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In vitro development of the hamster and chick secondary palate
Insights
Mammalian palatal shelf fusion involves medial edge epithelium (MEE) differentiation, characterized by decreased DNA synthesis and increased cAMP, leading to cell death. Avian palatal shelves, which do not fuse, maintain MEE integrity via sustained DNA synthesis and low cAMP levels.
Area of Science:
- Developmental Biology
- Cell Biology
- Tissue Engineering
Background:
- Palatogenesis, the process of palate formation, involves the fusion of palatal shelves.
- The medial edge epithelium (MEE) plays a critical role in this fusion process.
- Differences in palatal fusion between mammals (fuse) and birds (do not fuse) offer a model to study MEE behavior.
Purpose of the Study:
- To compare the in vitro behavior of medial edge epithelium (MEE) in hamster (fusing) and chick (non-fusing) embryos during palatogenesis.
- To investigate the factors influencing MEE differentiation and cell death in mammalian palatal shelves.
- To determine the role of cell contact and signaling molecules like cAMP in MEE fate.
Main Methods:
- In vitro culture of homotypic (hamster-hamster, chick-chick) and heterotypic (hamster-chick) palatal shelves.
- Assessment of MEE differentiation markers: DNA synthesis, cyclic adenosine monophosphate (cAMP) levels, and cell death (cytolysis).
- Microscopic examination of epithelial-mesenchymal interactions and cell fate.
Main Results:
- Mammalian MEE differentiation in vitro involves cessation of DNA synthesis, elevated cAMP, and cell death, independent of direct cell contact.
- Chick MEE, cultured under identical conditions, did not exhibit these pre-fusion characteristics.
- Heterotypic contact induced cytolysis in chick MEE, potentially mediated by lysosomal enzymes from hamster MEE or hamster mesenchymal signals.
Conclusions:
- Mammalian palatal shelf fusion is associated with MEE elimination driven by increased cAMP levels and suppressed DNA synthesis.
- Avian palatal shelves maintain MEE integrity through sustained DNA synthesis and low cAMP levels, preventing fusion.
- Lysosomal enzyme release from differentiating hamster MEE may be crucial for mesenchymal continuity during mammalian palatogenesis.
Abstract:
A series of experiments were undertaken to compare the in vitro behaviour of the medial edge epithelium (MEE) of hamster, in which palatal shelves normally fuse, and chick, in which they do not fuse. Homotypic pairs of hamster and chick embryo palatal processes, single palatal processes, and heterotypic palatal shelves of both animals were grown in vitro. The results indicated that contact between palatal shelves may not be crucial for MEE differentiation in mammals. The ability to acquire pre-fusion characteristics may be present in mammalian palatal tissue from their early development and may be expressed by cessation of DNA synthesis in the MEE, elevation of cAMP, and MEE cell death. Isolated chick palatal shelf cultured under identical conditions did not express these mammalian pre-fusion characteristics. When MEE of hamster and chick palatal shelves were placed in contact with one another, the intervening epithelia underwent cytolysis. This could be due to either the destruction of chick MEE by lysosomal enzymes liberated from adjacent degenerating hamster MEE cells, or by induction of cell death in chick MEE by hamster mesenchyme. Heterotypic palatal tissue combinations also suggest that release of lysosomal enzymes in the hamster MEE, which leads to its dissolution, may be the terminal event in epithelial differentiation prior to the establishment of mesenchymal continuity. It is suggested that an inverse relationship exists between DNA synthesis and cAMP levels during palatogenesis: when palate closes (as in mammals) the MEE is eliminated by increasing cAMP levels, whereas when palate remains open (as in birds) low level of cAMP preserve the integrity of MEE by supporting DNA synthesis.