Related Experiment Videos
Development of intercellular junctions in the pulmonary epithelium of the foetal lamb
Insights
Epithelial tight junctions in fetal lamb lungs develop early, becoming structurally continuous and functionally
Area of Science:
- Developmental Biology
- Cell Biology
- Pulmonary Medicine
Background:
- Epithelial tight junctions are crucial for maintaining lung liquid composition and preventing protein leakage in fetal mammalian lungs.
- Understanding the development of these junctions is key to understanding lung maturation and function.
Purpose of the Study:
- To investigate the developmental timeline of intercellular tight junctions in the lining epithelium of fetal lamb lungs.
- To correlate structural development with functional tightness during gestation.
Main Methods:
- Light and electron microscopy, including thin sections and freeze-fracture replicas, were used to examine junctional structures.
- Analysis focused on the number and arrangement of particles and strands in tight junctions throughout gestation.
Main Results:
- Discontinuous tight junctions were observed as early as 39 days of gestation.
- By 76 days to term, junctions resembled adult lungs with continuous networks of strands.
- The epithelium became functionally 'tight' from 69 days onwards, with structural continuity preceding this.
Conclusions:
- Fetal lamb lung epithelium exhibits structurally continuous and functionally tight junctions early in development.
- These tight junctions, along with desmosomes and gap junctions, play vital roles in lung development, ion/water transport, and cellular integrity.
Abstract:
The integrity of epithelial tight junctions in foetal mammalian lungs is essential to maintain the unique ionic composition of lung liquid, and to prevent leakage of serum proteins into peripheral air spaces. In the present study the development of intercellular junctions of the lining epithelium of foetal lamb lungs during gestation was examined by light and electron microscopy. Both thin sections and freeze-fracture replicas were examined by electron microscopy. By 39 days of gestation, epithelial tight junctions consist of a minimum of 3.1 +/- 1.6 (s.D.) and a maximum of 5.8 +/- 2.0 discontinuous rows of particles and short segments of strands on P face ridges and in complementary E face grooves, while from 58 to 76 days they are composed of a network of 4.3 +/- 1.6 to 7.7 +/- 1.9 focally interrupted P face strands. Complementary replicas show that many of the discontinuities on the P face are due to separation of junctional particles on to the E face during fracturing, and not to an absence of junctional particles. From 76 days to term, epithelial tight junctions (exclusive of upper airway epithelium which was not examined) resemble those of adult lungs, and consist of a continuous network of 4.5 +/- 2.0 to 7.5 +/- 2.5 P face strands and complementary particle-free grooves. Permeability measurements, published elsewhere, indicate that the epithelium is functionally 'tight' from 69 days onwards. Tight junctions in peripheral air-space epithelium, therefore, are structurally continuous and functionally 'tight' early in foetal lung development, and form seals at one end of long, narrow intercellular spaces; these features may be important for coupled ion and water transport. When the bounding epithelial cells become flattened, these narrow intercellular spaces remain intact as a result of complex interdigitations of adjacent cell membranes. Desmosomes were present throughout gestation near the abluminal side of the tight junctions and occasionally near the base of the intercellular space. These junctions may serve to connect cells to each other at a time when tight junctions may be mechanically weak. In addition, gap junctions are associated with tight junctions from the glandular through the canalicular stages of lung development. They disappear by 120 days when the epithelial cells are differentiated.