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The fine structure of polychaete septate junctions
Cell and Tissue Research
|October 22, 1976
Summary
Septate junctions in marine annelids like Nereis sp. show complex structures. Lanthanum tracer reveals intricate details, suggesting shared features across invertebrate septate junction types.
Area of Science:
- Marine biology
- Cell biology
- Invertebrate zoology
Background:
- Epidermal septate junctions are crucial for invertebrate tissue integrity.
- Previous studies show varied structures of septate junctions in different species.
- The precise architecture of these junctions remains incompletely understood.
Purpose of the Study:
- To elucidate the detailed ultrastructure of epidermal septate junctions in Nereis sp. and Cirriformia sp.
- To investigate the role of fixation and tracer techniques in visualizing junctional morphology.
- To compare the observed structures with known types of invertebrate septate junctions.
Main Methods:
- Transmission electron microscopy (TEM) using OsO4 or glutaraldehyde/OsO4 fixation.
- Utilizing lanthanum as an extracellular tracer to delineate junctional clefts.
- Analysis of junctional morphology in transverse, oblique, and en face sections.
Main Results:
- Septate junctions exhibit variable appearances depending on sectioning orientation and fixation.
- Septa are characterized by an electron-lucent center and appear linked by arms, forming a honeycomb pattern in en face views.
- Lanthanum tracer revealed a chain-like lattice within the junctional cleft and intricate septal substructure, indicating limited permeability.
Conclusions:
- The studied septate junctions possess complex, intricate substructures not easily resolved by standard TEM.
- Observed features suggest a degree of structural homology across different types of invertebrate septate junctions.
- Further high-resolution imaging techniques may be needed to fully resolve the junctional architecture.