Lecture 3: Prenatal Craniofacial Development

At approximately what stage does the head and neck region comprise half of the embryo?

Day 22

What embryonic tissue drives most growth of the facial prominences?

Cranial neural crest–derived mesenchyme

Which brain regions are visible during early face–brain coordination (CS14–CS23)?

Prosencephalon, telencephalon, diencephalon, mesencephalon, rhombencephalon.

What cell population migrates into the pharyngeal arches to drive their expansion?

Cranial neural crest cells (CNCC).

Which craniofacial bones are derived from cranial neural crest cells (CNCC)?

Cranial vault (except parietal), facial bones, mandible.

Which dental cells are derived from cranial neural crest cells (CNCC)?

Odontoblasts (dentin) and pulp fibroblasts.

Which dental cells are not derived from cranial neural crest cells (CNCC)?

Ameloblasts (enamel), which are ectodermal.

Which endocrine cells arise from cranial neural crest cells (CNCC)?

Parafollicular (C) cells of the thyroid

What are the five early facial prominences surrounding the stomodeum?

Frontonasal prominence, paired maxillary processes, paired mandibular processes

Which structure breaks down during the 4th week to open the primitive mouth?

The oropharyngeal membrane

Which pharyngeal arch gives rise to the mandibular processes?

First pharyngeal arch (PA1)

True or false: the maxillary processes arise from PA1

False: they arise as separate swellings rostral to PA1

What induces nasal placode formation?

Ectodermal thickening in the frontonasal prominence.

Nasal placode invagination is similar to the induction of what other structure?

The neural plate

What two processes join during “merging” in midface morphogenesis?

Maxillary process (MXP) and lateral nasal process (LNP).

What process forms the primary palate?

Fusion between the medial nasal process (MNP) and the maxillary process (MXP)/lateral nasal process (LNP)

What structure later forms the secondary palate?

Palatal shelves from the medial maxillary processes

What drives most morphological change in the pharyngeal arches?

Invading cranial neural crest cell (CNCC) mesenchyme

What is the embryological origin of the inner ear?

Otic placode (ectoderm) → otic pit → otic vesicle

What structures form the external and middle ear?

Derivatives of PA1 and PA2, cleft, and pouch.

What ectodermal signaling center patterns the frontonasal region?

The frontonasal ectodermal zone (FEZ) expressing SHH + FGF8.

What happens when frontonasal ectodermal zone (FEZ) tissue is transplanted?

It retains its original SHH/FGF8 pattern and re‑patterns host tissue

What is the role of ectoderm in facial fusion?

It provides signals for epithelial seam breakdown and mesenchymal continuity.

What is the embryological origin of cleft lip?

Failed fusion between medial nasal process (MNP) and MXP/LNP.

The majority of facial growth is driven by _______

Cranial neural crest–derived mesenchyme

The frontonasal, maxillary, and mandibular prominences surround the ________.

Stomodeum

Nasal placodes form by ____ in the frontal nasal prominence (FNP).

ectodermal thickening

Merging of maxillary Maxillary process (MXP) and lateral nasal process (LNP) occurs during the ____ week.

5th

Failure of epithelial seam breakdown leads to _____

cleft lip

______ ossification begins just before palatal development completes.

Palatal shelf

True or False: Maxillary processes arise directly from PA1.

False: they arise as separate swellings rostral to PA1.

True or False: The primary palate forms by fusion.

True— fusion of MNP and MXP/LNP

True or False: The FEZ determines dorsal–ventral facial patterning.

True

True or False: Cleft lip is the third most common birth defect worldwide.

True— 1-700 births

True or False: The inner ear develops from pharyngeal arch mesoderm.

False: it develops from the otic placode (ectoderm).

True or False: External and middle ear malformations often occur with mandibular defects.

True: they share PA1/PA2 origins

What three tissue layers compose each pharyngeal arch?

Ectoderm (outside), endoderm (inside), and mesenchyme (CNCC + mesoderm).

What structures separate pharyngeal arches externally and internally?

Clefts externally and pouches internally

Which cell population fills most of the pharyngeal arch mesenchyme?

Cranial neural crest cells (CNCC)

Which mesodermal population contributes to arch musculature?

Pharyngeal arch mesoderm

Which arch gives rise to the mandibular process?

PA1

Which swelling arises independently of PA1 and appears later?

The maxillary process

What population invades the maxillary process?

Late-migrating CNCC

What induces nasal placode formation?

Ectodermal thickening in the frontonasal prominence

What two processes merge to form the lateral midface?

Maxillary process (MXP) and lateral nasal process (LNP)

What process merges medially to form the lower jaw?

Mandibular process

What type of tissue interaction drives facial outgrowth?

Epithelial–mesenchymal interactions

What structure forms the secondary palate?

Palatal shelves from medial maxillary processes.

What must happen to the tongue for palatal shelves to elevate?

The tongue must lower and move forward

What condition physically blocks palatal shelf elevation?

Macroglossia (enlarged tongue).

What mandibular condition also prevents palatal elevation?

Micrognathia/retrognathia (e.g., Pierre‑Robin sequence).

What is the epithelial seam called at the midline of the secondary palate?

Medial edge epithelium (MEE)

What must happen to the medial edge epithelium (MEE) for fusion to complete?

Breakdown and disappearance of the epithelial seam

What cartilage forms the template for the mandible?

Meckle’s cartilage

Which ear ossicles derive from PA1?

Malleus and incus

Which ear ossicle derives from PA2?

Stapes

What forms the external ear hillocks?

Six hillocks of His from PA1 and PA2.

What developmental defects often co‑occur with external ear malformations?

Mandibular defects, due to shared PA1 origin

Pharyngeal clefts are lined by ______.

ectoderm

Pharyngeal ______ are lined by endoderm.

pouches

The primary palate forms during the _____ week.

6th

Secondary palate formation begins around week _____.

10

Palatal shelves must ____ and _____ above the tongue.

elevate; rotate

The otic placode forms _____ to PA3.

dorsal

True or False: CNCC drive most of the growth of the pharyngeal arches.

True

True or False: Nasal placode invagination is analogous to neural induction.

True

True or False: Pierre‑Robin sequence involves mandibular overgrowth.

False: it involves mandibular UNDERgrowth, elevating the tongue

What two signaling molecules define the frontonasal ectodermal zone (FEZ)?

SHH (ventral) and FGF8 (dorsal).

What is the functional role of the frontonasal ectodermal zone (FEZ)?

It directs dorsal–ventral patterning and outgrowth of the frontonasal prominence

Which tissue expresses SHH/FGF8 first — neural tissue or ectoderm?

Neural tissue

What happens when FEZ tissue is rotated 180°?

It repatterns the host face according to the donor’s DV identity.

What is the relationship between CNCC and ectoderm in facial development?

They engage in reciprocal signaling that shapes facial form.

What role does ectoderm play in facial outgrowth?

It guides lineage decisions of underlying CNCC.

What gene is associated with Treacher‑Collins syndrome?

TCOF1

What gene is associated with CHARGE syndrome?

CHD7

Neural expression of ____ precedes ectodermal expression.

SHH/FGF8

FEZ grafts show that ____ retains its intrinsic patterning.

ectoderm

True or False: The FEZ is defined by BMP and WNT signaling.

False: it is defined by SHH (ventral) and FGF8 (dorsal).

True or False: Cleft lip and cleft primary palate share the same embryological origin.

True— both involve MNP-MXP/LNP fusion failure

What adult structures arise from Meckel’s cartilage?

Malleus, incus, and sphenomandibular ligament