BIO230H1 Lecture Notes - Lecture 17: Notch Signaling Pathway, Morphogen, Sonic Hedgehog
How do multicellular organisms develop?
Lecture 17: Tissue patterning
Multicellular development
1. Morphogenesis
- The generation of tissue shapes that form organs and bodies
2. Cell differentiation
- The generation of the different cell types in tissues
Cell Differentiation
Two main mechanisms
- Asymmetric division: sister cells born different
- Symmetric division: sister cells become different as result of influences acting on
them after birth
Asymmetric cell division and cell differentiation
- Partitions cell fate determinants to define the germline (sperm, egg cells) and other
tissues
- Requires asymmetric determinants (determines asymmetry) and proper spindle
alignments
o Cell must be split in a certain way
- E.g. of asymmetric determination: particular protein may go to one side; when cell
splits, one side has protein and on side does not
- E.g., C. elegans, forms the gut
Extrinsic mechanisms of cell differentiation
1. Direct lateral inhibition
- Creates a pattern of isolated differentiated cells (some cells differentiate and some
don’t)
- Cells begin equal, and all have transmembrane protein
- Some cells randomly gain an advantage
- These advantage cells differentiate and inhibit their neighbours from differentiating
- E.g., lateral inhibition by Notch signaling
o Each cell tends to inhibit its neighbour
o Delta activates Notch receptor in neighbouring cell
o Activated Notch inhibits its own cell specialization and Delta expression; thus,
the previous cell has no Notch activation
o Competition: one cell wins – cell differentiates and specializes
2. Induction by diffusible signals
- Cells begin with equal potential
- A diffusible signal from a group of cells drives neighboring groups into distinct
developmental pathways – creates a pattern of bands of differentiated cells
- Morphogens:
o Secreted inductive molecules that spread in a gradient
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BIO230H1 Full Course Notes
Verified Note
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Document Summary
The generation of tissue shapes that form organs and bodies: cell differentiation. The generation of the different cell types in tissues. Symmetric division: sister cells become different as result of influences acting on them after birth. Partitions cell fate determinants to define the germline (sperm, egg cells) and other tissues. Requires asymmetric determinants (determines asymmetry) and proper spindle alignments: cell must be split in a certain way. E. g. of asymmetric determination: particular protein may go to one side; when cell splits, one side has protein and on side does not. Extrinsic mechanisms of cell differentiation: direct lateral inhibition. Creates a pattern of isolated differentiated cells (some cells differentiate and some don"t) Cells begin equal, and all have transmembrane protein. These advantage cells differentiate and inhibit their neighbours from differentiating. A diffusible signal from a group of cells drives neighboring groups into distinct developmental pathways creates a pattern of bands of differentiated cells.
