7.1 Organogenesis and Morphogenesis Flashcards
Some important processes in organogenesis:
Cellular Processes –>Molecular events
- Sorting: Homotypic adhesion
- Movement: cytoskeletal changes
- Sticking together: cellular junctions
- Alteration of shape: Cytoskeletal changes
- Cell division, death: Mitosis and apoptosis
Morphogenesis
Building of 3D structure, generation of the form that we see.
Sorting of cells: Homotypic cell adhesions,
•Cadherins are CA+2 Dependent adHesion molecules.
• Cadherin interacts with cadherins on the adjacent cells leading to cell-cell adhesion. (ex is transmembrane proteins)
• Anchored inside the cell by a complex of proteins catenins.
• Cadherin and catenin binds with the microfilament (cytoskeleton).
•Cadhersn:
-adhere cells together
-link and assemble actin sytoskelton (provide the mechanical force to make sheets and tuebs)
-signaling molecules that change a cells gene expresison
Different type of cadherins in vertebrates
E-cadherin (early embryonic cells)
P-cadherin (Placenta)
N-cadherin (Central nervous system)
R-cadherin (retina), etc.
Number of cadherin and types are responsible for the strength of cell-cell adhesion.
Integrins
- bind to extracellular fibronectin and intracellular cytoskeleton (actin)
- TMP (trans membrane protein) with an alpha and beta subunit
- allows cell to move by contracting the actin againsted the fixed extracellular matrix.
- integrins can signal from outside in altering gene expression
- Adherin junction (where one cadherin attaches to the other cad herein) basis on forming the epithelium
- ECM (extra cellar membrane) around cells
- interns NB for cell-ECM interactions
- when signalling received, alpha beta subsets are rendered apart. Heads no longer bent but straight
- 70 armstrong (70ºA)
- inactive integrin is close
Extracellular matrix (ECM): Role in gastrulation
- ECM is the matrix in between the cells occupying interstitial space.
- It helps the cells attach to one another (Cell-ECM) interaction.
- ECM is composed of proteins-collagen, fibronectin, laminin, proteoglycans, etc…
- Can also play an important role during gastrulation cell movements, cell migration.
4 Steps in Cell Migration
- Cells become polarized (form a front and rear end):
• The process involves the reorganization of actin
cytoskeleton.
• Polarisation is directed by signals (eg. chemotactic or
extracellular matrix) - Protrusion of cells leading edge:
• Polymerization of G-actin to F-actin
• Formation of filopodia.
• Signaling Rho-GTPase activated - Adhesion of the cell to the extracellular matrix (ECM):
• Integrins on cell membrane attaches to ECM (focal
adhesion) and to actins within the cell. - Release of the adhesion in the rear end
Epithilial-Mesenchyme Transition (EMT)
- EMT is Important in organogenesis as well as cancer biology.
- Cancer initiates as a epithelial cancer … later metastasize to different locations
- Epithelial sheet forms a water-proof covering, bend-sheet forms tube, etc.
- Epithelial cells are attached to each other through adheren junctions and the the basal lamina through integrins
Epithelial-Mesenchyme Interactions
Steps:
•cells attached to each other by adherens junctions with cadherin and actin rings
•intergrin attached cell to basal lamina
•signals from paracrine factors
•cell adhesion is broken and the basement membrane (basal lamina) dissolved
•cell released from basement membrane become mesenchyme
•mesenchyme can form mesoderm
Formation of neural tube
- In the mesodermal layer the notochord is formed.
- Notochord triggers the epidermal layer above to thicken and form the neural plate.
- The neural plate folds forming the neural groove.
- the neural crest is elevated and converges together
- The neural plate folds move and forms a tube that eventually pinches off from the epidermis.
- Some of the cells from the neural tube break free and form the neural crest cells that would develop the peripheral nervous system
Neural Crest gives rise to 4
1) neurons and glial cells of sensory, sympathies and parasympathetic nervous system
2) Epinephrin producing medulla of adrenal glands
3) forms melanocytes
4) many skeletal and cognitive tissues of the head
Nerulation and cadherins
- at first, all expressing E-cadherin then switch to N catherine and cells start separating (this are neural tube)
- migrating cells express neither
- N-cadherin forms neural tube/neural plate
- E-cadherein form the epidermis right on top
