Lecture 14 Musculoskeletal development 1

Question 1

Describe the mesenchymal origin of each major part of the skeleton.

Answer 1

limb skeleton- interaction between the apical ectodermal ridge and the limb bud mesoderm

vertebral column- interaction between the sclerotome and the notochord of the neural tube

Head- interaction between the preskeletal neural crest cells and information along migratory paths; interactions between the brain and the overlying mesenchyme

Question 2

Be able to describe each of the major bone/cartilage differentiation pathways and the factors involved.

What are the 4 pathway?

Answer 2

1. common pathway
2. membranous bone pathway
3. permanent cartilage pathway
4. endochondral bone pathway

Question 3

Describe the origin of each part of the vertebra, including costal processes and ribs.

a. centrum
b. neural arches
c. costal processes/ribs

Answer 3

a. centrum- derived from the ventral and medial parts of paired sclerotomes
b. neural arches- arise from the dorsal regions of the sclerotomes

c. costal processes/ribs: proximal development depends on the expression of myotonic myogenic factors, Myf5 and Myf6
distal development depends on BMP signals from the somatopleural mesoderm

Question 4

Differentiate the Hox gene boundaries for the different regions of the vertebral column.

Answer 4

Occipital-cervical boundary: Hox 3

Cervical-thoracic boundary- hox6

Attached-floating ribs boundary- Hox9

Question 5

Describe results of experiments involving Hox gene knockouts.

Answer 5

-knocking out a single box gene causes homeotic transformations, one part develops into another

-

Question 6

Describe the permanent cartilage pathway

Answer 6

mesenchymal condensation forms chondroblasts

Sox-9 causes chondroblasts to secrete collagen II and cartilage; continually expressed in permanent cartilage

Question 7

Describe the origin of the sternum.

Answer 7

lateral plate mesoderm

arises from cartilaginous bones

fused bands subdivide into craniocaudal elements

Question 8

Describe the origin of the clavicle.

Answer 8

from neural crest

follows intramembranous pathway

one of the first bones to become ossified

Question 9

What is cleiodcranial dysplasia?

Answer 9

collar bones are absent or underdeveloped and the front of the skull takes a while to close

defect in RUNX2

Question 10

Describe the common pathway in the formation of bone and cartilage?

Answer 10

1. mesenchyme induced
2. production of N-cadherins to promote mesenchymal condensation
3. TGF-B stimulates synthesis of fibronectin and N-CAM
4. aggregated state of mesenchymal cells is stabilized

Question 11

Describe endochondral bone pathway

Answer 11

Runx, shh, and BMP-6 induce to undergo hypertrophy

the hyertrophic cells secrete bone proteins and vascular endothelial growth factor

the invading blood vessels erode the cartilage and brings in osteobalsts to replace the cartilage

Question 12

Describe/compare the subdivisons of the developing skull.

Answer 12

Neurocranium surrounds the brain

viscerocranium refers to the pharyngeal arches

occipital sclerotomes

Question 13

Describe the generalized neurocranium/chondrocranium.

Answer 13

surrounds the brain and has a cartilaginous and a membranous portion; base is formed from the chondrocranium which is the cartilaginous base of the neurocranium

Question 14

Describe the generalized viscerocranium and the bones that develop from the viscerocranium.

Answer 14

surrounds the oral cavity and the pharynx

has a cartilaginous portion and a membranous portion

Question 15

Describe the components of a pharyngeal arch.

Answer 15

1. skeletal elements
2. muscles
3. branch of a specific cranial nerve
4. artery

Question 16

Describe the origin of the various endochondral skull bones.

Answer 16

Membranous portions of the viscerocranium

Question 17

Define fontanelle and describe the pathway leading to the closure of fontanelles.

Answer 17

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