Neuroepithelial body microenvironment is a niche for a distinct subset of Clara-like precursors in the developing airways

Abstract

Clara cells of mammalian airways have multiple functions and are morphologically heterogeneous. Although Notch signaling is essential for the development of these cells, it is unclear how Notch influences Clara cell specification and if diversity is established among Clara cell precursors. Here we identify expression of the secretoglobin Scgb3a2 and Notch activation as early events in a program of secretory cell fate determination in developing murine airways. We show that Scgb3a2 expression in vivo is Notch-dependent at early stages and ectopically induced by constitutive Notch1 activation, and also that in vitro Notch signaling together with the pan-airway transcription factor Ttf1 (Nkx2.1) synergistically regulate secretoglobin gene transcription. Furthermore, we identified a subpopulation of secretory precursors juxtaposed to presumptive neuroepithelial bodies (NEBs), distinguished by their strong Scgb3a2 and uroplakin 3a ( Upk3a ) signals and reduced Ccsp (Scgb1a1) expression. Genetic ablation of Ascl1 prevented NEB formation and selectively interfered with the formation of this subpopulation of cells. Lineage labeling of Upk3a -expressing cells during development showed that these cells remain largely uncommitted during embryonic development and contribute to Clara and ciliated cells in the adult lung. Together, our findings suggest a role for Notch in the induction of a Clara cell-specific program of gene expression, and reveals that the NEB microenvironment in the developing airways is a niche for a distinct subset of Clara-like precursors.

Notch3-Jagged signaling controls the pool of undifferentiated airway progenitors

“…5B). We could not detect expression of Dll ligands other than in neuroendocrine cells using in situ hybridization (Guha et al, 2012). We asked whether these Jag ligands contributed equally to mediate the Notch effects in restricting the pool of the p63+ cell population.…”

Plasticity in the lung: making and breaking cell identity

“…1) (Guha et al, 2012). Secretory cells that express Upk3a are present immediately adjacent to PNECs, and these cells are thought to represent the variant club cells (Guha et al, 2012;Hong et al, 2001) (Fig. 2B).…”

“…PNECs are marked by the expression of CGRP (calcitonin gene-related peptide; CALCA), chromogranin A and ASCL1 (achete-scute homolog 1) and are present in mouse in both large and small airways and are enriched at the branch points of airways (Guha et al, 2012;Reynolds et al, 2000b;Song et al, 2012). They derive from the same tip progenitors that produce the other epithelial cell types during branching morphogenesis.…”

“…More recently, these subsets of secretory cells were prospectively identified based on the presence or absence of expression of Upk3a, a family member of the uroplakin proteins with unknown function in the lung ( Fig. 1) (Guha et al, 2012). Secretory cells that express Upk3a are present immediately adjacent to PNECs, and these cells are thought to represent the variant club cells (Guha et al, 2012;Hong et al, 2001) (Fig.…”

Functional expression of the multimodal extracellular calcium-sensing receptor in pulmonary neuroendocrine cells

“…Apart from its potential role in the physiology of NEB cells, it might also be worthwhile to consider a role for the CaSR as a more general [Ca 2+ ] o sensor in the NEB microenvironment, which is now believed to be a potential stem cell niche in the epithelium of intrapulmonary airways (Bishop, 2004;Giangreco et al, 2007;Guha et al, 2012;Liu et al, 2006;Rawlins and Hogan, 2006;Snyder et al, 2009). Several signaling pathways involved in cell growth and differentiation, adult stem cell proliferation and specification, have been reported to be highly influenced by changes in [Ca 2+ ] o through the CaSR (Riccardi and Kemp, 2012).…”