L13 - Chondrogenesis Flashcards
What is the cranioacial skeleton derived from
Cranial neural creast cells
What skeleton is derived from the somites
Axial skelton
What is the limb skeeleton derved from
Lateral mesoderm
What is the axial skeleton derived from
Somites
What are components of the axial skeletons
Vertebral coliumns
Ribs
What is the axial skeleton formed from
Paraxial mesoderm - from the somites
What genes control segement idnetiy
Hox
what gene gives the boundary between the cervical and liumbar vertebrae
Hox C5 and Hox C6
As well as segement identity what else do the Hox genes control
Cell proliferation
What are the three main steps which lead to the formation of axial skeleton
Sclerotome induction
Cartilage formation
Ossification of axial skeleton
Where is the sclerotome induced
The ventral domain of the somite
What does the dorsal domain of the somite form
Responsible for the formation of muscle
Ossification of the axial skelteton is known as
Ossification
What is the order of cells that are involved in chondrogenesis
Stem cells Sclerotomal cells Chondroblasts Chondrocytes Hypertophic chondrocytes
Describe specification in chondrogenesis
Stem cells to sclerotomal cells
Describe determination in chondrogenesis
Sclerotomal cells to chondroblasts
Describe differentiation in chondrogenesis
Sclerotomal cells to chondrocytes
Describe maturation in chondrogenesis
Chondrocytes to hypertrophic chondrocytes
Pax stands for
Paired box genes
What pax genes involved in myogensis
Pax 3/7
What Pax genes involved in chondrogenesis
Pax 1/9
What is the difference between Pax 1/9 and Pax 3/7
Pax 1/9 has the single DNA binding domain
What is the first question that must be adressed when llooking at whether Pax 1/9 have a role in chondrogenesis
Are they expressed at the right place at the right time
Where are Pax 1/9 expredded
In the ventral somite as it undergoes and epithelial to mesenchymal trnasition
Describe the expression of Pax1
More strongly expressed in the medial domain
Describe the expression of Pax9
More storngly expressed in the lateral domain
Describe the phenotype of a Pax1 KO mouse
Mice viable
Abnormalities seen in vertebral column, sternum and scap
What skeleton is affected in a PAX 1 Knockout
Axial skeleton
What is the phenotypic effect of a Pax9 KO
Mice die shortly after birth
Skeletal abnormalities
What skeletons are affect in a Pax9 KO
Craniofacial, visceral and limb skeletons
What is the pheenotype of a double Pax 1/9 KO
Mice completly lack derivatives from the medial sclerotome
What structures are mssing in the Pax 1 and 9 double KO
Vertebral bodies, intervertebral discs and proximal ribs
What are Pax 1/9 required form
Development of the medial sclerotome
What strucutures remain as normal in the Pax 1 9 knockout
Neural arches
Neural arches derived from the
Dorsal slcerotome
Ventral bodies derived from
Medial sclerotome
Proximal rib deriived from the
Lateral sclerotome
Distal vertebral ribe derived from the
Medial dermomyotome
Sternal rib derived from the
Lateral dermomyotome
What two signals are reuqired for the formation of the scleretome
Shh
BMP4
What is the function of Shh in sclerotome formation
diffuses into the ventral part of the somite inducing expression of Pax 1 and 9
An Shh mutant phenotype is similar to what other KO - why?
Similar to Pax1/9 KO
Since Shh is required to induce the expression of Pax1/9 there is no induction `
BMP4 from the ….
What is its role
Lateral plate
Restricts the diffusion of Pax1
Pax1 is found in the _______
this is due to the action of
Medial domain
BMP4 from the lateral plate mesoderm
Somites generate the
Axial skeleton
Pax1/9 are essential for the
Formation of the axial keleton
Shh and BMP4 are involved in the
Induction and patterning of Pax1/9 expression
What 3 key events happen in the sclerotomal cells
Migration of the cells around the notochord
Downregulation of Pax1/9
Condensation of cells (expression of ECM proteins)
What 3 key events happen in the chondroblasts
Proliferation induced by BMP2/4/5
Production of the cartilage matrix
This requires Sox9
Proliferaition of the chondroblasts requires
BMP2/4/5
Production of the cartilage matrix requires
Sox9
What is sox9
A HMG box transcription factor
To form the vertebrae _________ cells ______ around the _______-
Sclerotomal cells
Condensate
Neural tube
How many methods of ossificiation
2
Name the two methods of ossification
Intramembranous
Endochondral
What is intramembranous ossification
Where no cartilage is formed - direct to bone
What is the steps in intramembranous ossification
Mesenchymal –> nodules –> Osteoblasts –> Osteocytes –> Bone
Where is intramembranous ossification used most commonly
Ossification of the bones of the skull
What is the 2nd method of ossification
Endochrondral method
Where is endochondral ossification most commonly seen
Most bones - e.g. the limbs
What is they key point RE endochondral ossiication
Bone develops through the replacement of cartilage
Process of endochondral ossification
Chondrogenesis formation of a cartilagenous model of the bone
Chondrocytes stop dividing and become hypertrophic
Death of chondrocytes - space invaded by BV and osteoblasts - BONE MARROW
Osteoblasts replace cartilage and form the primary ossification centre
Blood vessels enter the epiphyses
Secondary ossification centres formed in the cartilage plate between epophyssi and diaphysis
Whilst endochondral ossification is occuring what can be said of the extremities
Left untouched
One region remains untouched - what is this
Growth plate
What does the growth plate have a role in
Post natal growth of bones
What is the significance of the condrocytes undergoing apoptosis
Allows the invasion of blood vessels and osteoblasts
Formation of the bone marrow
What is CD
Campomelic dysplasia
CD caused by a mutation in
Sox9
What is the phenotype shown by Cd
Dominant
Describe what would be seen by a person (-/-) for Sox9 –> has CD
Babies die during perinatal due to skeltal abnormalities CARTILAGE DEFECTS
What skeltal abnormalities
Airway cartilage is deffective, ribcage small, vertebrae are abnormal
Mice heterguos for Sox9 exhibit
Most of the abnormalities seen in CD patients
What is the molecular mechanism involving Sox9 which gives rise to CD
Sox9 may inhibit maturation of proliferating cells
Sox9 can bind and activate promoters of chondrocyte-specific genes - Sox9 an important regulator of differentiation and maturation of chondrocytes
CCD
Cleoidocranial dysplasia
CCD caused by mutations in
Runx2
Inheritance pattern of CCD
Dominant
CCD characterised by defects in
Endochondral and intermemranous ossification
Runx2 is a
Critical regulator of bone formation
Crtical TF for toblast and chondrocyte MATURATION
What does Runx2 interact with
Osterix
What is osterix
A ZF TF exp in the osteoblasts
What is seen in Osx deficient mice
Complete absence of oseotblast differentiation but no abnormaliity in chondrocytes dif and mat
What is the action of Sox9 on mesenchymal cells
Condensation
What is required for mesenchymal condensations to form chondrocytes
Sox9, Sox5, Sox6
What is required for the maturation of chondrocytes to hypertrophic chondrocytes
Runx2
What can inhibit the maturation of chondrocytes
Sox9
What is required for mesenchymal condensations to form osteoblasts
Runx2 Osterix
What is required for osetoblasts to form osteocytes
Runx 2 and osterix
The action of Sox9/5/6 on mesenchymal condensations has what effect
Formation of chondrocytes
Effect of RunX2 on chondrocytes
Inhibits maturation
Effect of Runx2 and osterix on mesenchymal condensation
Formation of osteoblasts
Effect of RunX2 and osterix on osteoblasts
Formation of osteocytes
Growth of long bones depends on the
Growth plate
What is contained within the growth plate
All of the progenitors required
What is the signalling pathway involved at the growth plate
FGFR3 -/ Ihh –> PTHrP
PTHrP
Parathyroid hormone related protein
Signalling in the growth plate is an example of
Negative feedback
Describe the effect ON THE SIGNALLING PATHWAY of a gain of function mutation in FGFR3
Constant inhibition of Ihh so no PTHrP
What is the phenotypic effect of a gain of function mutation in FGFR3
Consitiuite activation leads to dwarfism since there is promotion of chondroblasts but these fail to form bones
Mutations in PTHrP cause …
Why?
Dwarfism
Fail to control the maturation of chondroblasts into chondrocytes
Ihh is important for the
Production and secretion of PTHrP
What is the mechanism for maintainining a continuous pool of progenitors in the growth plate
Prehypertrophic chocndrocytes secrete Ihh
Acts of the perichondrium
Release of PTHrP
PTHrP prevents progression of chondroblasts
Maintains a pool
What may also be present to aid the post natal grwoth of the muscle
Stem Cells
