Structural Development, Cellular Differentiation and Proliferation of the Respiratory Epithelium in the Bovine Fetal Lung

Abstract

Fetal bovine lung samples of 11 different gestational ages were assigned to a classical developmental stage based on histological morphology. Immunohistochemistry was used to characterize the morphology of forming airways, proliferation rate of airway epithelium and the presence of epithelial cell types (i.e. ciliated cells, club cells, neuroepithelial cells (NECs) and type II pneumocytes). Typical structural organization of pseudoglandular (84-98 days gestational age [DGA]), canalicular (154-168 DGA) and alveolar (224-266 DGA) stages was recognized. In addition, transitional pseudoglandular-canalicular (112-126 DGA) and canalicular-saccular (182 DGA) morphologies were present. The embryonic stage was not observed. A significantly (P <0.05) higher proliferation rate of pulmonary epithelium, on average 5.5% and 4.4% in bronchi and bronchioles, respectively, was present in the transitional pseudoglandular-canalicular phase (112-126 DGA) compared with all other phases, while from 8 weeks before term (224-266 DGA) proliferation had almost ceased. The first epithelial cells identified by specific marker proteins in the earliest samples available for study (84 DGA) were ciliated cells and NECs. Club cells were present initially at 112 DGA and type II pneumocytes at 224 DGA. At the latest time points (224-226 DGA) these latter cell types were still present at a much lower percentage compared with adult cattle. This study characterized bovine fetal lung development by histological morphology and cellular composition of the respiratory epithelium and suggests that the apparent structural anatomical maturity of the bovine lung at term is not matched by functional maturity of the respiratory epithelium.

Qualitative and quantitative ultrasound attributes of maternal‐foetal structures in pregnant ewes

“…During the canicular phase of pulmonary development, a period that involves the formation of bronchioles, alveolar ducts, primitive alveoli, vascular tissue, type I and type II pulmonary cell differentiation, pulmonary surfactant proteins and alveolar-capillary barrier (Joshi & Kotecha, 2007), it was found a decrease in echogenicity and mean NVPs of foetal lung tissue from ovine foetuses. Probably, this change in echogenicity is related to the formation of the mentioned tissues, the beginning of the alveolar structures filling by the foetal lung fluid, responsible for keeping the spaces distended, limiting the entry of amniotic fluid and allowing the growth and structural maturation of this tissue (Drozdowska, Cousens, Finlayson, Collie, & Dagleish, 2016;Harding & Hooper, 1996;Hooper & Harding, 1995).…”

Transcriptomic profiling reveals disordered regulation of surfactant homeostasis in neonatal cloned bovines with collapsed lungs and respiratory distress

“…Immunohistochemistry was performed following previously described protocols (Drozdowska, Cousens, Finlayson, Collie, & Dagleish, ). Lung tissue samples fixed in 4% paraformaldehyde were embedded in paraffin and sectioned.…”

“…Immunohistochemistry was performed following previously described protocols (Drozdowska, Cousens, Finlayson, Collie, & Dagleish, 2016 were used; both of these primary antibodies are polyclonal, and crossreacted with bovine proteins. Secondary horseradish peroxidase-conjugated goat-anti-rabbit IgG (1:50 dilution of A0208) (Beyotime, Shanghai, China) and 3,3′-diaminobenzidine was used for detection.…”

Neonatal respiratory distress syndrome and underlying mechanisms in cloned cattle

“…Histopathology was performed as described previously (Drozdowska, Cousens, Finlayson, Collie, & Dagleish, 2016). Lung tissue samples in 4% paraformaldehyde were embedded in paraffin, cut into 4-µm-thick slices, and stained with hematoxylin-eosin for microscopic examination.…”

“…Immunostaining was performed according to an earlier report (Drozdowska et al, 2016). Detailed information on the antibodies and dilutions are provided in Table 3.…”