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Olfactory epithelial horizonal basal cells : an assessment of stem cell candidacy and behavioural regulation in vivo and in vitro

University of British Columbia

In the olfactory epithelium (OE), new olfactory receptor neurons (ORNS) are continually generated throughout mammalian adulthood. Given this substantial neuronal turnover, a stem cell is proposed to reside within the basal compartment of the OE, which generates ORNs on demand when stimulated by changes in its microenvironment. Although previous studies have identified possible candidates for the olfactory stem cell, its exact identity is as yet unknown. We hypothesize that a population o f horizontal basal cells (HBCs), situated upon the basement membrane of the OE, contains stem cells that contribute to olfactory neurogenesis. A major impediment to the study of these cells is the lack of reliable cell surface molecular markers to distinguish them from other OE cell types. By screening a panel of selected clusters of differentiation (CD) antigens, we have identified three new cell surface markers for the HBC population, namely intercellular adhesion molecule -1 (ICAM-1), β₁ integrin and β₄ integrin. Using these markers to characterize the HBC layer following bulbectomy-induced ORN loss, we have provided evidence of stem cell traits in vivo, including proliferative quiescence relative to OE progenitors, response to lesion, and possible molecular heterogeneity within the HBC compartment. In addition, these studies indicate changes in the populational and subcellular distribution of HBC markers upon loss of ORNs, suggesting a role for these adhesion receptors in the regulation of HBC function in addition to highlighting possible molecular similarities to stem cells of other self-renewing tissues. We have developed a method to select for HBCs in vitro using magnetic activated cell sorting (MACS) and by exploiting their expression of ICAM-1. Using in vitro colony-forming analyses, we obtained evidence that the ICAM-1+ population is enriched for progenitor activity. Further, the efficiency of colony formation can be modulated in vitro by growth factors and adhesive substrates. Lastly, immunohistochemical analysis demonstrated that globose basal cell (GBC) progenitors, ORNs and olfactory ensheathing glia (OEGs) are generated by the ICAM-1+ fraction in clonal culture. Based on these results, we conclude that ICAM-1+ HBCs contribute to the progenitor cell compartment, possibly as stem cells, during olfactory neurogenesis and that the function of these cells may be modulated via adhesion and growth factor signaling by components resident within their in vivo microenvironment.

Thesis/Dissertation

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2009-08-20

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http://hdl.handle.net/2429/12405

Neuroscience

University of British Columbia

UBCV

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