PHENOTYPIC MARKER EXPRESSION DURING FETAL AND NEONATAL DIFFERENTIATION OF RAT TRACHEAL EPITHELIAL-CELLS

The expression of phenotypic markers was examined during fetal and neo natal differentiation of rat tracheal epithelial (RTE) cells. The rat counterpart of human keratin 18 was predominantly found in columnar ce lls in the adult trachea. It was detected in the primordial tracheal e pithelium first seen on gestational day (GD) 12 (term = 21.5 days). St aining 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. Morpholog ically and immunocytochemically identifiable secretory and ciliated ce lls appeared on GD 18. Ciliated cell number slowly rose while secretor y cells increased dramatically on GD 19 through postnatal day 1. The s ecretory granule antigens detected by monoclonal antibodies RTE 9 and 11 were rare in the adult trachea but were highly expressed in virtual ly all of the perinatal secretory cells. In contrast, the epitope dete cted by monoclonal antibody RTE 12, which was present in all adult tra cheal surface secretory cells, did not appear until postnatal day 1 an d slowly increased. These results demonstrate marked shifts in the bio chemical composition of secretory cells during development and postnat al maturation. For the above-mentioned molecules, a similar expression pattern was observed during epithelial regeneration in tracheal graft s (Am. J. Respir. Cell Mol. Biol. 1992; 7:30-41). Pseudostratification of the epithelium and basal cells was first observed on GD 20. Kerati n 14, which is confined to basal cells in the normal adult trachea, wa s not present in the nascent basal cells but appeared after postnatal day 1. In contrast to the present results, during epithelial regenerat ion in tracheal grafts keratin 14 appeared before markers of highly di fferentiated secretory or ciliated cells. Thus, the biochemical sequen ce of cellular differentiation during regeneration did not precisely r ecapitulate development.