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Rabbit retinal Müller cells in cell culture show gap and tight junctions which they do not express in situ
H Wolburg1, W Reichelt, J U Stolzenburg
1Institute of Pathology, University of Tübingen, F.R.G.
Abstract:
Retinae of early postnatal rabbits were enzymatically dissociated and explanted in a culture system. The prospective myelinated region was discarded in order to avoid the presence of astrocytic or mesenchymal cells. After about 14 days in vitro (DIV), outgrowing glial (Müller) cells formed what light optically appeared to be confluent monolayers but by electron microscopy was shown to consist of flat epithelioid cells which overlapped considerably by extension of cytoplasmic tongues. Applying the freeze-fracture technique, apposed membranes of these cells were demonstrated to express infrequently but consistently both gap and tight junctions. This kind of junctions has never been observed on the membrane of rabbit Müller cells in situ. In comparison with Müller cell membranes in situ, the density of intramembrane particles was considerably reduced. Orthogonal arrays of particles which are characteristic elements of Müller cells in situ were not detected. Our results suggest that in homogeneous cell culture, Müller cells form some kind of epithelium-like specialized intercellular junctions. This situation resembles that of closely related glial cell types which form homogeneous layers in situ as e.g. retinal pigment epithelium cells expressing tight junctions, and marginal astrocytes being coupled by extensive gap junctions.
Insights
Rabbit Müller cells in culture form specialized epithelium-like junctions, including gap and tight junctions, not seen in their natural state. This suggests in vitro conditions induce unique intercellular communication in these retinal glial cells.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- Müller cells are the primary glial cells in the vertebrate retina.
- Their function and intercellular communication in vivo are well-studied.
- Understanding Müller cell behavior in vitro is crucial for regenerative medicine and disease modeling.
Purpose of the Study:
- To investigate the intercellular junction formation of rabbit Müller cells in a homogeneous cell culture system.
- To compare the in vitro junctional characteristics with those observed in situ.
- To explore the potential for Müller cells to form epithelium-like structures in culture.
Main Methods:
- Enzymatic dissociation and explantation of early postnatal rabbit retinal cells.
- Selective culture of Müller cells, excluding myelinated regions.
- Freeze-fracture electron microscopy to analyze cell membrane junctions.
- Light and electron microscopy for morphological characterization.
Main Results:
- Cultured Müller cells formed confluent monolayers with overlapping epithelioid cells.
- Freeze-fracture revealed infrequent but consistent gap and tight junctions between apposed Müller cell membranes.
- These junctions were not observed in Müller cells in situ.
- Reduced intramembrane particle density and absence of orthogonal arrays were noted compared to in situ cells.
Conclusions:
- Rabbit Müller cells in homogeneous culture develop specialized, epithelium-like intercellular junctions.
- These findings suggest that in vitro conditions can induce novel junctional complexes in Müller cells.
- The observed junctions resemble those found in other glial cells forming homogeneous layers in situ, like retinal pigment epithelium and astrocytes.