Directed Migration of Pulmonary Neuroendocrine Cells toward Airway Branches Organizes the Stereotypic Location of Neuroepithelial Bodies

Abstract

The airway epithelium consists of diverse cell types, including neuroendocrine (NE) cells. These cells are thought to function as chemoreceptors and as a component of the stem cell niche as well as the cells of origin in small-cell lung cancer. NE cells often localize at bifurcation points of airway tubes, forming small clusters called neuroepithelial bodies (NEBs). To investigate NEB development, we established methods for 3D mapping and ex vivo 4D imaging of developing lungs. We found that NEBs localize at stereotypic positions in the bifurcation area irrespective of variations in size. Notch-Hes1 signaling contributes to the differentiation of solitary NE cells, regulating their number but not localization. Live imaging revealed that individual NE cells migrate distally to and cluster at bifurcation points, driving NEB formation. We propose that NEB development is a multistep process involving differentiation of individual NE cells and their directional migration to organize NEBs.

Epithelial cell behaviours during neurosensory organ formation

“…The cell has directed motility, i.e. it migrates, and this occurs within the epithelium of origin (intraepithelially) (Kuo and Krasnow, 2015;Noguchi et al, 2015;Soulika et al, 2016). It is currently unclear to what extent a slithering cell shares similar molecular characteristics with cohorts of cells undergoing EMT (see below).…”

“…NEBs grow in centrifugal orientation, i.e. NE cell differentiation occurs from the proximal to the distal part of the branchpoint (Avadhanam et al, 1997;Hoyt et al, 1990;Noguchi et al, 2015), and they are highly innervated.…”

“…For example, it has been shown that NE cells express Ascl1 and Delta1 (Dll1), and are surrounded by cells (termed SPNC cells) with active Notch signalling (Noguchi et al, 2015). When SPNC cells are selectively eliminated, the number of NE cells remains unaffected, showing that these cells with Notch activity do not contribute to the NE cell fate.…”

“…When SPNC cells are selectively eliminated, the number of NE cells remains unaffected, showing that these cells with Notch activity do not contribute to the NE cell fate. However, when Notch signalling is abrogated (via conditional inactivation of the Notch effector Hes1) in the epithelium that generates NE cells, the number of NE cells is dramatically increased and NEB clusters are enlarged, suggesting that Notch/Hes1 signalling restricts NE cell fate in epithelial progenitors through a lateral inhibition mechanism (Noguchi et al, 2015).…”

“…Apoptosis has also been excluded as a mechanism of NEB spacing (Kuo and Krasnow, 2015). By contrast, using in vivo imaging in slice cultures and in air-liquid organ cultures, it has been shown that NE cells are motile (Kuo and Krasnow, 2015;Noguchi et al, 2015). These studies revealed that, as they 'slither', NE progenitors extend long cytoplasmic projections, detach from the basement membrane, take perpendicular positions relative to surrounding epithelial cells, and crawl over and around epithelial cells for tens of microns.…”