Temporal and spatial distribution of ciliogenesis in the tracheobronchial airways of mice

Abstract

Little is known about ciliogenesis as it proceeds through the entire airway tree, from the trachea to the terminal bronchioles, especially during the postnatal period. The purpose of this study was to define the spatial and temporal (prenatal and postnatal) pattern of normal cilia development in the mouse. Three airway generations representing the entire airway tree were examined: trachea, lobar bronchi, and terminal bronchiole. Ciliated cells in lung lobe whole mounts were labeled with a fluorescent dye for confocal microscopy, and ciliated cell surface density was measured for each airway generation and age. The same samples were examined by scanning electron microscopy to verify the appearance of ciliated cells among the differentiating epithelium of the airways. Ciliated cells were first detected in the trachea and lobar bronchi at 16 days gestational age (DGA) and in the terminal bronchioles at 18 DGA. Ciliated cell surface density increased with prenatal and postnatal age at all airway levels. However, the ciliated cell surface density of the trachea and lobar bronchi was always greater compared with the terminal bronchiole. In conclusion, the study revealed that in developing tracheobronchial airways of the mouse: 1) Ciliogenesis differs temporally and spatially by airway generation; 2) Ciliated cell surface density increases with age in all airway generations, but density decreases in a proximal to distal direction; and 3) A significant portion of ciliogenesis continues after birth. This study provides a healthy basis for investigations of neonatal pulmonary disease or pollutant toxicity affecting cilia and its functions.

Lung development and repair: Contribution of the ciliated lineage

“…E16.5 was the first time that we detected, by immunohistochemistry, the neuroendocrine cell marker CGRP (calcitonin gene-related peptide). It was also the first time, in agreement with other studies, when surface cilia were detected, using antibodies to ␤-tubulin (6,30). It was now possible to observe, as previously described in human embryonic lung samples, that some of the CGRP ϩ neuroendocrine bodies are surrounded by Scgb1a1 ϩ Clara precursors, whereas others are ringed by a mixture of ciliated and Clara precursor cells (31).…”

“…As the tubes extend, descendants of these cells give rise to the progenitors of the major cell types of the conducting airways-certainly to the ciliated and secretory (Clara) cells (5). The appearance of morphologically differentiated epithelial cells begins proximally and proceeds distally (6,7). We need to know a great deal more about the steps involved in generating these differentiated cells: the identity of intermediate cell types, whether these intermediates self renew as transit amplifying populations, their lineage relationships, and the precise mechanism of their commitment to different fates.…”

The deubiquitinating enzyme CYLD controls apical docking of basal bodies in ciliated epithelial cells

“…We next examined motile cilia formation in trachea of WT and Cyld D932 E18.5 embryos from several litters by scanning electron microscopy. As ciliogenesis in the trachea occurs proximo-distally 29 , we imaged and counted the ciliated cells in every field from the larynx to the beginning of the main bronchi to avoid bias due to spatial differences. For each litter, the number of multiciliated cells was at least 50% lower in the mutants than in WT embryos.…”

The building blocks of mammalian lung development

“…1C,D). The epithelial composition of the bronchioles, particularly the ratio of Clara:ciliated cells, changes stereotypically along the proximal-distal axis; the smaller airways having an increased proportion of Clara cells (Toskala et al, 2005). The bronchioles are completely circled by parabronchial smooth muscle and do not have cartilage (Fig.…”

“…Directly testing this hypothesis will require a better understanding of the molecular mechanisms which are responsible for cell fate specification in the developing lung. Differentiation of the airway epithelium has been observed to move down the airways from the proximal to the more distal regions (McDowell et al, 1994;Toskala et al, 2005). Molecular markers for NE cell fate specification (for example, the transcription factor Ascl1) and Clara and ciliated cell differentiation (Secretoglobin1a1 and the transcription factor Foxj1) are first observed at E12.5 (NE cells) and E14.5, or 15.5 (ciliated and Clara cells), always at least one airway generation from the multipotent progenitors in the distal tip (Rawlins et al, 2007;McGovern et al, 2010).…”