlying mesenchymal compartment. Continued signaling by BMP, FGF, and RA, the morphogens that initially induced placode formation, collectively coordinate the patterning of olfactory placode tissue into the future distinct cell types that make up the olfactory epithelium. The cell types derived from the olfactory placode include:
  Neural: olfactory sensory neurons, LHRH-secreting neurons, and ganglion cells
  Non-neuronal: basal cells, olfactory supporting cells, ciliated cells, Bowman’s glands, Schwann cells, submucosal glands, and brush cells
  However, there is significant evidence for an additional neural crest-origin for many of these cell types as well.
caption: Embryonic morphogen signaling on olfactory placode and neural crest cells contributes to formation of neurogenic and non-neurogenic tissue of the olfactory epithelium.
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