L4 Flashcards
Gar fish
scales made of dentin with some enamel. Also have enamel teeth.
Most fundamental aspect of enamel formation
innovation occured betwen 520 and 400 mil years ago, ameloblasts on dentin surface start to deposit ribbons to make enamel layer.
Enamel crystals are organized into
cylindrical rods (prisms) embedded in interrod enamel (interprismatic substance).
Each rod contains
~10,000 crystals, all oriented in the direction of the rod.
Sparc-L1
encodes for basement membrane protein on surface of dentin
Enamel was made in the
scales and teeth of the common ancestor of coelacanth & the gar (>450 Mya).
More than 520 Ma fish were
soft-bodied and lacked skeletons, jaws, teeth, & scales.
Earliest Fish (Chordates =
Notochord)
Vertebrate features
: a notochord, a pair of prominent camera-type eyes, paired nasal sacs, possible cranium and arcualia, W-shaped myomeres, and a post-anal tail.
The Gar
Long slender bodies covered in rock-hard ganoid scales.
Many large pointed teeth.
Can breathe air.
swim bladder they fill by gulping air to supplement their gill breathing in low-oxygen environments.
Can remain out of water for nearly 1 h without dying.
A thick coat of scales make the alligator gar the best protected fish species.
The Coelacanth: More Living than Fossil
Lobe-finned fish with lungs: close relative to amphibians
Coelacanths (seel-a-canths) were once known only from fossils and were thought to have gone extinct approximately 65 million years ago (mya), during the great extinction in which the dinosaurs disappeared. The most recent fossil record dates from about 80 mya but the earliest records date back as far as approximately 360 mya. At one time coelacanths were a large group comprising about 90 valid species that were distributed worldwide in both marine and freshwaters. Today, there are two known living species.
- Enamel Formation is a Unique
Epithelial Mineralization Process That Evolved in Response to Evolutionary Pressures for Harder Teeth & Scales.
2 The Fundamental Innovations Were to Form & Support a
Mineralization Front Apparatus Along the Secretory Surface of the Ameloblast Apical Membrane to Initiate, Extend & Orient Enamel Mineral Ribbons, and Then Harden this Mineral Layer by Thickening the Ribbons.
The secretory calcium-binding phosphoprotein (SCPP) gene family evolved by
gene duplication from a single ancestral gene (SPARC-L1).
SCPP: Two groups:
Acidic/Proline & Glutamine rich proteins
SCPP proteins: Non-collagenous proteins of
bone, dentin, and enamel; milk, salivary proteins, homeostasis, mineral inhibitor.
Human SCPP genes are clustered on
Chromosome 4.
- A patient with the following oral and radiographic presentation is likely to develop what other phenotype?
kidney calcifications
These enamel malformations were observed in a patient with no skin fragility, but she had a sibliing with enamel malformations and skin fragility. She is likley a carrier for which of these conditions?
Junctional epidermolysis bullosa
Secretory Stage:
Crystals grow in length
Maturation Stage:
Crystals thicken
Forming mineralization front;
Basement membrane of the Inner Enamel Epithelium fenestrates.
Finger-like ameloblast processes (*) penetrate into the pre-dentin (pd) matrix.
Onset of mineral foci in dentin, which coalesce into a continuous mineral layer.
If you have a problem with ribbon extension, you have
thin enamel.
Lama3-/- Mice: Defects Start at
Secretory Stage
Presecretory ameloblasts of wild-type (F) and mutant animals (J) are indistinguishable. Secretory ameloblasts are
pathological (K).
Enamel mineral ribbons initiate directly on
dentin mineral and most obviously onto the sides and tips of mineralized collagen fibers, and extend from there to the ameloblast membrane.
Parallel enamel ribbons run in
clusters from a common origin on dentin to a common section of ameloblast membrane.
Each cluster of enamel ribbons is initiated by a single
ameloblast process and is extended by it as the process retracts into the ameloblast distal membrane.
The orientations of the initial enamel ribbons on dentin are determined by the
path of the retrograde movement of the ameloblast membrane.
The more highly mineralized dentin contrasts with the overlying
enamel mineral ribbons, so that while this interface was highly irregular, the boundary between the two mineralized tissues was always distinct, even though the enamel ribbons were directly continuous with the dentin mineral.
Initial Enamel Mineralization
no rods initially, extends up to flattened surface from dentin.
No enamel ribbons form in
Ambn & Enam null mice. The process initiates but quickly turns pathological in Amelx and Mmp20 null mice.
SCPP all have
phosphorylation site.
FAM20C, or Golgi Casein Kinase, is a
secretory pathway protein kinase that phosphorylates the majority of the secreted phosphoproteins in plasma, serum, milk and csf, as well as many of the extracellular matrix proteins in enamel and other mineralized tissues.
FAM20A is closely related to FAM20C but does not have
kinase activity. Instead it forms a functional complex with FAM20C, which allosterically enhances FAM20C activity.
The problem with FAM20C kinase is that
all of these effected proteins are not phosphorylated - results in enamel-renal syndrome, others.
CLDN16 is an integral membrane protein component of
tight junctions. Its absence can affect the paracellular transportation of Mg2+ & Ca2+.
Ameloblasts undergo
repetitive alternations between ruffle-ended and smooth-ended morphologies throughout the maturation stage.
In rat incisors each modulation cycle lasts about
8 h (3 per day). Ameloblasts spend ~4 h as ruffle-ended, ~2 h as smooth-ended, and ~2 h re-creating the ruffled border after having been smooth-ended.
The predominant maturation ameloblast morphology is ruffle-ended. Ameloblasts initially form the ruffled border when they complete post-secretory transition at the beginning of the maturation stage and re-create the ruffled border multiple times throughout the maturation stage, following each successive smooth-ended transition.
Ameloblasts are “smooth-ended” when the apical invaginations are missing and apical junctional complexes are disassociated and leaky.
About 25% of the total ameloblast population entering post-secretory transition die in a matter of hours, leaving ~75% of the original population that formed enamel rods to initiate rhythmic modulations at the surface of the maturing enamel. An additional 25% of the ameloblast population dies as ameloblasts modulate, so that only 50% of the original population that formed enamel rods eventually finishes the maturation stage.
Because of enamel formation chemistry, you produce
acid (11 protons for every 10 calciums). This acidifies the matrix.
Smooth ameloblast
spends 3/4 time as rough, at the end the matrix is neutralized. There are cycles of acidity.
Mineralization front apparatus is replaced with a
specialized basement membrane that tightly adheres the cells to the enamel layer. Amelotin (AMTN) and ODAM contribute to this attachment.
Stromal Interaction Molecule 1 (STIM1)
STIM1 is a
transmembrane protein with Ca2+ binding domains in ER that is activated by depletion of ER Ca2+ stores. After store emptying, STIM1 forms multimers that passively migrate to ER-plasma membrane junctions where they activate the Ca2+ channel ORAI1.
- Calcium release-activated calcium channel protein 1 (ORAI1)
Together, STIM1 & ORAI1 mediate store-operated calcium entry (SOCE), which is a Ca2+ influx pathway critical for the normal functioning of many cell types, including T cells, muscle cells, and ameloblasts. Homozygous loss of function mutations in ORAI1 and STIM1 cause Immunodeficiency 9 and 10, respectively, which feature severe immunodeficiency, congenital myopathy, ectodermal dysplasia, and AI.
- Potassium-dependent sodium-calcium exchanger (SLC24A4)
Uses a Na+ gradient to transport Ca2+ out of the cell (efflux).
Mg2+ is actively pumped out by
CNNM4 in the basolateral (proximal) membrane toward the blood supply. Green = positive immunostaining for CNNM4. Red immunostains intercellular junctions.
Mg2+ passively exits the enamel layer and into ameloblasts through
channels in the distal membrane.
H+ are Released
During HAP Formation
~11 H+ for each unit cell at pH 7.2
Ameloblasts undergo repetitive alternations between
ruffle-ended and smooth-ended morphologies throughout the maturation stage.
In rat incisors each modulation cycle lasts about 8 h (3 per day). Ameloblasts spend ~4 h as ruffle-ended, ~2 h as smooth-ended, and ~2 h re-creating the ruffled border after having been smooth-ended.
The predominant maturation ameloblast morphology is ruffle-ended. Ameloblasts initially form the ruffled border when they complete post-secretory transition at the beginning of the maturation stage and re-create the ruffled border multiple times throughout the maturation stage, following each successive smooth-ended transition.
Ameloblasts are “smooth-ended” when the
apical invaginations are missing and apical junctional complexes are disassociated and leaky.
About 25% of the total ameloblast population entering post-secretory transition die in a matter of hours, leaving ~75% of the original population that formed enamel rods to initiate rhythmic modulations at the surface of the maturing enamel. An additional 25% of the ameloblast population dies as ameloblasts modulate, so that only 50% of the original population that formed enamel rods eventually finishes the maturation stage.
Structure of Calcium Hydroxyapatite
Substitution of
oH- by Fluoride
Closest structural analogue to the mineral in bones & teeth is
calcium hydroxyapatite (HAP)
The same mineral is in mineralized cartilage, bone, cementum, dentin, and enamel.
Dental Enamel is ~ 96% mineral (by Weight)
Dentin is ~ 70% mineral
Bone is ~ 65-70% mineral
Coulomb’s Law
Hydroxyapatite holds together by electrostatic interactions. The force of attraction is described by Coulomb’s law. Note that the force holding together the crystal is greatly reduced by increasing the distance between ions in the lattice
Substitution of OH- with F-
A hexagonal close packed (HCP) arrangement represents the densest possible packing of the phosphate “spheres”, which are the largest ion in HAP.
The dense packing decreases the distance between opposite charges.
There are twice as many interstices as there are PO43- ions, which provide the exact number of spaces needed for the calcium and hydroxyl ions.
Ca2+ and OH- ions occupy the interstices between phosphates, but force the phosphate ions apart slightly, so they not as closely packed as they could be.
Hydroxyl ions are larger than the calcium ions and expand the crystal structure to a greater degree. Fluoride ions are smaller than hydroxyl ions, so substituting F- for OH- allows the phosphates to achieve closer packing, increasing the stability of the crystal.
The solubility product constant (Ksp) is the ion product of a solution that is at
equilibrium with a crystal.
The ion product (Qsp) is equal to the product of the
concen-trations of the ions involved in the equilibrium, each raised to the power of its coefficient in the equilibrium equation.
The ionic product (Qsp) can depend on the
pH of the solution.
A crystal is at equilibrium with the surrounding solution when Qsp = Ksp, and the solution is said to be “saturated”.
The smaller the Ksp (higher negative exponent), the less
soluble is the crystal.
Dissolving An Ionic Solid (Salt)
The salt starts to dissociate into its component ions (dissolve).
Ions in the water begin to collide with the crystal and add back to the lattice (precipitate).
Eventually the dissociation rate equals the precipitation rate.
The solution is now saturated. It has reached equilibrium.
In solution, phosphate exists in
4 forms. The relative abundance of these 4 forms depends upon the [H+], or pH. In strongly-basic conditions, the phosphate ion (PO43−) predominates, whereas in weakly-basic conditions, the hydrogen phosphate ion (HPO42−) is prevalent. In weakly-acid conditions, the dihydrogen phosphate ion (H2PO4−) is most common. In strongly-acid conditions, aqueous phosphoric acid (H3PO4) is the main form.
