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Chondroid tissue in the early facial morphogenesis of the chick embryo
B Lengelé1, J Schowing, A Dhem
1Human Anatomy Research Unit, Faculty of Medicine, University of Louvain, Brussels, Belgium.
Insights
Chick embryo facial bones initially develop from chondroid tissue, not direct intramembranous ossification. This study reveals chondroid tissue as the first skeletogenic differentiation in facial bone development.
Area of Science:
- Developmental biology
- Histology
- Embryology
Background:
- Facial skeleton development is crucial for vertebrate evolution.
- Intramembranous ossification is the traditionally accepted mechanism for facial bone formation.
- Early skeletal differentiation in avian embryos requires further investigation.
Purpose of the Study:
- To investigate the initial calcified tissue formation during early facial skeleton morphogenesis in chick embryos.
- To clarify the role of chondroid tissue in the development of intramembranous facial bones.
- To compare facial bone development with cranial vault ossification.
Main Methods:
- Microradiographic techniques were employed to visualize calcified tissues.
- Histological analysis provided detailed structural information.
- Study conducted on 22 chick embryos at critical developmental stages (9th, 12th, and 14th incubation days).
Main Results:
- On day 9, facial bones and palatal vault consist of chondroid tissue within mesenchymal condensations.
- Woven and lamellar bone formation initiate by day 12, primarily on the external side of chondroid precursors.
- Similar developmental patterns observed in both upper and lower facial/mandibular bones.
Conclusions:
- The primitive facial desmocranium in chick embryos initially comprises chondroid tissue.
- This finding challenges the classical view of purely intramembranous ossification for facial bone development.
- Chondroid tissue represents the initial mode of skeletogenic differentiation in avian facial mesenchyme, akin to cranial vault development.
Abstract:
The calcified tissues involved in the early morphogenesis of the so-called intramembranous bones of the facial skeleton were studied by microradiographic and histological techniques in 22 chick embryos at the 9th, 12th and 14th days of incubation. On the 9th day, the bones of the upper face and palatal vault are made up of thin sheets of chondroid tissue, deposited in their respective mesenchymal condensations. Woven and lamellar bone formation subsequently takes place in each of them from the 12th day of incubation, mainly on the external side of their chondroid primordia. The same phenomena occur in the lower facial and mandibular bones. These facts indicate that the primitive facial desmocranium of the chick embryo, which is classically considered to be formed by intramembranous ossification, first consists of chondroid tissue. As in the cranial vault, this tissue thus represents the initial modality of the skeletogenic differentiation within the avian facial mesenchyme.