2017-2018 Essay Question Flashcards
Introduction
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- Formation and development of limbs-> embryonic development in vertebrates
- 3 limb axis-> vital or limp patterning and functionality
- axes: determine orientation and spacial organisation
- allows growth and differentiation of specialised structures.
- essay- explore development mechanisms responsible for their establishment
Understanding the 3 Limb Axis
Paragraph 1
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- 3 limb axis: refer to primary planes of orientation within developing limb bud
Proximal-distal axis
* define limb length
* >extends from proximal (closest to body) to distal (farthest) end of the limb
* Determines formation of structures:bones, muscles,tendons and limb’s strength.
Anterior-Posterior Axis
* Runs from from front (anterior) to back (posterior) of the limb
* Axis pivitol role: determining limbs symmetry and positioning of digits (fingers and toes).
Dorsal-Ventral Axis
* Extends from upper (dorsal) and lower (ventral) sides of the limb
* Develooment of specialised strctures: nails, claws or hooves.
Developmental mechanisms Producing Limb Axis (Shh)
Paragraph 2- Sonic Hedgehog (Shh) signalling pathway
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
Sonic Hedgehog signalling pathway(Shh)
* Establish anterior-posterior axis in developing limbs
* Zone of polarizinf activity (ZPA) located at posterior margin of limb bud- secretes Shh protein
* Shh protein form concentration gradient
* >high concentrations posterior side
* Cell respond differently to varying Shh concentrations
* >leads to activitation of specific genes along the anterior-posterior axis
* In turn determines the formation of individual digits and positional identity
Developmental Mechanisms Producing the Limb Axes: FGF
Paragraph 3- Fibrolast Growth Factor (FGF)
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- FGF (fibroblast growth factor) signalling pathway: proximal distal axis
- FGF10 expressed in the apical ectodermal ridge (AER) at the tip of the limb bud.
- Role in promoting limb outgrowth
- FGFs interact with their receptors - initiate signalling cascade-> promotes cell proliferation and differentiation
- Along proximal-distal axis
- Length of limb is determined by spatiotemporal regulation of FGF signalling.
Developmental Mechanisms Producing the Limb Axes: Wnt signalling pathway
Paragraph 4- Wnt signaling pathway
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- dorsal-ventral axis of the developing limb
- Dorsal and ventral ectoderm secrete Wnt proteins
- Creates signalling gradient
- Gradient influences the expression of specific genes
- Determining fate of cells along the dorsal-ventral axis
- Key role in the development of nails/claws
Developmental Mechanisms Producing the Limb Axes:Hox Genes
Paragraph 5- Hox genes
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- family of transcription factors
- Act as “master regulators” in limb development
- responsible conferring positional identity along the anterior-posterior axis
- Specific concentration and expression of Hox genes determine the distinct identities of each limb segment and digit
Conclusion
What do you understand by the three limb axes? Describe the developmental mechanisms producing the limb axes.
- 3 limb axis
- vital for vertebrate embryonic developement
- dictate spacial orientation and organisation of limb structures
- > ensure proper limb patterning and functionality
- Shh, FGF,Wnt , Hox genes ->fate of cells along different axis
Importance
* insights into limb development
* significance in broader contect of vertebrate biology
