Chondrogenesis Flashcards
What are the 3 embryonic origins of BONES?
1) Cranial neural crest cells
2) Somites
3) Lateral mesoderm
What bones do the cranial neural crest cells give rise to?
The craniofacial skeleton
What bones do the somites give rise to?
The axial skeleton
What is the axial skeleton?
Trunk - ribs and vertebrae
What does the lateral mesoderm give rise to?
The limb (appendicular) skeleton
What do Hox genes do?
How?
Control the anterior-posterior patterning of somites
How?
- Organised in sequential expression in the embryo in AP fashion
- Determines a CODE that is read by cells - provides positional identity to cells
- Tells the cells what type of vertebrae to become
What does the hox code dictate?
The TRANSITIONS between the different types of vertebrae
What is the transition between the cervical and thoracic vertebrae determined by in the mouse/chick?
Hox c5
Hox c6
Why does the chick have more cervical vertebrae than the mouse?
Boundary between Hox c5 and Hox c6 is shifted more anteriorly in the mouse
How many cervical vertebraes do mammals have?
7
How do mammal vertebrae differ?
How is this controlled?
Differ in size
Controlled by hox genes:
- Control the genes that are involved in cell proliferation
What genes do hox genes control?
- Genes that control positional identity
- Genes that control proliferation
What are the 3 steps leading to AXIAL skeleton formation?
1) Scelerotome induction in the somite
2) Cartilage formation
3) Ossification of axial skeleton
Where are the sclerotome precursors in the somite?
In the VENTRAL part
What does the sclerotome form?
Cartilage and bone
What is chondrogenesis?
The formation of cartiladge
What is osteogenesis?
The formation of bone (ossification)
What are the stages of chondrogensis?
1) Start with a MULTIPOTENT cell in the somite
2) Cell becomes SPECIFIED to become a SCLEROTOMAL cell
3) Cell DETERMINED to specific lineage - CHONDROBLASTS
4) Cell DIFFERENTIATES to CHONDROCYTES
5) Cell undergoes MATURATION - to form HYPERTROPHIC CHONDROCYTES
What are the first cell types of cartilage?
Chondroblasts
What are pax genes?
Paired-box genes
What pax genes are involved in the formation of cartilage?
How is this different to muscle?
Cartilage:
- Pax 1
- Pax 9
Muscle:
- Pax 3
In sclerotomal tissue, where is pax 1 and pax9 expressed?
Where is pax1 more strongly expressed?
Pax 9?
In BOTH the medial and lateral sclerotome
Pax 1 - more medial
Pax 9 - more lateral
What is the result of a Pax 1 KO?
Abnormalities in the vertebral column, sternum and scapula
What is the result of a Pax9 KO?
Abnormalities in the skeleton of:
- Craniofacial
- Visceral
- Limb
Die shortly after birth