Limb Development
Achondroplasia (dwarfism) – caused by fibroblast growth factor (FGF)
mutation.
Initial limb buds are composed of junior fibroblasts in a collagen mesh.
Time of development at which you trim off epithelial cell layer affects
number of limb elements that grow.
The apical ectodermal ridge produces ridge factor, this factor can only
diffuse back a certain distance known as the progress zone.
The time for which certain cells are in this zone determines their
differentiation and ultimately what they develop into e.g. humorous
measured by number of divisions they’ve undergone
Anterior-posterior axis in embryology is thumb anterior and 5th digit
posterior
In a grafting experiment where you remove some of the tissue from the
posterior side of a limb bud and graft it onto the anterior side of new limb
you get a limb that is posterior on both sides. This occurs because:
On the posterior side of the limb is the source of ZPA (zone
polarising activity)
Thus signal is high on posterior side and low on the anterior side
Cells read this gradient, telling them how to differentiate
Factor involved in gradient from posterior side is sonic hedgehog
Sonic switches BMP (bone morphogenetic protein) gene on which
produces protein that is able to diffuse further
Graft of leg bud tissue onto wing bud:
Buds are the same but genetic switch early on as to whether arm or
leg, TBOC genes are responsible
In this experiment a block of mesodermal tissue, which would have
been thigh, is graft onto the tip of the wing bud under apical
ectodermal ridge.
As it is placed under ectodermal ridge the clock restarts on block so
instead of femur, toes are produced
Based on a lecture delivered by Prof P Martin at the University of Bristol 2015
Achondroplasia (dwarfism) – caused by fibroblast growth factor (FGF)
mutation.
Initial limb buds are composed of junior fibroblasts in a collagen mesh.
Time of development at which you trim off epithelial cell layer affects
number of limb elements that grow.
The apical ectodermal ridge produces ridge factor, this factor can only
diffuse back a certain distance known as the progress zone.
The time for which certain cells are in this zone determines their
differentiation and ultimately what they develop into e.g. humorous
measured by number of divisions they’ve undergone
Anterior-posterior axis in embryology is thumb anterior and 5th digit
posterior
In a grafting experiment where you remove some of the tissue from the
posterior side of a limb bud and graft it onto the anterior side of new limb
you get a limb that is posterior on both sides. This occurs because:
On the posterior side of the limb is the source of ZPA (zone
polarising activity)
Thus signal is high on posterior side and low on the anterior side
Cells read this gradient, telling them how to differentiate
Factor involved in gradient from posterior side is sonic hedgehog
Sonic switches BMP (bone morphogenetic protein) gene on which
produces protein that is able to diffuse further
Graft of leg bud tissue onto wing bud:
Buds are the same but genetic switch early on as to whether arm or
leg, TBOC genes are responsible
In this experiment a block of mesodermal tissue, which would have
been thigh, is graft onto the tip of the wing bud under apical
ectodermal ridge.
As it is placed under ectodermal ridge the clock restarts on block so
instead of femur, toes are produced
Based on a lecture delivered by Prof P Martin at the University of Bristol 2015
