Diff9 - 16 Flashcards
Where does the craniofacial skeleton come from?
Cranial neural crest
Where does the axial skeleton come from?
Somites
Where does the limb skeleton come from?
Lateral mesoderm
What is essential for axial skeleton formation?
Pax1/9
What supplements sclerotome formation?
Scleraxis
What are involved in patterning of Pax1/9 expression?
SHh and BMP4
What are the three steps in axial skeleton formation?
Sclerotome induction, chondrogenesis, osteogenesis
Outline sclerotome induction
Characterise Pax1 KO
Viable, abnormalities in vertebrae, sternum and scapula
Characterise Pax9 KO
Die early, abnormal craniofacial, visceral and limb skeletogenesis
Characterise Pax1/9 KO
Completely lack medial sclerotome derivatives
Outline transformation from sclerotomal cell to chondroblast
Migration around notochord, down-regulation of Pax1/9, condensation
Outline transformation from chondroblast to chondrocyte
Proliferation induced by BMP2/4/5, production of cartilage matrix proteins
What does chondroblast production of cartilage matrix proteins require?
Sox9, HMG-box transcription factor
What are the two main modes of osteogenesis?
Intramembranous - mainly skull; endochondral - limbs
Outline endochondral ossification
Chondrogenesis; chondrocytes cease proliferation, becoming hypertrophic, then dying by apoptosis; blood vessels and osteoblasts enter this space, becoming bone marrow; osteoblasts replace disappearing cartilage and form primary ossification centre; blood vessels enter epiphyses; secondary ossification centres form in epiphyses, leaving cartilaginous growth plate between
