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Developmental Biology > L13 - Chondrogenesis > Flashcards

L13 - Chondrogenesis Flashcards

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1
Q

What is the embryonic origin of craniofacial skeleton?

A

Cranial neural crest cells

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2
Q

What is the embryonic origin of axial skeleton?

A

Somites/paraxial mesoderm

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3
Q

What is the embryonic origin of limb/appendicular skeleton?

A

Lateral mesoderm

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4
Q

What do Hox genes control in somites?

A

Anterior-posterior patterning

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5
Q

How do hox genes work?

A

Encode identity in embryonic development
The sequential expression occurs in an anterior/posterior manor
- Determines a code that is read by cells, providing cells with a positional identity
Control of where the genes occurs is translated within the type of vertebrate

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6
Q

Example of hox gene use in chick and mouse

A

The chick has more cervical vertebra than the mouse

  • Transition between cervical and thoracic vertebrae is determined and the position is conserved between birds and mouse
  • Dictated by boundary from HoxC5 to HoxC6
  • However mouse has fewer cervical vertebra than chick so boundary shifter anteriorly
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7
Q

How can hox genes control vertebrate size?

A

Hox genes control genes involved in cell proliferation

Can couple the positional info to the amount of proliferation

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8
Q

What are the 3 steps leading to axial skeleton formation?

A
  1. Sclerotome induction - in ventral part of somites
  2. Cartilage formation – chondrogenesis
  3. Ossification of axial skeleton – osteogenesis
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9
Q

Chondrogenesis method

A
  1. Stem cells – undergoes specification
  2. Sclerotomal cells – undergoes determination
  3. Chondroblasts – undergoes differentiation
  4. Chondrocytes – undergoes maturation
  5. Hypertrophic chondrocytes
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10
Q

What pax genes are involved in chondrogenesis?

A

Pax1/9

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11
Q

What pax genes are involved in myogenesis?

A

Pax3/7

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12
Q

What genes are expressed during sclerotome formation?

A

Ventral part of somite undergoes epithelial-mesenchymal transition
Pax 1 and Pax 9 genes are exclusively expressed by sclerotome cells

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13
Q

In sclerotome cells is Pax1 expressed more medially or laterally?

A

Medially

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14
Q

In sclerotome cells is Pax9 expressed more medially or laterally?

A

Laterally

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15
Q

Pax1 knockout phenotype?

A

Mice are viable

Have abnormalities in the vertebral column, the sternum and the scapula

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16
Q

Pax9 knockout phenotype?

A

Mice die shortly after birth

Have abnormal craniofacial, visceral and limb skeletogenesis

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17
Q

Pax1/9 knockout phenotype?

A

Mice completely lack derivatives of medial sclerotome - vertebral bodies, intervertebral discs, proximal ribs
Distal part of ribs not affected

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18
Q

What did the Pax1/9 knockout show?

A

Pax1 or Pax9 is required for medial sclerotome development

Demonstrated the essential role in axial skeleton formation

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19
Q

Where are Pax1/9 expressed in the sclerotome and what does it form?

A

Medial sclerotome –> vertebral bodies

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20
Q

What does the lateral sclerotome form?

A

Proximal rib

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21
Q

What does the dorsal sclerotome form?

A

Neural arches

22
Q

What does the dermomyotome form?

A

Distal vertebral rib and sternal rib

23
Q

How were the derivatives of the sclerotome discovered?

A

These were all identified using the double knockout

  • Pax1 and Pax9 expressed in medial and lateral areas
  • In double knockout neural arches not affected – know that neural arches arise from dorsal aspect not expressing Pax1/9
24
Q

What signals control sclerotome formation?

A

Shh signalling from the notochord induces expression of Pax1 and Pax9
BMP signalling from the lateral plate inhibits Pax1 and Pax9
- Contributes to medial/lateral boundary
- Inhibits diffusion of Pax1 into lateral domain

25
Q

What process occur in the sclerotomal cell to convert in to a chondroblast?

A
  1. Migration of cells around notochord
  2. Down regulation of Pax1 and Pax9
  3. Condensation of cells – extracellular matrix proteins
26
Q

What process occur in the chondroblast cell to convert in to a chondrocyte?

A
  1. Proliferation induced by BMP2, BMP4 and BMP5

2. Production of cartilage matrix – requires Sox9

27
Q

What happens to the sclerotome cells around the notochord?

A

Condensation

28
Q

What are the two models of osteogenesis?

A

Intramembranous ossification

Endochondral ossification

29
Q

Intramembranous ossification method

A

Used for ossification of bones from skull

  1. Mesenchymal cells
  2. Nodules
  3. Osteoblasts
  4. Osteocytes
  5. Bone
30
Q

Endochondral ossification

A

Used for ossification of most limb bones

Bone developed by replacement of cartilage model

31
Q

Endochondral ossification method

A
  1. Chondrogenesis – formation of a cartilaginous model of bone
  2. Chondrocytes stop dividing and become hypertrophic
  3. Chondrocytes die by apoptosis - blood vessels and osteoblasts enter this space which will become bone marrow
  4. Osteoblasts replace the disappearing cartilage and form primary ossification centre
  5. Blood vessels enter the ends
  6. Secondary ossification centres and formed in epiphyses leaving a cartilage plate between epiphysis and diaphysis
32
Q

What is CD?

A

Campomelic dysplasia

33
Q

What is CCD?

A

Cleidocranial dysplasia

34
Q

What causes CD?

A

Loss of function mutation in Sox9

35
Q

What causes CCD?

A

Mutation in Runx2

36
Q

What is the phenotype of CD?

A

Leads to death of babies during the prenatal period or in early infancy
Die due to skeletal abnormalities suggesting a defect in cartilage
Many of the defects are similar to those caused by mutations in cartilage collagens II/XI
Heterozygous Sox9 null mice show most of the abnormalities seen in CD patients

37
Q

What is the phenotype of CCD?

A

Leads to defects in formation of bones and in formation of hypertrophic chondrocytes

38
Q

Runx2 studies in CDD

A

Proliferative chondrocytes not capable of proliferating
As with Sox9, Runx2 acts in two locations
Runx2 is required for the expression of osterix
- Osterix knockout only shows defects in osteogenesis not chondrogenesis
Allows you to balance osteogenesis and chondrogenesis

39
Q

Sox9 studies in CD

A

Sox9 plays a role early on in mesenchymal condensations and bone formation
Forward genetics – identify gene responsible for human phenotype – Sox9
Reverse genetics – need to tell you how the gene is controlling this process

40
Q

Condition knockout sox9 studies in mice

A

In mice – conditional knockouts
Allows you to control when and where the gene is knocked out
Knock out Sox9 at different positions and timing

41
Q

What happens if you knockout out Sox9 immediately after mesenchymal condensation?

A

Deficit in the formation of proliferative chondrocytes and therefore bones

42
Q

What happens if you knockout out Sox9 after proliferative chondrocytes have formed?

A

Reduction in the maturation of chondrocytes into hypertrophic chondrocytes

43
Q

What is special about the region in between epiphysis and diaphysis that has not been ossified?

A 
Layered organisation of cells 
Have every single cell type present 
- Proliferative chondroblasts 
- Differentiated chondrocytes 
- Pre-hypertrophic chondrocytes 
- Hypertrophic chondrocytes 
- Zone of specification 
You have cells of every single step of cartilage to bone formation
44
Q

What does the negative feedback loop between Ihh and PTHrP control?

A

Chondrocyte differentiation and maturation

45
Q

What is PTHrP?

A

Parathyroid hormone-related protein

46
Q

What do gain of function mutations in FGFR3 do?

A

Can introduce these mutations in mouse – gives the same phenotype
- Dwarfism
They promote the proliferation of chondroblasts
Make receptor constitutively active

47
Q

FGFR3 block?

A

Ihh

48
Q

Ihh activates?

A

PTHrP

49
Q

As cells progress and differentiate and mature the pre-hypertrophic chondrocytes secrete?

A

Ihh

50
Q

What is the role of Ihh?

A

Induces production of PTHrP
Inhibits further progression to hypertrophic chondrocytes
Promotes differentiation of cells earlier on– induced chondroblast proliferation
- Negative feedback loop
Maintain a pool of progenitor cells in the growth plate for future muscle growth

Developmental Biology (16 decks)

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