Molecular Odontogenesis Flashcards
Where and when are cranial neural crest cells formed?
at the back of the neural tube on approximately E22 (week 3)
When do the neural crest cells begin to migrate?
when the neural tube closes toward the branchial arches
T/F. Neural crest cells are considered to be stem cells.
True.
What is the name for ridges formed on the sides of the head and neck at embryo week 4?
branchial (pharyngeal) arches
The face is represented by the ___ process and the ___ branchial arch (maxillary and mandubular processes).
frontonasal; first
Where are teeth developed?
in the first branchial arch
A single stem cell can ___ itself and become involved in self-renewal. Or, it can ___ into varied types of mature cells.
replicate; differentiate
T/F. Self-renewing stem cells can undergo symmetric or asymmetric division.
True.
Neural crest cells become ectomesenchymal cells when ___ and ___ interact. They can later develop into odontoblasts or cementoblasts.
endodem; ectoderm
Neural crest cells of the first branchial arch arise from which hindbrain rhmobomere?
r1 and r2
What are the three migratory streams of hindbrain-derived neural crest cells?
- 1st branchial arch = r 1-2
- 2nd branchial arch = r4
- 3rd branchial arch = r 6-7
Which rhmobomeres dies after serving as separators between the remaining rhmobomeres?
r3 and r5
Meanwhile, the branchiomotor nerves collect axons from cell bodies but exit the hindbrain only from the ___ numbered segemnts to innervate their peripheral target structures.
even
Matching:
A. Trigeminal nerve (V)
B. Facial nerve (VII)
C. Glosopharyngeal nerve (IX)
- r1-3
- r4-5
- r6-7
A-1
B-2
C-3
NCCs in each migratory stream express specific ___ gene codes.
Hox
T/F. Hox genes are a group of homeobox genes, which posses a unique homeobox (DNA sequence), which encodes a conservative homeodomain (protein segment).
True.
If a Hox gene is expressed, its protein product functions as a ___ ___ which controls other gene expressions.
transcription factor
T/F. NCCs that migrate to the 1st branchial arches start expressing Hox gene but it stops once it reaches the 2nd branchial arch (even though they carry the gene).
False, NCCs that migrate to the 1st branchial arch are HOX FREE, but they carry the genes and don’t express them. NCCs that migrate to the 2nd branchial arch start expressing Hox gene (r4).
NCCs involved in ___ development do NOT express Hox genes.
tooth
What gene accounts for the difference between the maxilla and mandible?
Dlx gene
___ 1/2 combination is required for development of the proximal portion of the ___ branchial arch (___ process).
Dlx; first; maxillary
Which Dlx gene is required for the development of the distal portion of the 1st branchial arch (mandibular process)?
Dlx 5/6
Epithelium is derived from ___ and develop into ___ that make enamel during the late bell stage. This epithelium interacts with mesenchyme derived from ___ and ___ that become odontoblasts and form ___.
ectoderm; ameloblast; NCCs; mesoderm; dentin
T/F. All tooth structures are directly contributed by cranial neural crest cells that migrated to the 1st branchial arch.
False, all tooth structures (dentin, cementum, pulp, periodontal ligament) EXCEPT enamel.
What four molecules bind to cell membrane receptors and impact gene regulation through varied intracellular pathways of ectoderm-derived epithelium?
BMP, FGF, Wnt, SHH
T/F. BMP, FGF, Wnt, SHH are only involve din the development of ectodermally-derived tooth structures.
False, they are also important for the development of other ectodermal organs, such as hair, nails, and glands
What are epithelial aggregates that function as signal centers for tooth morphogenesis and odontoblast differentiation?
enamel knots
What structure appears at the end of the bud stage and is essential for bud-to-cap stage transition?
Primary enamel knots, without it, tooth development would be arrested
What structure appears at the location of future molar cusps at the bell stage and determine the number and location of the molar cusp?
secondary enamel knots
Are secondary enamel knots found in incisors?
no
___ may function as a ___ ___, while BMPs may function as an ___ to regulate the formation of inter-cusp distance.
FGF; cusp activator; inhibitor
What are the three major stages that the development of a tooth crown can be divided into?
- initiation
- morphogenesis
- differentiation and mineralization
How is molar tooth identity determined differently from inciors?
different molecular interactions are present at the anterior (BMP/Msx1/2) and posterior (FGF/Dlx2) regions, which may control the development of incisors and molars, respectively.
When do pioneer trigeminal nerve axons penetrate into the dental pulp?
after the start of enamel formation (late bell stage)
Epithelium expressing ___ communicate with mesenchyme and serve as a chemorepellent for axons controlling the timing and patterning of tooth innervation.
Sema 3A
After the crown development is nearly complete, HERS grows apically between two mesenchymal regions. Name them.
dental papilla and dental follicle
After HERS formation, apical ___ appear adjacent to the HERS on the ___ side.
odontoblasts; papilla
T/F. Although enamel is not present in the final root, induction from the epithelium is required for root development.
True.
What does HERS induce dental papilla cells to differentiate into?
apical odontoblasts, their differentiation may be through lamini-5 and TGF-beta secreted by HERS
Are odonotoblast in the crown or root region much less elongated?
root
___ ___ ___ is essential for root dentin formation but not for crown dentin formation. Without this, odonotoblast cannot normally form even when the ___ appear normal.
Nuclear factor 1c; HERS
When does cementum formation start?
when HERS (epithelial) and dental follicle (mesenchymal) are in close proximity
T/F. Most molecules involved in crown development are different from root development.
True.
What are the fates of HERS?
become epithelial rest of Malassez apoptosis incorporated into the cementum front epithelial-mesenchymal transformation migration to the periodontal ligament differentiation into cementoblasts
T/F. Ectodermal displasia syndrome affects one ectodrrmal structure, teeth.
False, two or more ectodermal structures (hair, nails) are affected.
In ectodermal dysplasia, mutations of transcription factor ___ disrupt normal signailing of FGF, BMP, and SHH.
p63
Affected family members missing max and mand 2nd premolars have a mutation in the homeodomain region, which affects the normal function of ___ protein as a ___ ___.
Msx1; transcription factor
People missing premolars have a ___-___ transversion (arginine-proline) mutation of the Msx1 gene.
G-C
What is mutated in individuals who have no molar development?
Pax9 is mutated. There is a guanine insertion causing a reading frameshift of the gene.
The Pax9 mutation is at its ___-___ ___, which affects the normal functionof Pax9 protein as a ___ ___.
DNA-binding domain; transcription factor
T/F. Individuals with an Axin2 mutation have more than 7 permanant teeth undeveloped.
False, its more than 8.
T/F. Affected members either have a missense (C-T) or insertion (G) mutation. Both mutations introduce a premature stop codon to the Axin2 gene.
True.
During tooth development, Axin2 is expressed intensively in the ___. Loss of Axin2 function disrupts the ___ signaling, but Axin2 does not function as a ___ ___.
Mesenchyme; Wnt; transcription factor
Which mutation haspatients who are prone to colorectal polyps and cancer?
Axin2
A patient presents with mulitple missing anterior teeth. You discover that the cause is due to a missense mutation. What gene is mutated and what happens to the product of this gene?
EDA gene. The product is a transmembrane signaling molecule belonging to the TNF pathway.
Does the the product of the EDA gene function as a transcription factor?
No.
What are some theories for the etiology of supernumerary teeth?
atavism (evoluntionary throwback)
tooth germ dichotomy (like in a cleft region)
hyperactivity of the dental lamina
genetic and environmental factors
T/F. Most supernumerary teeth are isolated cases. Multiple supernumerary teeth are relatively rare, but can happen in certain systemic conditions.
True.
Cleidocranial dysplasia is an autosomal ___ skeletal dysplasia in the ___ or sutures. It is caused by a mutation in ___ that encodes for a ___ ___. This gene is a positive regulator for primary, not secondary teeth.
dominant; clavicle; Runx2; transcription factor
Whaat is the cause of Gardner’s syndrome?
APC gene mutation
What is APC deficiency mediated by?
Beta-catenin (Wnt pathway)
