Contribution of Polycomb group proteins to olfactory basal stem cell self-renewal in a novel c-KIT+ culture model and in vivo

Abstract

Olfactory epithelium (OE) has a lifelong capacity for neurogenesis due to the presence of basal stem cells. Despite the ability to generate short-term cultures, the successful in vitro expansion of purified stem cells from adult OE has not been reported. We sought to establish expansion-competent OE stem cell cultures to facilitate further study of the mechanisms and cell populations important in OE renewal. Successful cultures were prepared using adult mouse basal cells selected for expression of c-KIT. We show that c-KIT signaling regulates self-renewal capacity and prevents neurodifferentiation in culture. Inhibition of TGFβ family signaling, a known negative regulator of embryonic basal cells, is also necessary for maintenance of the proliferative, undifferentiated state in vitro. Characterizing successful cultures, we identified expression of BMI1 and other Polycomb proteins not previously identified in olfactory basal cells but known to be essential for self-renewal in other stem cell populations. Inducible fate mapping demonstrates that BMI1 is expressed in vivo by multipotent OE progenitors, validating our culture model. These findings provide mechanistic insights into the renewal and potency of olfactory stem cells.

Multiple polycomb epigenetic regulatory proteins are active in normal and regenerating adult olfactory epithelium

“…Given the importance of PRCs in pluripotent stem cells, we hypothesized that PRC2 would be active in the globose basal stem cells (GBCs) of the OE. Here, we used an established culture model to purify and expand undifferentiated GBCs for further analysis . PRC2 protein expression from GBC–derived cultures and from adult OE tissue extracts was compared by Western blot (Fig.…”

“…Olfactory tissue was obtained from adult mice, which were euthanized under deep anesthesia, and nasal septal and turbinate mucosa free of bone was harvested and pooled. Basal cell cultures were prepared following our published protocol . Briefly, tissue was dissociated in collagenase and dispase solution for 15 min, followed by 3 minutes with 0.125% trypsin.…”

“…Recently, epigenetic modifiers such as Polycomb group proteins have been identified as master regulators of renewal and differentiation in embryonic and adult stem cells . Of interest, we have reported recently that the Polycomb protein BMI1 is present in OE cells, suggesting that Polycomb mechanisms are likely to be important in adult OE neurogenesis …”

Olfactory Mucosa Mesenchymal Stem Cells and Biomaterials: A New Combination to Regenerative Therapies after Peripheral Nerve Injury

“…New nerves generate from GBS in the olfactory epithelium, which are guided to their correct position in the olfactory bulb by OECs in the olfactory mucosa. GBCs, derived from HBCs, were initially thought to be the exclusive source of ON and support cells [74] but it is currently known that MSCs are also capable of producing neurons in vitro [75].…”

“…The OM-MSCs were initially identiied from an embryonic rat OM culture [76] and the irst characterization studies evidenced the expression of mesenchymal-speciic markers such as CD90, CD105, STRO-1 and diferentiation into the three main cell lines [74,77]. OM-MSCs have important characteristics such as neural crest origin, high versatility, vast distribution, advantageous localization and are not susceptible to chromosomal abnormalities or tumorigenicity [78].…”