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Concomitant changes in endothelial cell junctions and extracellular matrix components in the chick embryo aorta
E Arciniegas1, F Sánchez, D Candelle
1Instituto Anatomopatológico, Facultad de Medicina, Universidad Central de Venezuela, Caracas.
Insights
Chick embryo aorta development involves forming intercellular junctions and complex extracellular matrix, influencing endothelial cell polarization. This study tracks these changes from day 7 to post-hatching.
Area of Science:
- Developmental Biology
- Cell Biology
- Histology
Background:
- Endothelial activation and collagen response in chick embryos are known between days 7-18.
- This response diminishes significantly after hatching.
Purpose of the Study:
- To investigate the development of intercellular junctions and extracellular matrix in chick embryo aortas.
- To understand how these changes influence endothelial cell polarization.
Main Methods:
- Freeze-fracturing technique to analyze endothelial cell membranes.
- Histochemical staining with cuprolinic blue to study proteoglycans.
- Analysis of aortas from chick embryos (days 7-21) and post-hatching chicks (14 days).
Main Results:
- Intramembranous particle aggregation suggests gap junction formation between days 12-14.
- Development of linear and macular tight junctions observed, indicating increasing occlusion.
- Complex extracellular matrix with proteoglycans forms in the subendothelial region.
Conclusions:
- Intercellular junction assembly progresses from linear to macular and occluding arrangements.
- Increasing extracellular matrix complexity correlates with junction development.
- These combined changes likely influence endothelial cell polarization in developing chick aortas.
Abstract:
According to previous studies, a process of endothelial activation seems to be occurring in the chick embryo between days 7 and 18. Also, endothelial cells respond to collagen as a substratum between 12 and 18 days, and this response diminishes until it almost disappears after birth. In the present study, aortas from chick embryos (days 7 to 21), and from chicks (14 days posthatching) were used. The results obtained by the freeze-fracturing technique, showed that between days 12 and 14 the intramembranous particles were aggregated into linear or clustered arrays in the fracture P-face of endothelial cells. This could signify that some kind of gap junction-like coupling may occur between adjacent endothelial cells. Our results also indicate that in advanced stages (21-day-old chick embryos and 14-day-old chicks) the growth of small aggregates into larger aggregates or plaques could occur. In addition to gap junctions, the presence of macular and linear tight junctions, reported as focal tight junctions (day 14 of development) macular and linear tight junctions with free-ending strands oriented parallel to one another (21 days) and smooth contoured ridges (14 days post-hatching) were observed. This sequence of changes may represent a development from linear to macular, to a more occluding arrangement, and may also reflect an endothelial cell polarization. Histochemical study of proteoglycans was done by using cuprolinic blue according to the critical electrolyte concentration method. Cuprolinic blue-positive granular, elongated and microfibrillar materials were found in the subendothelial region, forming a meshwork that occupies the extracellular space. Qualitative and quantitative changes were observed both in proteoglycans and in other extracellular matrix components throughout development, suggesting an increase in extracellular matrix complexity. These results lead us to suggest that the assembly of a more complex extracellular matrix, concomitantly with the formation of intercellular junctions during development, might influence the polarization of endothelium in the aorta of the chick embryo.