![]() Each sustentacular cell extends a process terminating in an end foot at the basal lamina. Sustentacular cells completely surround the cell body and dendrite of each mature OSN. At the apical surface of the olfactory epithelium are the cell bodies of the sustentacular cells (gold). ![]() Immature OSNs differentiate into mature OSNs (dark blue), the most abundant cell type in this tissue. Nascent OSNs rapidly transition into immature OSNs (medium blue), whose cell bodies are apical to the nascent OSNs. Immediate neuronal precursor GBCs differentiate into nascent OSNs (light blue) whose cell bodies lie apical to the GBCs. At least 3 subtypes of GBCs exist in the OSN lineage: a multipotent GBC (light green), which gives rise to a transit-amplifying GBC expressing the neural fate transcription factor Ascl1 (lightest blue), and then an immediate neuronal precursor GBC expressing the transcription factor Neurog1 (light blue). Immature sustentacular cells (yellow) are depicted as residing (transiently) in the GBC cell layer. HBCs are multipotent progenitor cells capable of giving rise to globose basal cells (GBCs) that sit apical to the HBCs and are capable of differentiating directly into sustentacular cells (gold). Horizontal basal cells (HBCs, dark green) lie flat on the basal lamina. The olfactory epithelium is separated from the underlying lamina propria by a basal lamina. The cell types of the olfactory epithelium. For permissions, please e-mail: Disclaimer ![]() Immature OSNs also have a primary cilium, but its role is unknown, unlike the critical role in proliferation and differentiation played by the primary cilium of the olfactory epithelium's horizontal basal cell.ĭifferentiation neural development olfactory receptor smell transcriptional regulation. The cilia from adjoining OSNs form a meshwork in the olfactory mucus and are the site of olfactory transduction. Many of these genes encode proteins necessary for mature function of axons and synapses or for completing the elaboration of non-motile cilia, which began extending from the newly formed dendritic knobs of immature OSNs. The transition to maturity depends on massive expression of one allele of one odorant receptor gene, and this results in expression of the last 8% of genes expressed by mature OSNs. Late-stage immature OSNs begin expressing genes encoding proteins important for energy production and neuronal homeostasis that carry over into mature OSNs. Early-stage immature OSNs initiate expression of genes encoding key transcriptional regulators and structural proteins necessary for further neuritogenesis. Immature OSN differentiation requires about a week and at least 2 stages. Nascent OSNs become immature OSNs within 24-48 h. Basal progenitor cells of the olfactory epithelium transition into nascent OSNs marked by Cxcr4 expression and the initial extension of basal and apical neurites. The extensive changes in gene expression accompanying OSN differentiation in mice are largely known, especially the transcriptional regulators responsible for altering gene expression, revealing much about how differentiation proceeds. Olfactory sensory neurons (OSNs) are bipolar neurons, unusual because they turn over continuously and have a multiciliated dendrite.
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