Corm orn gord11/9/2022 ![]() ![]() Retroviral lineage studies proposed that ORNs derive from GBCs but not from HBCs, which led to a long-prevailing model holding that the stem cells giving rise to ORNs reside in the GBC population and that HBCs are outside the ORN lineage. On the other hand, HBCs divide infrequently and express keratin 5 (K5) and keratin 14 (K14) but are negative for neuronal markers. GBCs are associated with active proliferation and contain direct ORN precursor cells positive for early neuronal differentiation markers, such as Mash1 and Neurogenin1. HBCs are situated most basally in the OE and are directly attached to the basal lamina, whereas GBCs lie immediately above the HBC layer. The progenitors of the ORN lineage reside in the basal compartment of the OE, which consists of two distinct cell types: globose basal cells (GBCs) and horizontal basal cells (HBCs). Sustentacular cells are neuron-supporting cells and occupy the most apical layer of the OE, whereas Bowman’s glands secrete mucus to the outer surface of the epithelium via ducts that extend through the OE. On the other hand, two types of non-neuronal cells are present in the OE: sustentacular cells and cells of the Bowman’s glands and ducts. The dendrites of mature ORNs are exposed to the apical surface of the OE, whereas their axons extend basally and exit the OE, eventually projecting to the olfactory bulb. It consists mainly of ORNs, which migrate to the apical region of the OE as they mature. The OE is a pseudostratified neuroepithelium, structurally and functionally highly conserved among mammals. This robust regenerative capacity, together with the fact that the OE is a simple neuroepithelium containing only one type of neuron, namely the ORN, offers an ideal system for the study of neural stem cells in the adult. The adult olfactory epithelium (OE) is capable of rapid neuronal regeneration and functional recovery after extensive damage to the tissue, and even under normal physiological conditions, steady-state neurogenesis takes place to continuously replace apoptotic olfactory receptor neurons (ORNs). The mammalian olfactory neuroepithelium has long been known for its unique characteristic of actively generating neurons throughout adulthood, at a rate that by far exceeds neurogenesis in the subventricular zone and dentate gyrus. Our findings demonstrate a crucial role for HBCs as multipotent progenitors in the adult OE, acting during normal neuronal turnover as well as in acute regeneration upon injury. Moreover, upon selective depletion of mature ORNs by olfactory bulbectomy, HBCs give rise to more neurons. ![]() This occurs in a temporally controlled manner: an initial wave of HBC-derived neurogenesis was observed soon after birth, and a second wave of neurogenesis was observed at 4 months of age. We show that even during normal neuronal turnover, HBCs actively generate neuronal and non-neuronal cells throughout adulthood. Here we report a broader spectrum of action for these cells. Recently, mouse horizontal basal cells (HBCs) were identified as stem cells that regenerate olfactory receptor neurons (ORNs) and non-neuronal cell types only after extensive injury of the olfactory epithelium (OE). The mammalian olfactory neuroepithelium provides a unique system for understanding the regulation of neurogenesis by adult neural stem cells. ![]()
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