Lecture 1 Flashcards by Ashley Haghighi

DLX3
regulates?

mutations lead to?

hair follicle differentiation
Enamel genes
Bone formation, resorption, and homeostasis

leads to trichodentoosseus syndrome

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At what days:
morulla
Blastocyst
implantation into uterine wall

3-4 days morulla

5 days blastocyst

implants into uterine wall at day 14

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Blastocyst stage description

Comprises of trophoblast and embryoblast/ICM.

Inner cell mass becomes all tissues of embryo

First differentiation of cells

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Blastocyst at 13 days (end of week 2)

Formation of two germ layers
-ectoderm and endoderm

Thickening of prechordal plate between the two germ layers

Bilaminar 2 layer embryo

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Gastrulation
occurs when?
How does it happen?

occurs at the end of the 3rd week

Primitive node is formed then primitive streak. Ectodermal cells migrate through primitive streak to form new population of cells between ecto and endoderm.

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What forms the notocord

cephalic, more rostral migrating cells form the notocord to support the embryo

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What comprises buccopharyngeal membrane

remains bilayer of ectoderm and endoderm with no intervening mesoderm

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What key things happen during weeks 4 - 8

Differentiation
Major structures
Rapid change

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Rostro-caudal (front back) folding occurs during

result of this folding results in?

week 4
-Cardiac plate moves inwards as it develops below buccopharyngeal membrane

-formation of a mouth/stomatodeum, stomodeum is the primitive oral cavity

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Neural crest cells

How does ectoderm form outer surface of the embryo

when is all this happening

what happens to endoderm

come together to form the neural tube.

edges of ecto derm push up and crow around the endoderm. Pushing down and forming circle around endo and meso and forms outer surface of the embryo
week 4
endoderm starts as a flat surface and gets pinched off as ectoderm forms around it-> forms the gut

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Buccopharyngeal membrane forms:

back of mouth and front of primitive gut

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Stomatodeum is at first bounded by

superior: frontal prominence
inferior: Cardiac bulge
posterior: Buccopharyngeal membrane

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Stomatodeum, branchial arches, cardiac bulge, buccopharyngeal membrane

as branchial arches develop, cardiac bulge is displaced by them.

posterior border of stomatodeum becomes branchial arch 1
buccopharyngeal membrane ruptures and allows communication between mouth and foregut

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Cranial neural crest cells
derived from what germ layer?
adjacent to? separates from what when?
has the capacity to do what?

Derived from ectoderm

adjacent to the neural tube
separates from neural plate when neural tube closes
capacity to migrate and differentiate extensively

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Cranial neural crest cells undergo:
referred to as:
forms what

epithelial to mesenchymal transformation

ectomesenchymal cells
most of the connective tissues of the head including teeth and their supportive tissues
also migrate to branchial arch 1

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Some craniofacial bones come from

ectomesenchyme derived from neural crest cells

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Skeletal bones come from

mesoderm

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neural tube expands as

forebrain midbrain and hindbrain

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hindbrain forms

8 rhombomeres/bulges

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what parts of the neural tube form branchial arch 1

The midbrain and rhombomeres 1 and 2

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Pattern of NCC migration
First stream forms:
second stream forms:

the face

branchial arch 1

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Neural crest cells from rhombomeres> or equal to 3 express

Hox transcription facors/genes

do craniofacial regions use hox genes? why?

craniofacial region is a more recent evolutionary structure, developed new sets of TFs

Hox TFs
Homeobox TFs
All transcription factors have

very ancient genes involved in ancient body pattern direction
*subset of homeobox
includes a specific 180 base pair homeobox with specific sequence
include DNA binding domain that allows them to interact with and regulate genes

Branchial arches form by

Infiltrating Neural crest cells and proliferating mesoderm

Each arch is comprised of

``` external bump (ectoderm) Internal bump (endoderm) -within internal bump is a mix of neural crest cells and mesoderm ```

Grooves/clefts

separate arches externally (ectoderm)

Pouches

Internal depression (endoderm)

Branchial arches and clefts appear and disappear quickly within

4th week

Branchial arch 1 becomes pouch and groove Cleft I forms

right and left maxillary facial processes and right and left mandibular facial processes - becomes outer and middle ear - external auditory meatus

where maxillary and mandibular processes meet

commissura labiorum oris

Branchial arch II forms

operculum that folds over BAIII and IV and clefts II, III, IV

Dlx homeobox TFs mutation?

causes altered craniofacial morphology | -lack of maxillary molars

Treacher-collins syndrome caused by

underdevelopment of craniofacial region and mandible | -failure/impairment of NCC migration to facial region

Process of merging is what

Elimination of furrows between already connected tissues | -mandibular processes grow together medially. Proliferation of mesenchyme to fill in furrows

Fusion: what structures utilize this

breakdown of surface epithelium to unify previously separate processes - palatine shelves come together and merge - maxillary processes come together medially - medial nasal processes and maxillary prcesses unify

Formation of the face from weeks 4-6 what occurs?

Boundaries of stomatodeum on day 26 is from branchial arch I from the right and left maxillary and mandibular processes Odontogenic epithelium present as maxillary and mandibular processes merge Nasal placodes begin forming (proliferation)

2 nasal pits form within

frontal prominence

medial nasal processes forms:

philtrum of upper lip | Midline of nose

Frontal prominence becomes

medial nasal processes | Lateral nasal processes

Lateral nasal processes form

lateral sides of nose, ala of nose, infraorbital area

Maxillary processes become

upper parts of cheeks | lateral parts of upper lip

mandibular processes become

lower parts of cheeks - lower lip - chin

Tongue appears during | -originates from?

fourth week -four lingual swellings on internal surfaces of branchial arches I, II, III (mainly I and III) Tuberculum impar forms at midline of branchial arch I mandibular process - Lingual swellings (from BAI) on either side of tuberculum impar - Copula (BAII) is overgrown by large hypobranchial eminence (BAIII)

What forms anterior 2/3 of the tongue

lateral lingual swellings merge with each other and with tuberculum impar

What forms posterior 1/3 of tongue (root)

When hypobranchial eminence from BA III overgrows copula

what forms epiglottis

posterior BA IV

What forms mucosa of anterior 2/3 -Innervation? What forms mucosa of posterior 1/3 -Innervation? Muscle -Innervation?

Branchial arch I -Cranial nerve 5 (Trigeminal) Branchial arch III Glossopharyngeal (CNIX) Occipital somites Hypoglossal (XII)

Oral cavity at ____ weeks has a ______ but no _____

5 weeks has a stomatodeum but no separation of oral and nasal cavities

Structures within the stomatodeum include

``` primary palate (from median nasal processes of frontal prominence) Nasal septum (from primary palate) palatine shelves/folds (from maxillary facial processes) ```

secondary palate formation stages - 7 weeks - 7-8 weeks - 9+ weeks

1. Palatine shelves facing downwards (vertical) 2. Tongue depressed, palatine shelves elevated but not fused 3. Fusion of shelves and nasal septum to form secondary palate

Fusion of primary palate, nasal palate, and palatine shelves/folds occurs via

anterior to posterior direction

Defects in first 4 weeks vs 4-8 weeks Most common birth defects?

4-> often lethal 4-8-> more likely to form malformations Cleft lip and palate

Interferon regulatory factor 6

Transcription factor expressed in oral epithelium during face formation palatogenesis and tooth formation -mutations associated with orofacial clefting