Phenotypic Marker Expression during Fetal and Neonatal Differentiation of Rat Tracheal Epithelial Cells

Abstract

The expression of phenotypic markers was examined during fetal and neonatal differentiation of rat tracheal epithelial (RTE) cells. The rat counterpart of human keratin 18 was predominantly found in columnar cells in the adult trachea. It was detected in the primordial tracheal epithelium first seen on gestational day (GD) 12 (term = 21.5 days). Staining intensity gradually increased, and by GD 17 it was principally localized to the apical portion of the epithelium. The rat counterpart of human keratin 19 was barely detectable in the trachea on GD 13 but became abundant in almost all RTE cells on and after GD 19. Morphologically and immunocytochemically identifiable secretory and ciliated cells appeared on GD 18. Ciliated cell number slowly rose while secretory cells increased dramatically on GD 19 through postnatal day 1. The secretory granule antigens detected by monoclonal antibodies RTE 9 and 11 were rare in the adult trachea but were highly expressed in virtually all of the perinatal secretory cells. In contrast, the epitope detected by monoclonal antibody RTE 12, which was present in all adult tracheal surface secretory cells, did not appear until postnatal day 1 and slowly increased. These results demonstrate marked shifts in the biochemical composition of secretory cells during development and postnatal maturation. For the above-mentioned molecules, a similar expression pattern was observed during epithelial regeneration in tracheal grafts (Am. J. Respir. Cell Mol. Biol. 1992; 7:30-41). Pseudo-stratification of the epithelium and basal cells was first observed on GD 20. Keratin 14, which is confined to basal cells in the normal adult trachea, was not present in the nascent basal cells but appeared after postnatal day 1. In contrast to the present results, during epithelial regeneration in tracheal grafts keratin 14 appeared before markers of highly differentiated secretory or ciliated cells. Thus, the biochemical sequence of cellular differentiation during regeneration did not precisely recapitulate development.

Critical role of p63 in the development of a normal esophageal and tracheobronchial epithelium

“…4B) and sporadically and weakly for K14, K5, and BS-I-B4 ( Fig. 4D and data not shown) but began to stain more intensely for K14, K5, and BS-I-B4 after birth, in agreement with findings described in previous reports (49). In adult mice as well as in humans, the tracheobronchial lining consists of a pseudostratified epithelium containing ciliated, basal, and mucosecretory cells.…”

“…They distinguish themselves from basal cells in the adult esophagus in that they do not express K14 (Fig. 1C) and do not bind BS-I-B4 (not shown), which are markers for basal cells (14,16,21,48,49). The p63 Ϫ cells in the upper layers may represent preciliated cells, because these cells stain weakly for the ciliated cell marker ␤-tubulin IV (Fig.…”

“…8, models A and B). In both epithelia, these stem cells have the capacity to differentiate into ciliated cells (p63 Ϫ /TubIV ϩ ), which are the first differentiated cells to appear during development, and secretory cells (49). Later, at or shortly after birth, the basally located cells begin to express increasing levels of K14 and K5 and to stain for BS-I-B4, as Randell et al (49) also observed, suggesting that they are gradually differentiating into mature (p63 ϩ /K14 ϩ /K5 ϩ /BS-I-B4 ϩ ) basal cells (Fig.…”

“…During development, stem cells first differentiate into ciliated (p63 Ϫ /␤-tubulin IV ϩ ) and secretory cells and later, at birth, begin to differentiate into basal cells (p63 ϩ /K14 ϩ /K5 ϩ /BS-I-B4 ϩ ), thereby generating a pseudostratified epithelium (Fig. 4, A and C) (49). Similarly to basal cells in the esophagus, the basal cells in the tracheal epithelium of newborn mice stained strongly for p63 (Fig.…”

“…TBE cells in culture exhibit many characteristics of basal cells, including the abundant presence of tonofilaments and the expression of K5 and K14 (Figs. 5 and 6) (14,21,24,49). In the presence of retinoids, these cells can be induced to undergo normal differentiation into mucous-secreting and ciliated cells (27,51).…”