Genetics in tooth development

GENETICS IN
TOOTH
DEVELOPMENT
Dr Akhil S
Department of Oral Pathology
Malabar Dental college & Research
centre
Edappal

 INTRODUCTION
 STAGES OF TOOTH DEVELOPMENT
 MOLECULAR CONTROL OF TOOTH
DEVELOPMENT
 CONCLUSION
 REFERENCES

INTRODUCTION:
•The primitive oral cavity, or stomodeum, is lined by
stratified squamous epithelium called the oral ectoderm
• The oral ectoderm contacts the endoderm of the foregut
to form the buccopharyngeal membrane

• Membrane ruptures at about 27th day of gestation
and the primitive oral cavity establishes a
connection with the foregut
• Most of the connective tissue cells underlying
the oral ectoderm are of neural crest or
ectomesenchyme in origin
•These cells instruct the overlying ectoderm to
start the tooth development, which begins in the
anterior portion of the future maxilla & mandible
and proceeds posteriorly

Initiation of Tooth Development
The initiation of tooth development begins at 37 days of develop
with formation of a continuous horseshoe-band of thickened epit
in the location of upper and lower jaws – Primary Epithelial Band
Each band of epithelium will give
rise to 2 sub divisions:
1. Dental lamina and
2. Vestibular lamina
Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 8thedition

Dental
Lamina
• Dental lamina appears as a
thickening
of the oral epithelium adjacent to
condensation of ectomesenchyme
• 20 areas of enlargement or knobs
Primary epithelial
band
Ectomesenchyme
Figures from: http://www.usc.edu/hsc/dental/ohisto/

1. Bud Stage
• Bud stage is characterized by rounded, localized growth
of
epithelium surrounded by proliferating mesenchymal
cells,
which are packed closely beneath and around the
epithelial buds
http://www.usc.edu/hsc/dental/ohisto/

1. Bud Stage
In the bud stage, the enamel organ consists of peripherally
located
low columnar cells and centrally located polygonal cells

2. Cap Stage
Enamel Organ Dental Papilla

2. Cap Stage
Enamel organ
Dental papilla
Dental follicle or sac
Dental follicle or dental sac is the condensed ectomesenchymal tissue
surrounding the enamel organ and dental papilla. This gives rise to
cementum and the periodontal ligament (support structures for tooth)
Enamel knot

Enamel Knot: Densely packed accumulation of cells projecting from the
inner
enamel epithelium into dental papilla.

3. Bell Stage
• Continued growth leads to bell stage, where the enamel organ resembles a
bell with deepening of the epithelium over the dental papilla
• Continuation of histodifferentiation (ameloblasts and odontoblasts are defined)
and beginning of morphodifferentiation (tooth crown assumes its final shape)
Dental lamina
Outer
dental
epithelium
Inner
dental
epitheliumDental papilla
Dental follicle
Cervical loop

3. Bell Stage (Early)
Inner dental epithelium: Short columnar cells bordering the dental papilla.
These will eventually become ameloblasts. The cells of inner dental
epithelium exert an organizing influence on the underlying mesenchymal cells
in the dental papilla, which later differentiate into odontoblasts
Outer dental epithelium: Cuboidal cells which bring nutrition to the ameloblasts.
Stellate reticulum
Inner dental epithelium
Stratum intermedium
Dental papilla
Outer dental epithelium

3. Bell Stage (Early)
Stellate reticulum
Stratum intermedium
Dental papilla
Stellate reticulum: Star-shaped cells with process.
These cells secrete glycosaminoglycans & support and protect the delicate
enamel organ.
Stratum intermedium: Cell layer between the inner dental epithelium and
stellate reticulum which have high alkaline phosphatase activity. They assist
inner dental epithelium (ameloblasts) to form enamel.

Cervical loop
Cervical loop: Area where the inner and the outer dental epithelium meet at
the rim of the enamel organ. This point is where the cells will continue to
divide until the tooth crown attains its full size and which after crown
formation will give rise to the epithelium for root formation. (Zone of reflection)
3. Bell Stage
http://www.usc.edu/hsc/dental/ohisto

Future crown patterning also occurs in the bell stage, by folding of the
inner dental epithelium. Cessation of mitotic activity within the inner
dental epithelium determines the shape of a tooth.
Crown Pattern Determination

Hard Tissue Formation
Deposition of dental hard tissues is
called “apposition”
After the crown attains its final
shape during cap to early bell stage,
the inner dental epithelial cells stop
to proliferate, except the cells at the
cervical loop
The boundary between the
odontoblasts
and inner dental epithelium defines the
future dentino-enamel junction

Apposition
 When the inner
dental epithelium is differentiating,
the undifferentiated ectomesenchymal
cells increase rapidly in size and
ultimately differentiate into odontoblasts
 Differentiation of odontoblasts from
ectomesenchymal cells are induced by
influence from the inner dental epithelium
Odontoblasts Dentin
Enamel
Ameloblasts

Root Formation
Development of root begins after the enamel and dentin formation has
reached the future cementoenamel junction
Epithelial cells of the inner and outer dental epithelium proliferate from the
cervical loop of the enamel organ to form the Hertwig’s epithelial root sheath.
The root sheath determines if a tooth has single or multiple roots, is short or
long, or is curved or straight.
Hertwig’s epithelial
root sheath

Primary apical formen
Epithelial diaphragm: the proliferating
end of the root sheath bends at a near
45-degree angle. The epithelial
diaphragm will encircle the apical
opening of the dental pulp during root
development

Hertwig’s epithelial
root sheath
Stratum intermedium
Eventually the root sheath will fragment to form several discrete clusters
of epithelial cells known as epithelial cell rests of malassez. These will persist in
adults within the periodontal ligament

The epithelial rests appear as small clusters of epithelial cells which are
located in the periodontal ligament adjacent to the surface of cementum.
They are cellular residues of the embryonic structure known as Hertwig's
epithelial root sheath.
Epithelial Cell Rests of Malassez
http://www.usc.edu/hsc/dental/ohisto

Secondary apical foramen form as a result of two or three tongues of
epithelium growing inward toward each other resulting in multirooted teeth
Essentials of Oral Histology and Embryology,
Ed: James Avery, 2nd edition. 2000

Tooth development features a sophisticated series of signaling interactions
between the oral epithelium and the underlying mesenchyme

Fgf - Fibroblast growth factor
Msx - Muscle specific homeobox like gene
BMP - Bone morphogenic protein
Pax - Paired boxhomeotic gene
Lef - Lymphoid enhancer factor
Shh - Sonic hedgehog
Dlx - Distal-less gene homologue
Gli - Glioma associated oncogene
Lhx - LIM homeobox genes

Gene responsible for tooth formation comprised of
 Transcription factors
 Growth factor
 Receptor

Lhx
 Lim- homeobox domain genes
 Expressed as transcription factors
 Controls the pattern of tooth formation

Pax
 Member of Pax gene family
 Defines the localization of tooth germs
 Encodes a paired domain containing transcription factor

Lef-1
 Lymphoid enhancer factor
 First expressed in the dental epithelium.Then shifts to
mesenchyme during the bud stage.
 Its mutation shows arrest of all dental development in
bud stage.

MSX 1
 Initially called homeobox 7
 A nonclustered homeobox protein
 Member of the muscle segment homeobox gene family
 First gene to be definitively associated with human
tooth agenesis.
Pani SC. The genetic basis of tooth agenesis: Basic concepts and genes
involved. J Indian Soc Pedod Prev Dent 2011;29:84-9.

LTBP3
 Latent transforming growth factor beta binding protein 3
 Gene that modulates the bioavailability of TGF-β.
Pani SC. The genetic basis of tooth agenesis: Basic concepts and genes involved. J
Indian Soc Pedod Prev Dent 2011;29:84-9.

 Oral epithelium sends signals to underlying mesenchyme.
 Under the influence of these signals the mesenchyme starts responding by
expressing various regulatory genes.

Oral Ectoderm and Tooth
Patterning
Recombination experiments show that
at early (E10.5) time point the epithelium
directs patterning, however at later time
(E11.0) mesenchyme directs patterning –
Reciprocal Signaling

Oral- aboral axis formation
Fgf 8 – expressed by oral epithelium- causes FGF production. (E 9)
production of Lhx 6 and Lhx 7- on ectomesenchyme
 Control pattern of tooth formation.
 Action of Fgf and Lhx controls the oral-aboral axis.

Genetics in dentistry by G P Pal

Enamel knot:
 Transient clusters of epithelial cells
 Transient signaling center of epithelium.
 Responsible for the tooth cusps formation.
 Bmp-4 signaling is involved in the formation of enamel
knot.

 Bmp-4 induces the expression of - p21
Bmp-2
Msx-2
 Programmed cell death……APOPTOSIS in the knot.
 Enamel knot secretes Fgf4 &Fgf9 which stimulate proliferation
 Secondary enamel knot in multicuspid teeth

Enamel knot significance

A number of genes from different signal transduction cascades are
expressed in enamel knots.They are
 Bmp2
 Bmp 4
 Bmp7
 Fgf 9
 Wnt10
 Shh

DETERMINATION OF TOOTH POSITION.

 Genes for dental patterning are expressed in the dental
mesenchyme.
 Homeobox genes :: Msx 1, Msx 2, Dlx1, 2, 3, 5, 6, Barx
1, Otlx 2, Lhx 6, 7.
 Before E11

 Fgf 8 from epithelium Barx 1 in mesenchyme
Dlx 1 & Dlx 2
 Involved in MOLAR TEETH formation.
 Dlx1 & 2 in both mandibular and maxillaryarches.
 Bmp4 from epithelium Msx 1 &2 genes in mesenchyme
 Involved in INCISOR TEETH formation

Tooth localization genes

Schwabe C, Opitz C et all, Molecular Mechanisms of Tooth
Development and Malformations, Oral Bio sci Med 2004; 1: 77-

Irma theseff.Journal of Cell
Science 2003 (116, pp. 1647-1648

ENAMEL:
 Proteins of enamel
Ameloblastin shape & organize crystals
Enamelin
Amelogenin regulate enamel thickness
Tuftelin
Proteolytic enzymes
Enamelysin
Kallikrein-4

 Malformation of these protein leads to formation of abnormal enamel.
 Genes code all these proteins & mutation causes Amelogenesis
Imperfecta.
 AMELX, ENAM, KLK4, MMP20, &DLX3

ENAM:
 Codes for enamelin
 Mutations in ENAM leads to altered enamel
 Severe or Milder defects
 AD or AR in association with hypoplastic type of Amelogenesis
Imperfecta.
(Hart et al 2003,Rajpor et al)

AMELX :
 Codes for amelogenin
 Mutation leads to altered organization of enamel
crystals.
 Mutation inherited in an X-linked dominant or X-linked
recessive pattern.
 XLD inheritance is observed in hypoplastic type of AI
 XLR inheritance is observed in hypomaturation type AI
 AMELY (amelogenin producing gene present on Y)

MMP20:
-Code for enamelysin
-Enamelysin will cleave other proteins during maturation.
-In mutation of MMP20, enamelysin are not produced
-Thus enamel forming proteins are not cleaved and result in soft enamel with
abnormal crystal structure.
=Hypomature teeth are formed
(Li Wet al 2001)

KLK 4 :
 Codes for the protein Kallikrein
 Mutation of this gene
=Hypomaturation type of AI
(Hart et al 2004)

DLX3 : (Distal-less homeobox 3)
-Transcription factor gene which codes for Dlx 3
- Highly penetrant gene whose mutation will leads to
= Hypomaturation/ Hypoplastic/ Taurodontism type of AI

MODIFIED CLASSIFICATION OF AMELOGENESIS IMPERFECTA
INHERITANCE PHENOTYPE RELATED GENE
AUTOSOMAL DOMINANT GENERALIZED PITTED
AUTOSOMAL DOMINANT LOCALIZED HYPOPLASTIC ENAM
AUTOSOMAL DOMINANT GENERALIZED THIN ENAM
AUTOSOMAL DOMINANT HYPOCALCIFICATION
AUTOSOMAL DOMINANT WITH TAURODONTISM DLX3
AUTOSOMAL RECESSIVE LOCALIZED HYPOPLASTIC
AUTOSOMAL RECESSIVE GENERALIZED THIN
AUTOSOMAL RECESSIVE PIGMENTED HYPOMATURATION MMP20
AUTOSOMAL RECESSIVE HYPOCALCIFICATION
X-LINKED GENERALIZED THIN AMELEX
X-LINKED DIFFUSE HYPOMATURATION AMELEX
X-LINKED SNOW-CAPPED

 Dentinogenesis is a complex process in which multiple
signaling pathways converge to induce dentin formation
and is controlled by many growth and transcription
factors.

DENTIN:
 Protein of dentine - Dentin sialophosphoprotein.
 After this production,protein is cleaved into three small proteins named
DENTIN SIALOPROTEIN, DENTIN GLYCOPROTEIN, DENTIN
PHOSPHOPROTEIN.
DSPP is responsible for coding dentin sialophosphoprotein.
Dentinogenesis Imperfecta, Dentin dysplasia type2 is caused due to the
mutation of DSPP.

Raj Aswathy, MS Deepa, T Farooqi Hasan Ahmed, Brahmanandan Aswathy:Genetics and tooth anomalies -
an update, Oral Max Path J, 4(1), Jan-Jun 2013: 334-338

GENETICS IN ROOT FORMATION
Xiao-Feng Huang, Yang Chai.Molecular regulatory mechanism of tooth root
development.International Journal of Oral Science; (2012)4177–181

 Root formation -complex physiological process
 HERS dentin & cementum formation
 HERS cells do not respond to certain signals from dental mesenchyme
and do not differentiate into ameloblast.
 HERS participate in cementum formation
cementoblast
dental follicle cells

 HERS cells may provide instructive signaling to control the size, shape,
and number of roots.
(Xiao-Feng Huang, Yang Chai.Molecular regulatory mechanism of tooth root
development.International Journal of Oral Science; (2012)4177–181)

Various genes-
 TGF-β
 BMPs
 FGFs,
 Sonic hedgehog (Shh)
 Gli
 Msx1
 Msx2,
 Nfic involved in the process of root development.
 BMP and Fgf signaling in dental mesenchyme may participate in the induction of
HERS
 Tgf-β signaling in both the dental epithelium and mesenchyme also plays
essential roles in root dentin formation and root development.

Nfic is a member of the nuclear factor I family, which includes
 Nfia
 Nfib,
 Nfic
 Nfix.
 Nfic has a specific function as a key regulator of root dentin formation.
 Nfic signaling modulates late differentiation &mineralization

Shh a member of the hedgehog signaling family
 Expressed in the dental epithelium & HERS and plays an essential role during
tooth development.

 Fgf3 & Fgf10
 Expressed in the dental mesenchyme
 Help to maintain stem cell proliferation in the cervical loop of the
incisors, which continue to grow throughout life.
 Fgf10 is turned off prior to root development.
 If Fgf10 remains active in the dental papilla of the molars during root
development, the HERS will be enlarged and the root will fail to form.

 Gli-2 and Gli-3 genes are two downstream mediators of
Shh action.

SMAD 4Gene: (Tgf β signaling pathway)
Tgf β protein binds with a receptor on cell surface
Activates a group of SMAD proteins
Protein complex
Nucleus
Binds to specific areas of DNA
Regulates cell growth & division

 Smad4-mediated TGF-β/BMP signaling is required for Shh expression
in the HERS
Nfic expression in the dental mesenchyme.
 Deletion of Smad4 results in blockage of TGF-β/Bmp signaling.

Xiao-Feng Huang, Yang Chai.Molecular regulatory mechanism of tooth root development.International Journal of Oral

GENE DISORDER
DSP DENTINOGENESIS IMPERFECTA II
DENTIN DYSPLASIA II
DSPP DI TYPE III
RunX2, Osx ABNORMALITY IN ROOT FORMATION
Lhx 6 , Lhx 7 ABSENCE OF MOLAR
Dlx 3 TRICHO-DENTO-OSSEOUS SYNDROME
EGF down regulation IMPAIRED TOOTH FORMATION
Nfic ROOTLESS TEETH/ MALFORMED INCISORS
Lef Arrested Tooth morphogenesis in bud
stage.

Smad4 controls a genetic involvement of Shh and Nfic
that plays a crucial role in regulating epithelial-
mesenchymal interaction during root development

 The mesenchymal (“Classic”) hypothesis proposes that the dental follicle
cells migrate to the HERS cells on the root surface, disrupt the epithelial
structure, and differentiate into cementoblasts that form both acellular
and cellular cementum matrices .
 The epithelial origin hypothesis suggests an epithelial-mesenchymal
transformation of the HERS cells, which then differentiate into the
cementoblasts involved in forming acellular cementum and possibly
cellular cementum as well.

Runx2
 The transcription factor
 critical role in osteoblast differentiation
 take part in the signalling networks regulating tooth development.
 Lack of Runx2 allows tooth development to proceed up to the cap/bell
stage.

Osterix
 osteoblast-specific transcription factor

GROWTH FACTORS
 TGF β
 Platelet derived growth factor
 FGF
 PROMOTE CELL DIFFERENTIATION
 PROMOTE CEMENTUM FORMATION
BY ALTERING CELL CYCLE ACTIVITIES
 CELL PROLIFERATION, MIGRATION &
VASCULOGENESIS
 ENAMEL PROTEINS  EPITHELIAL-MESENCHYMAL
INTERACTIONS ALONG THE CEMENTOBLAST
PATHWAY
TRANSCRIPTION FACTORS
 Runx-2
 Osterix
 INVOLVED IN CEMENTOBLAST
DIFFERENTIATION
SIGNALING MOLECULES
 OSTEOPROTEGERIN
 RECEPTOR-ACTIVATED NF kB LIGAND
CEMENTUM SPECIFIC MOLECULES
 Cementum protein I
MEDIATE BONE & ROOT RESORPTION BY
CEMENTOCLASTS
 LOCAL REGULATOR OF CELL
DIFFERENTIATION &EXTRA CELLULAR

CONCLUSION
What it is known, however, is that transcription factors control cell fate
through a selective regulation of target genes, and that the target
gene specificity is achieved through context dependent selective
protein interactions.

REFERENCES:
 R. Maas,M. Bei:THE GENETIC CONTROL OF EARLY TOOTH
DEVELOPMENT,Oral Biol Med, 8(l),1997:4-39
 Orban.Oral Histology and Embryology.13th edition.Elsevier
 Tencates.Oral Histology.8th edition.Elsevier
 Text book of genetics.G P Pal
 Zoë Hardcastle1, Rong Mo2, Chi-chung Hui2 and Paul T.
Sharpe1:The Shh signalling pathway in tooth development:
defects in Gli2 and Gli3
mutants,Development,125,1998:2803-2811
 Hervé Acloque, MeghanSAdams,Katherine,Fishwick,Marianne
Bronner-Fraser,and M. Angela Nieto:Epithelial-mesenchymal
transitions:the importance of changing cell state in
development and disease,J.Clin.Invest.119:1438-1449(2009)
 Irma Thesleff: Epithelial-mesenchymal signalling regulating
tooth morphogenesis Journal of Cell Science 2003 (116, pp.
1647-1648)
 Isabelle Miletich and Paul T. Sharpe:Normal and abnormal
dental development, Human Molecular Genetics, 2003, Vol.
12,69-73

 Xiao-Feng Huang1 and Yang Chai:Molecular regulatory mechanism of tooth
root development, International Journal of Oral Science (2012) 4, 177–181
 Pani SC. The genetic basis of tooth agenesis: Basic concepts and genes
involved. J Indian Soc Pedod Prev Dent 2011;29:84-9.
 MELANIE McCOLLUM AND PAUL T. SHARPE:Evolution and development of
teeth,J. Anat. (2001) 199, pp. 153-159
 Marianna Bei: Molecular Genetics of Tooth Development, Curr Opin Genet
Dev. 2009 October ; 19(5): 504–510.
 IRMA THESLEFF, ANNE VAAHTOKARI, SEPPO VAINIO, AND ADRIAN JOWE’IT
Molecular Mechanisms of Cell and Tissue Interactions During Early Tooth
Development,THE ANATOMICAL RECORD 245:151-161 (1996)
 Vlasta Lungova,Ralf J. Radlanski,Abigail S. Tucker,Herbert Renz,Ivan
Mısek:Tooth-bone morphogenesis during postnatal stages of mouse first
molar development. J. Anat. (2011) 218, pp699–716
 Xiaofeng Huanga, Pablo Bringas , Harold C. Slavkina, and Yang Chaia:Fate
of HERS during Tooth Root Development, Dev Biol. 2009 October 1; 334(1):
22–30.
 Zhenhua Yang, Bo Hai,a Lizheng Qin, Xinyu Ti,Lei Shangguan, Yanqiu
Zhao,Lindsey Wiggins, Ying Liu,b Jian Q. Feng,Julia Yu Fong Chang, Fen
Wang, Fei Liua.Cessation of Epithelial Bmp Signaling Switches the
Differentiation of Crown Epithelia to the Root Lineage in a -Catenin-
Dependent Manner.Molecular and Cellular Biology2013 ;33(23):4732-4744

Genetics in tooth development

More Related Content

What's hot (20)

Similar to Genetics in tooth development (20)

Recently uploaded (20)

Genetics in tooth development

Editor's Notes