Cytodifferentiation of the nonciliated bronchiolar epithelial (Clara) cell during rabbit lung maturation

An ultrastructural and morphometric study

Charles Plopper, Janice L. Alley, Cosette J. Serabjitsingh, Richard M. Philpot

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron‐dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P‐450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0–1 day, 3–4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 x) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minumum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168‐point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60% of the cell cytoplasm), few mitochondria (less than 15%), little granular endoplasmic reticulum (GER) (20%), minimal AER (less than 5%), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20%). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40%), secretory granules, little glycogen (11%), and GER (10%). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.

Original languageEnglish (US)
Pages (from-to)329-357
Number of pages29
JournalAmerican Journal of Anatomy
Volume167
Issue number3
DOIs
StatePublished - Jan 1 1983

Fingerprint

Smooth Endoplasmic Reticulum
Epithelial Cells
Rabbits
Lung
Glycogen
Rough Endoplasmic Reticulum
Secretory Vesicles
Mitochondria
Cell Nucleus Size
Parturition
Glutaral
Xenobiotics
Mixed Function Oxygenases
Transmission Electron Microscopy
Cytochrome P-450 Enzyme System
Cell Differentiation
Cytoplasm
Electrons

ASJC Scopus subject areas

  • Anatomy

Cite this

Cytodifferentiation of the nonciliated bronchiolar epithelial (Clara) cell during rabbit lung maturation : An ultrastructural and morphometric study. / Plopper, Charles; Alley, Janice L.; Serabjitsingh, Cosette J.; Philpot, Richard M.

In: American Journal of Anatomy, Vol. 167, No. 3, 01.01.1983, p. 329-357.

Research output: Contribution to journalArticle

@article{6d5b70614c214a8e8e82951819c0ed33,
title = "Cytodifferentiation of the nonciliated bronchiolar epithelial (Clara) cell during rabbit lung maturation: An ultrastructural and morphometric study",
abstract = "The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron‐dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P‐450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0–1 day, 3–4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 x) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minumum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168‐point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60{\%} of the cell cytoplasm), few mitochondria (less than 15{\%}), little granular endoplasmic reticulum (GER) (20{\%}), minimal AER (less than 5{\%}), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20{\%}). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40{\%}), secretory granules, little glycogen (11{\%}), and GER (10{\%}). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.",
author = "Charles Plopper and Alley, {Janice L.} and Serabjitsingh, {Cosette J.} and Philpot, {Richard M.}",
year = "1983",
month = "1",
day = "1",
doi = "10.1002/aja.1001670305",
language = "English (US)",
volume = "167",
pages = "329--357",
journal = "Developmental Dynamics",
issn = "1058-8388",
publisher = "Wiley-Liss Inc.",
number = "3",

}

TY - JOUR

T1 - Cytodifferentiation of the nonciliated bronchiolar epithelial (Clara) cell during rabbit lung maturation

T2 - An ultrastructural and morphometric study

AU - Plopper, Charles

AU - Alley, Janice L.

AU - Serabjitsingh, Cosette J.

AU - Philpot, Richard M.

PY - 1983/1/1

Y1 - 1983/1/1

N2 - The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron‐dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P‐450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0–1 day, 3–4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 x) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minumum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168‐point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60% of the cell cytoplasm), few mitochondria (less than 15%), little granular endoplasmic reticulum (GER) (20%), minimal AER (less than 5%), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20%). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40%), secretory granules, little glycogen (11%), and GER (10%). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.

AB - The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron‐dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P‐450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0–1 day, 3–4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 x) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minumum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168‐point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60% of the cell cytoplasm), few mitochondria (less than 15%), little granular endoplasmic reticulum (GER) (20%), minimal AER (less than 5%), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20%). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40%), secretory granules, little glycogen (11%), and GER (10%). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.

UR - http://www.scopus.com/inward/record.url?scp=0020520233&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0020520233&partnerID=8YFLogxK

U2 - 10.1002/aja.1001670305

DO - 10.1002/aja.1001670305

M3 - Article

VL - 167

SP - 329

EP - 357

JO - Developmental Dynamics

JF - Developmental Dynamics

SN - 1058-8388

IS - 3

ER -