Facial and palatal development

L.Moss-Salentijn

Contributions to the external face

Periprosencephalon: ectoderm and mostly nc-derived mesenchyme surrounding the forebrain. Frontonasal process.

First pharyngeal (mandibular) arch. Mandibular and maxillary processes.

Slide 5

Oropharyngeal membrane (buccopharyngeal, oral)

Disintegration of oropharyngeal membrane

Stomodeum at 4 weeks

Facial processes (prominences)

Connexin (gap junctions!) expression in the facial processes at different stages of chick face development. These are the cell groups that contribute most to the overall expansion of the facial processes.

Development external face (4-5 wks)

Development external face (6-8 wks)

Face development - animation

Dimensional changes (4-6 wks)

10-fold linear increase in size !

Merging

Differential mesenchymal proliferation.
Elimination of groove.

Merging with epithelial inclusion

Sites of potential facial clefts

Fusion

Contact and fusion of epithelium-covered surfaces. Removal of epithelium

Fusion in primary and secondary palate development

Fate of fused epithelium

Non-proliferating epithelium in rapidly growing environment: passive stretch and incorporation in nearby surface epithelia

Apoptosis and phagocytosis

Epithelial-mesenchymal transformation (?)

Development of nose

Slide 23

Slide 24

Slide 25

Oronasal membrane

Primary (primitive) palate

Development of primary and secondary palate

Intrinsic factors in the successful development of the secondary palate: increase in size of palatal processes

Mesenchymal cell proliferation – ceases hours before palatal processes become horizontal

ECM production increasing volume of palatal processes

Hydration of ECM – major increase in volume and turgor just prior to horizontalization

Secondary palate development

Slide 31

Horizontalization of palatal processes

Factors contributing to the horizontalization of the palatal processes

Turgor in the palatal processes

Movements of the tongue – primitive swallowing- allowing tongue to move out of the way

Downward and forward growth of lower jaw complex – providing space for the secondary palate

Straightening of the cranial base – providing mechanical conditions for horizontalization

Slide 34

Slide 35

Factors contributing to the successful fusion of the secondary palate: the medial edge epithelium (MEE)

Apoptosis of MEE surface cells immediately prior to fusion

Development of temporary glycoprotein membrane coating, enabling adhesion between MEE cells of opposing palatal processes

Successful removal of MEE from fusion line

Slide 37

Slide 38

Completion of palate formation

Sites of potential palatal clefts


	Periprosencephalon: ectoderm and mostly nc-derived mesenchyme surrounding the forebrain. Frontonasal process.
	First pharyngeal (mandibular) arch. Mandibular and maxillary processes.


	Non-proliferating epithelium in rapidly growing environment: passive stretch and incorporation in nearby surface epithelia
	Apoptosis and phagocytosis
	Epithelial-mesenchymal transformation (?)


	Mesenchymal cell proliferation – ceases hours before palatal processes become horizontal
	ECM production increasing volume of palatal processes
	Hydration of ECM – major increase in volume and turgor just prior to horizontalization


	Turgor in the palatal processes
	Movements of the tongue – primitive swallowing- allowing tongue to move out of the way
	Downward and forward growth of lower jaw complex – providing space for the secondary palate
	Straightening of the cranial base – providing mechanical conditions for horizontalization


	Apoptosis of MEE surface cells immediately prior to fusion
	Development of temporary glycoprotein membrane coating, enabling adhesion between MEE cells of opposing palatal processes
	Successful removal of MEE from fusion line