Horizontal Basal Cells Research Articles

Cell cycle of globose basal cells in rat olfactory epithelium

The olfactory epithelium of adult mammals has the unique property of generating olfactory sensory neurons throughout life. Cells of the basal compartment, which include horizontal and globose basal cells, are responsible for the ongoing process of neurogenesis in this system. We report here that the globose basal cells in olfactory epithelium of rats, as in mice, are the predominant type of proliferating cell, and account for 97.6% of the actively dividing cells in the basal compartment of the normal epithelium. Globose basal cells have not been fully characterized in terms of their proliferative properties, and the dynamic aspects of neurogenesis are not well understood. As a consequence, it is uncertain whether cell kinetic properties are under any regulation that could affect the rate of neurogenesis. To address this gap in our knowledge, we have determined the duration of both the synthesis phase (S-phase) and the full cell cycle of globose basal cells in adult rats. The duration of the S-phase was found to be 9 hr in experiments utilizing sequential injections of either IdU followed by BrdU or 3H-thy followed by BrdU. The duration of the cell cycle was determined by varying the time interval between the injections of 3H-thy and BrdU and tracking the set of cells that exit S shortly after the first injection. With this paradigm, the interval required for these cells to traverse G2, M, G1, and a second S-phase, is equivalent to the duration of one mitotic cycle and equals 17 hr. These observations serve as the foundation to assess whether the cell cycle duration is subject to regulation in response to experimental injury, and whether such regulation is partly responsible for changes in the rate of neurogenesis in such settings.

Globose basal cells are neuronal progenitors in the olfactory epithelium: A lineage analysis using a replication-incompetent retrovirus

We have used a replication-incompetent retrovirus to analyze the lineage of olfactory receptor neurons in young rats. At 5–40 days after infection, clusters of infected cells comprised two major types: one consisted of 1–2 horizontal basal cells, and a second consisted of variable numbers of globose basal cells and immature and mature sensory neurons. Olfactory nerve lesion (which enhances neuronal turnover) increased the frequency of the globose-sensory neuron clusters as well as the number of cells in such clusters. No clusters contained both horizontal and globose basal cells, and none contained sustentacular cells. These data suggest, at least in young rats, that horizontal basal cells are not precursors of olfactory neurons, that there is a lineage path from globose cells to mature neurons, and that sustentacular cells may arise from a separate lineage.

Lineage analysis of the olfactory epithelium using a replication-incompetent retrovirus.

We have analysed the lineage of olfactory receptor neurons using a replication-incompetent retrovirus injected beneath the olfactory epithelium of young rats. There are two major types of clusters of infected cells seen at 5--40 days after infection: (i) horizontal basal cells (HBCs); (ii) variable numbers of globose basal cells (GBCs), and immature and mature sensory neurons. Olfactory nerve lesion increased the frequency of the globose/sensory neuron clusters, as well as the number of cells/cluster, but did not change the number of HBC clusters or cells/cluster. No clusters contained sustentacular cells. These data indicate that, at least in young rats: (i) HBCs are not precursors of olfactory neurons; (ii) there is a lineage path from GBCs to mature neurons; and (iii) sustentacular cells arise from a separate lineage.

Characterization of potential precursor populations in the mouse olfactory epithelium using immunocytochemistry and autoradiography

There are at least two basal cell populations in the olfactory epithelium that could give rise to olfactory neurons during development, in the normal adult, and after experimentally induced receptor cell death. These populations have been subdivided as horizontal (HBC) and globose (GBC) basal cells on the basis of morphological criteria and by staining with antibodies against cytokeratin. HBCs are positive for cytokeratin while GBCs are negative. We have studied which cell type is induced to divide during receptor cell regeneration stimulated by olfactory bulbectomy using a combination of immunocytochemistry and autoradiography. By examining which population increases its labeling index with 3H-thymidine (3H-TdR) at various times after bulbectomy, it is shown that there is an increase in 3H-TdR uptake in the cytokeratin-negative GBCs with no change in the cytokeratin-positive HBCs. This suggests that the GBCs are specifically induced to divide in response to cues that accompany receptor cell death, and it is thus concluded that these cells are among the precursors of new olfactory receptor neurons.