cell differentiation: Embryology Flashcards
Name the 2 mesodermal domains and where do the signals of each domain originate from?
Primaxial - signals from the notochord and neural tube
Abaxial - signals from the lateral plate mesoderm
What is the lateral somatic frontier?
Border between the lateral plate mesoderm and each somite
what originates from the abaxial mesodermal domain?
Thoracoabdominal muscles
what originates from the primaxial mesodermal domain?
Upper limb and neck muscles
what is a myotome (embryological)
Part of somite that develops into muscles
What is mesenchyme and where does it arise from?
Type of connective tissue found mostly during the development of an embryo. Arises from mesoderm
what is cell differentiation?
Process of a cell changing from one cell type to another
In what week does the 4 limbs form?
week 4
What does a limb bud consists of?
A mesenchymal core (from the parietal/somatic layer of lateral plate mesoderm)
Covered by a layer of cuboidal ectoderm
What does the ectoderm at the distal border of the limb bud thicken to form?
Apical ectodermal ridge
What is the apical ectodermal ridge? What occurs there and what arises from it?
Key signalling centre
Rapidly proliferating as it is undifferentiated
Where digits from from
What signal initiates limb growth and where does it originate from?
FGF 10
comes from lateral plate mesoderm cells
What signal does the dorsal ectoderm release?
Signalling molecule: Radical fringe
What signal does the ventral ectoderm release?
A transcription factor: Engrailed-1
What signals does the AER express? What do they do?
FGF 4
FGF 8
They maintain the undifferentiated zone in the apical ectodermal ridge
What starts differentiation of the proximal (shoulder) part of the limb?
Retinoic acid
What is the AER controlled by?
Mesoderm
what process occurs from week 4-8?
Limb morphogenesis
What happens to the limb bud at week 6?
Terminal portion becomes flattened to form hand plates and footplates
In what direction does the limb develop?
Proximodistally
What are the 3 components that the limb develops into? give examples for the leg and arm
Stylopod e.g. humerus OR femur
Zeugopod e.g. radius/ulna OR tibia/fibula
Autopod e.g. carpal/metacarpal, tarsal/metatarsal, digits
What gene is expressed in overlapping patterns along the length of the whole limb ?
HOX 9
What do the T-box family transcription factors do?
TFs that differentiate the upper and lower limbs
What T box- transcription factor differentiates the upper limb?
TBX-5
What T box- transcription factor differentiates the lower limb?
TBX-4 and PITX-1
When does apoptosis of the AER occur and what does it allow?
When limb bud has proliferated enough to grow a limb.
Describe digit formation
Apoptosis occurs in the AER to separate ridges into 5 parts (5 digits)
Mesenchyme condenses to form Cartilaginous digits.
By what day is digit formation complete?
Day 56
When does limb rotation occur? describe it
Week 7
Upper limbs rotate 90 degrees laterally
Lower limbs rotate 90 degrees medially
In limb bone development, expression of what signalling molecule drives cells to differentiate into chondrocytes?
BMP
At what week does bone ossification occur?
Week 8
By what week is the primary ossification centre formed?
12
Define appositional growth?
increase in width of bone
Define interstitial growth?
Increase in length of bone
How is endochondral ossification different to • Intramembranous ossification
EO: cartilage model is laid down as a precursor to bone
IO: does not involve cartilage
