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The head-process and the formation of the definitive endoderm in the mouse embryo
Abstract:
The formation of the secondary or definitive endoderm was studied by light microscopy (1-mu m sections) and (scanning) electron microscopy. The results show that the primary endoderm disappears axially, and a hiatus appears in this layer. The development of this hiatus may be caused by cell degeneration, which is observed in the primary endoderm, or by some activity of the underlying head-process. The apical parts of a number of head-process cells converge towards a hiatus. These cells are organized into a conical configuration which may participate in the formation of the hiatus. The cone cells reach through the hiatus into the yolk sac cavity, and comprise the secondary endoderm. The consequence is that in mice, the definitive endoderm develops from the head-process mesoderm rather than from the primary endoderm.
Insights
The definitive endoderm in mice originates from head-process mesoderm, not primary endoderm. This occurs as the primary endoderm axially disappears, forming a hiatus that the head-process cells then fill.
Area of Science:
- Developmental biology
- Embryology
- Cell biology
Background:
- The formation of the definitive endoderm is a critical early developmental event.
- Previous understanding suggested the definitive endoderm arises from the primary endoderm.
Purpose of the Study:
- To investigate the cellular mechanisms underlying secondary or definitive endoderm formation in mice.
- To clarify the origin of the definitive endoderm.
Main Methods:
- Light microscopy (1-µm sections) for detailed tissue observation.
- Scanning electron microscopy for high-resolution surface imaging.
Main Results:
- The primary endoderm was observed to disappear axially, creating a hiatus.
- Head-process cells, organized in a conical shape, converged towards and penetrated this hiatus.
- These cells formed the secondary endoderm within the yolk sac cavity.
Conclusions:
- In mice, the definitive endoderm originates from the head-process mesoderm.
- The primary endoderm does not directly contribute to the definitive endoderm in this model.