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Developmental mechanisms in normal and abnormal palate formation with particular reference to the aetiology,
Insights
Palatal shelf reorientation in rats involves mucopolysaccharide hydration, while alligators exhibit horizontal shelf growth. This comparative study reveals insights into mammalian secondary palate development and cleft palate formation.
Area of Science:
- Developmental Biology
- Comparative Anatomy
- Teratology
Background:
- Palatal development is crucial for separating oral and nasal cavities.
- Mammalian secondary palates form through shelf elevation, a process not fully understood.
- Cleft palate is a common congenital anomaly with significant morbidity.
Purpose of the Study:
- To investigate the mechanisms of palatal shelf elevation in rats.
- To compare palatal development in rats with the unique secondary palate formation in alligators.
- To explore the role of mucopolysaccharides in palatal development and cleft palate induction.
Main Methods:
- Macroscopic, microscopic, and ultrastructural examination of rat and alligator foetuses.
- Induction of cleft palate in rat foetuses using 5-fluoro-2-desoxyuridine.
- Analysis of mesenchymal mucopolysaccharide synthesis during palatal development.
Main Results:
- Rat palatal shelves elevate rapidly, driven by mucopolysaccharide hydration.
- Cleft palate induction in rats significantly reduced mucopolysaccharide synthesis.
- Alligator palatal shelves exhibit de novo horizontal growth, facilitated by a small tongue.
Conclusions:
- Mucopolysaccharides, particularly hyaluronic acid, play a key role in mammalian palatal shelf elevation.
- The alligator serves as a valuable model for studying secondary palate formation due to its unique developmental strategy.
- Tongue size and oronasal cavity space are critical factors influencing palatal shelf orientation during development.
Abstract:
Palatal development was studied macroscopically, microscopically and ultrastructurally in foetuses of inbred Wistar rats and Alligator mississippiensis. In the rat, elevation of the palatal shelves from a vertical position lateral to the tongue to a horizontal position above the tongue, occurs very rapidly. This reorientation is postulated to be caused by an intrinsic turgor shelf force generated by the hydration of mesenchymal mucopolysaccharides (predominantly hyaluronic acid). Cleft palate was induced in rat foetuses using 5-fluoro-2-desoxyuridine and was associated with greatly decreased mucopolysaccharide synthesis. The alligator is the only animal which develops in an external egg and which possesses a true mammal-like secondary palate: it is therefore a useful animal model system because longitudinal studies and direct surgical and pharmacological manipulations can be performed. The palatal shelves of alligators grow horizontally above the dorsum of the tongue from their first appearance. This de novo horizontal shelf growth is associated with an increase amount of space in the alligator oronasal cavity due to the small, fatty, alligator tongue. It is postulated that the evolution of the large muscular mammalian tongue constrains the palatal shelves to grow vertically until sufficient space can be created to form the common nasal passage simultaneous with shelf elevation.