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Tight junctions and cavitation in the human pre-embryo
R Gualtieri1, L Santella, B Dale
1Stazione Zoologica, Naples, Italy.
Molecular Reproduction and Development
|May 1, 1992
Summary
Tight junctions, or zonulae occludentes, form early in human morula development, sealing off developing cavities. These structures are crucial for blastocoele formation in early human embryos.
Area of Science:
- Developmental Biology
- Cell Biology
- Human Embryology
Background:
- Early human embryonic development involves significant cellular reorganization and specialization.
- The formation of the blastocoele, a key cavity in the blastocyst, is essential for implantation and subsequent development.
- Understanding the establishment of cell junctions and cavities is critical for reproductive biology.
Purpose of the Study:
- To investigate the initial formation and localization of tight junctions (zonulae occludentes) during human morula and early blastocyst development.
- To explore the relationship between intracellular/extracellular cavities, polygranules, and the development of trophectoderm.
- To elucidate potential mechanisms underlying blastocoele formation.
Main Methods:
- Transmission electron microscopy was used to examine human morula and early blastocyst stages.
- Lanthanum tracer was employed to assess the permeability and sealing capacity of developing cell junctions.
- Ultrastructural analysis focused on cell apposition, junctional complexes, vacuoles, and cavities.
Main Results:
- Tight junctions (zonulae occludentes) were identified between all cell pairs in the human morula, associated with microfilaments.
- Lanthanum tracer revealed the initial assembly of zonulae occludentes in cavitating morula, preventing tracer entry into nascent cavities.
- Presumptive trophectoderm cells exhibited vacuoles and cavities containing electron-dense polygranules, potentially indicating a common origin. These were absent in early blastocyst trophectoderm, with zonulae occludentes located apically.
Conclusions:
- Zonulae occludentes assemble early in human embryogenesis, establishing epithelial barriers crucial for blastocoele formation.
- The presence and characteristics of vacuoles and polygranules in early embryonic cells suggest their involvement in cavity formation.
- The apical localization of zonulae occludentes in early blastocyst trophectoderm supports their role in blastocoele expansion and maintenance.