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Ultrastructural localization of carbohydrates in Reichert's membrane of the mouse
Abstract:
In the present investigation, we examined the role of trophoblast and parietal endoderm cells in the synthesis of carbohydrate-containing components of Reichert's membrane. To eliminate the function of Reichert's membrane as a filter between maternal and embryonal tissues we carried out our examination under in vitro conditions. Parietal yolk sac from mouse embryos on day 9 post coitum (p.c.) were cultivated for 0 to 5 days. Because tannic acid enables a complex formation between carbohydrates and osmium we chose the fixation with this acid for the ultrastructural study. Electron microscopy showed that for assembly of Reichert's membrane, trophoblast cells produce and then release components that were detected as tannic acid-positive granules both in the Reichert's membrane and in the vacuoles of the trophoblast cells. To localize specific carbohydrates we used postembedding-gold-lectin histochemistry on LR-GoldR-embedded tissues. Strong binding sites for the lectins WGA (Triticum vulgare), RCA I (Ricinus communis) and Con A (Canavalia ensiformis) were observed in Reichert's membrane and trophoblast cells but not in the parietal endoderm cells. The LTA (Lotus tetragonolobus)-binding pattern was positive in the membrane and its adjacent cells but that of the LFA (Limax flavus) was negative in the parietal endoderm cells and very weak in Reichert's membrane and trophoblast cells. Our results demonstrate that trophoblast cells are involved in the construction of Reichert's membrane through the production and release of specific glycoconjugates.
Insights
Trophoblast cells synthesize and release components essential for building Reichert's membrane, a key structure in early embryonic development. This study clarifies the glycoconjugate contribution of trophoblast cells to Reichert's membrane formation.
Area of Science:
- Developmental Biology
- Cell Biology
- Extracellular Matrix Biology
Background:
- Reichert's membrane is a crucial extracellular matrix layer in early mammalian development, separating maternal and embryonic tissues.
- The precise cellular origins of Reichert's membrane components, particularly its carbohydrate-rich elements, remain incompletely understood.
Purpose of the Study:
- To investigate the roles of trophoblast and parietal endoderm cells in synthesizing the carbohydrate-containing components of Reichert's membrane.
- To elucidate the cellular mechanisms underlying Reichert's membrane assembly in vitro.
Main Methods:
- Cultured mouse parietal yolk sacs (day 9 p.c.) were utilized for in vitro examination over 0-5 days.
- Ultrastructural analysis employed tannic acid fixation for carbohydrate-osmium complex formation.
- Post-embedding gold-lectin histochemistry (WGA, RCA I, Con A, LTA, LFA) was used to localize specific carbohydrates.
Main Results:
- Electron microscopy revealed tannic acid-positive granules in Reichert's membrane and trophoblast cell vacuoles, indicating trophoblast-derived components.
- Lectins WGA, RCA I, and Con A showed strong binding in Reichert's membrane and trophoblast cells, but not parietal endoderm.
- LTA binding was observed in the membrane and adjacent cells, while LFA binding was weak or negative in parietal endoderm and Reichert's membrane.
Conclusions:
- Trophoblast cells actively produce and secrete specific glycoconjugates that contribute to the structural integrity of Reichert's membrane.
- Parietal endoderm cells appear to play a minimal role in the synthesis of the specific glycoconjugates examined in Reichert's membrane.