Cell Differentiation and Limb Development Flashcards
(45 cards)
What is cell differentiation?
- Process of cell changing from one cell type to another.
- Mostly, a less specialised cell to a more specialised cell
What controls cell differentiation?
- Many factors:
- Transcription factors
What are transcription factors?
-Regulators that can act at different stages and in deifferent combination through the path of cell development and differentiation.
How can cell differentiation effect a cell?
- Size
- Shape
- Membrane potential
- Metabolic activity
- Responsiveness to signals
- Different cells have different characteristics despite having the same genome
When does limb development occur?
From week 4-8
What do limbs develop from?
-Small buds of undifferentiated mesoderm cells which are covered by ectoderm
What happens/is visible by end of week 4?
- Limb buds become visible for first time
- Upper limb buds appear first as ridges from ventrolateral body wall
- Lower limb as small bulges
- Lower limb slightly behind, but catches up by end of developmental period
What is the 1st sign of limb musculature?
-Appearance of condensation of mesenchyme near limb buds
What is mesenchyme derived from?
-Dorsolateral or ventrolateral mesoderm cells of the somites
Are their nerves in the early limb bud?
NO
What do limb buds consist of?
- Mesenchymal core (from somatic layer of lateral plate mesoderm)
- Covered by layer of cuboidal ectoderm
What does the ectoderm do at the distal end of the limb bud and why is this area different?
- Forms apical ectodermal ridge
- This has inductive relationship with mesoderm and remaind undifferentiated
What is the importance of the AER?
- As limb grows the cells furthest from AER begin to differentiate into cartilage and muscle.
- Without AER limbs fail to develop as it is a key signalling centre
What initiates limb outgrowth?
FGF 10
What does the position of AER correspond to?
-Border between dorsal and ventral ectoderm
What is a difference in how UL and LL development is controlled?
Different factors designated to UL and LL
- TBX-5 in UL
- TBX-4 in LL
Describe relationship between mesoderm and ectoderm interaction and its importance?
- Essential
- AER-promote mitosis and prevents differentiation
- Although AER is acting on mesoderm, its own existence is controlled by the mesoderm
What happens at week 6 of limb development?
- Terminal portions of buds become flattened: -hand plates and foot plates
- Separated from proximal segments by constriction
- 2nd constriction further divides proximal portion into 2 segments
- Development proceeds proximodistally into 3 components
What 3 portions are limbs split to during week 6?
- Stylopod: humerus and femur
- Zeugopod: radius/ulna and tibia/fibula
- Autopod: carpals,MCP,digits,tarsals,metatarsals
What is FGF 10 and where is it first seen?
A paracrine signalling molecule 1st seen in limb buds
What is FGF family known for?
-Mitogenic activity (inducing cell to begin division via triggering a signal transduction pathway)
What signalling molecules help specify the dorsoventral axis around the AER?
- Radical fringe: expressed by dorsal ectoderm
- Engrailed-1: expressed by ventral ectoderm (TF)
What does AER express for maintenace of undifferentiated zone?
Once ridge is established it expresses FGF 4 and 8
What regulates positioning of limbs along craniocaudal axis and how is this expressed and what does misexpresion lead to?
- HOX genes
- Expressed in overlapping patterns
- Mis expression alters limb position
