Clonal Dynamics Reveal Two Distinct Populations of Basal Cells in Slow-Turnover Airway Epithelium.

Julie K Watson,Benjamin D Simons,Cédric Blanpain,Emma L Rawlins,Adam C Wilkinson,Marielle Ousset,Aline Wuidart,Berthold Göttgens,Steffen Rulands,Alexandra Van Keymeulen

doi:10.1016/j.celrep.2015.06.011

Abstract

SummaryEpithelial lineages have been studied at cellular resolution in multiple organs that turn over rapidly. However, many epithelia, including those of the lung, liver, pancreas, and prostate, turn over slowly and may be regulated differently. We investigated the mouse tracheal epithelial lineage at homeostasis by using long-term clonal analysis and mathematical modeling. This pseudostratified epithelium contains basal cells and secretory and multiciliated luminal cells. Our analysis revealed that basal cells are heterogeneous, comprising approximately equal numbers of multipotent stem cells and committed precursors, which persist in the basal layer for 11 days before differentiating to luminal fate. We confirmed the molecular and functional differences within the basal population by using single-cell qRT-PCR and further lineage labeling. Additionally, we show that self-renewal of short-lived secretory cells is a feature of homeostasis. We have thus revealed early luminal commitment of cells that are morphologically indistinguishable from stem cells.

Highlights

The mouse trachea contains three major cell types: TRP63+, KRT5+ basal cells (BCs); luminal secretory cells (SecCs, mostly Scgb1a1+ Club/Clara-like cells); and luminal ciliated cells (CCs) (Rock et al, 2010)
Previous population-level lineage tracing using transgenic Tg(KRT5-CreER) mice demonstrated that BCs include self-renewing stem cells involved in tracheal growth, homeostasis, and repair (Rock et al, 2009)
Other repair studies described an early progenitor (EP) cell as a proliferative KRT8+, TRP63À cell derived from BCs and controlled by Notch signaling (Paul et al, 2014; Rock et al, 2011)

Summary

Introduction

The mouse trachea contains three major cell types: TRP63+, KRT5+ basal cells (BCs); luminal secretory cells (SecCs, mostly Scgb1a1+ Club/Clara-like cells); and luminal ciliated cells (CCs) (Rock et al, 2010). Previous population-level lineage tracing using transgenic Tg(KRT5-CreER) mice demonstrated that BCs include self-renewing stem cells involved in tracheal growth, homeostasis (at least for up to 16 weeks), and repair (Rock et al, 2009). It is not known if BCs are a functionally heterogeneous population. An independent study showed that a population of adult BCs ($12% of steady-state total), which express low levels of transcription factors usually found in more differentiated cells, are able to contribute disproportionally to regeneration following injury (Pardo-Saganta et al, 2015). Is there is an engrained proliferative heterogeneity in the steady-state basal layer? If so, what is the lineage relationship of cells within the basal layer, and how do they connect to the luminal compartments? How do distinct subpopulations of BCs function to maintain normal homeostasis?

Results

Discussion

Conclusion