Lecture 21: Limb Development 1 Flashcards
What is considered the actual primordium of the limb?
Limb disc
If the limb disc is removed, can a limb still form?
Yes, via the morphogenetic field around the disc
T/F: If the limb field is removed, no limb will form.
True
Removing half the disc, dividing the disc into two halves, & fusing two discs together results in…?
Normal limb development
What initiates future forelimb development?
Tbx5
What initiates future hindlimb development?
Tbx4 & Pitx-1
What are the initial initiators of limb development?
Tbx5 & Tbx4
Expression of which molecules forms AP axis?
Gli-3 (anterior)
Hand-2 (posterior)
The AP axis is fixed _____ in development & the DV axis is fixed _____ in development.
Early
Later
What happens if you transplant a limb disc to the opposite side?
Normal limb forms with the AP axis reversed
What happens if you rotate a limb disc 180 degrees?
Normal limb forms with AP axis reversed
What did Slack establish via his “flank tissue” experiment?
Flank tissue posterior to limb disc organizes posterior edge of the disc (posterior organizing region)
What substance provides the gradient for the posterior organizing region?
Shh, activated by retinoic acid
T/F: The ZPA is the posterior organizing region in birds.
True
What signaling molecule determines the position of the ZPA?
Hoxb8
What does Shh induce the expression of in the ZPA?
Gremlin
How does Gremlin affect the posterior part of the limb bud?
Inhibits BMP-2 which inhibits FGF-4 in AER
Inhibits Gli-3
What is expressed in the anterior part of the limb bud to make the anterior part different from the posterior part?
Gli-3
What do the dorsal and ventral parts of the ectoderm of the AER express?
Dorsal: Radical fringe
Ventral: En-1
T/F: Removal of the AER results in continued outgrowth of the limb bud.
False, results in cessation of outgrowth of limb bud
_____ determines morphology of the limb & _____ determines whether the limb grows.
Mesoderm
AER
What do cells in the distal limb bud express?
Msx-1
What creates the pattern formation in the limb?
Hoxd gene expression
Which Hox gene is expressed throughout the entire limb?
Hoxd-9
What does the stylopod form?
Humerus or femur
What does the proximal zeugopod form?
Radius/Ulna or Tibia/Fibula
What does the distal zeugopod form?
Carpals or tarsals
What does the proximal autopod form?
Metacarpals or metatarsals
What does the distal autopod form?
Phalanges
When is mesenchyme of the limb bud determined?
Before closure of the neural tube
What is the structure of the developing limb determined by?
Mesodermal components
T/F: Ectoderm tells the mesoderm what to form/make.
False, mesoderm tells the ectoderm what to form/make
What maintains the AER in a healthy state and where is it produced?
Apical Ectodermal Maintenance Factor (AEMF)
Mesoderm
AER maintains the mesodermal cells in a _____ and _____ state.
Labile
Mitotic
T/F: Apoptosis is not a mechanism for morphogenesis.
False, it is a method for morphogenesis
