Movement Lecture 5: Limb embryology Flashcards
During which weeks of development does limb development occur?
Weeks 4-8
Which section of the mesoderm is the core tissue of the limb bud initially derived from?
Lateral plate mesoderm
What does the mesoderm differentiate into in the limb bud, and what will this eventually form?
Mesenchyme
Bones and connective tissue
Which section of the mesoderm is skeletal muscle derived from?
Paraxial mesoderm
Which section of the mesoderm forms somites?
Paraxial mesoderm
During which week do the somites divide to form a sclerotome and a dermomyotome?
Week 4
Which of the sclerotome and dermomyotome is formed by the ventral somite and which is formed by the dorsal somite?
Ventral somite -> sclerotome
Dorsal somite -> dermomyotome
What is formed from the sclerotomes?
Vertebral column
What is formed from the dermomyotomes?
Dermis of the skin and skeletal muscles
During which week do the myotomes divide?
Week 5
Which sections are formed by the division of the myotomes?
Epimere
Hypomere
Which of the epimere and hypomere is dorsal and which is ventral, and which muscles will they form?
Epimere = dorsal, will form intrinsic back muscles that are innervated by the dorsal rami Hypomere = ventral, will form all other skeletal muscle that is innervated by the ventral rami
By which week have the hypomeres formed anterior and posterior condensations?
Week 7
What is the general function of the muscles derived from the anterior condensation of the hypomere in the leg?
Flexors and adductors
What is the general function of the muscles derived from the posterior condensation of the hypomere in the leg?
Extensors and abductors
During which weeks do the limbs rotate?
Weeks 6-8
In which direction do the lower limbs rotate during development and by how many degrees?
90 degrees medially
Which tissue secretes Fgf10?
Mesenchyme
What is induced by Fgf10?
Formation of the ectoderm to form the apical ectodermal ridge at the tip of the limb bud
Which fibroblast growth factors are produced by the apical ectodermal ridge?
Fgf 4 and 8
What is induced by the fibroblast growth factors produced by the AER?
Mesenchyme proliferation to form the progress zone
Which direction does the growth induced by Fgf10 occur in?
Proximodistal
What condition is induced by introducing Fgf-soaked beads into an embryo?
Supernumeracy of the limbs
In dorsoventral patterning, what is expressed by the dorsal ectoderm?
Wnt7
In dorsoventral patterning, what is expressed by the ventral ectoderm?
Engrailed-1
What is the effect of engrailed-1 on Wnt7?
Inhibitor
Which of engrailed-1 and Wnt7 will cause the formation of the sole of the foot or the palm of the hand?
Engrailed-1
What would happen to the foot if Wnt7 was improperly expressed?
Soles would form on both sides
What is the area of the mesenchyme that controls craniocaudal patterning called?
Zone of polarising activity
Is the zone of polarising activity located cranially or caudally in the limb bud?
Caudally
What is expressed by the zone of polarising activity?
Sonic hedgehog (Shh)
What does low concentrations of Shh induce?
Formation of cranial structures in the limb bud eg. thumbs and big toes
What does high concentrations of Shh induce?
Formation of caudal structures in the limb bud eg. little fingers and toes
What condition can be seen if the zone of polarising activity is transplanted so it is present both cranially and caudally in the limb bud?
Mirror image polydactyly
During which week do the terminal limb buds flatten to form hand and foot plates?
Week 6
What process in the AER causes digit formation?
Apoptosis
What is the name for the complete absence of limbs?
Amelia
What is amelia caused by?
Early loss of Fgf signalling
What would cause meromelia?
Partial or late loss of Fgf signalling
What is the name for the partial absence of limbs eg. only present up to the elbow?
Meromelia
What is phocomelia?
Digits developing prematurely, with a lack of proximal limb structures
“Flipper limb”
What malformation can be caused by thalidomide?
Phocomelia
What does thalidomide inhibit?
Fgf 8+10
What happens if apoptosis in the AER fails?
Syndactly - fused digits
What is the name for the presence of extra digits and what causes it?
Polydactyly
Inappropriate Shh expression
What is the medial name for a “lobster claw” deformity?
Ectrodactyly
What malformation can develop when the middle of the AER fails to form properly
Ectrodactyly
