What is pattern formation:
- The process in which there is a complex organisation of cell fates in space and time.
What 2 things does pattern formation require?
- Differential gene expression
2. Signalling between cells (signalling molecules)
What is cell fate?
- The developmental destination of a cell if left undisturbed in the embryo
What are the two main processes in determining cell fate?
- Cell fate commitment
a. specification
b. determination - Differentiation
What is cell fate restriction?
- When the fate of the cell becomes restricted
Describe the two factors within cell fate commitment:
a. Specification: the fate of the cell is biased but not irreversible. The cell is capable of differentiating autonomously into its specified form in a dish only- if the cell is transplanted to another part of the embryo it can change fate (as it is exposed to different factors)
b. Determination: the fate of the cell cannot be reversed. The cell will differentiate autonomously according to its determined cell fate both in a dish and if placed in another region of the organism.
What is the process of differentiation?
- The expression of developmental fate in which the cell adopts its final phenotype
- Differentiated cells express genes to form proteins to allow them to carry out their function and other exit the cell cycle
- Differentiated is usually a irreversible process (unless forced e.g. iPS cells)
What is cell fate restriction governed by?
- The cells genome (gene expression)
- The cell’s history (the factors it has been exposed to- chromatin marks)
- Interaction with its neighbouring cells
What is the difference between epithelial and mesenchymal cells?
Epithelial cells: are tightly connected to eachother in sheets/tubes, sit on a basement membrane, cannot move independently, are polarised and display epithelial marker genes e.g. cytokeratin
Mesenchymal cells: are not joined to other cells and are free to move independently around the ECM. They are not poalrised and they express mesenchymal marker genes e.g. Vimettin
What is a fate map?
- A diagram that maps adult tissues or structures to the regions of the embryo that gave rise to that tissue/structure
What are the advantages and disadvantages of invertebrate models?
Advantages:
- Easy to keep
- Rapid life cycle
- Fate of most/all cells known
Disadvantages:
- many aspects of development and anatomy are not conserved with humans
What are the advantages and disadvantages of lower vertebrate models? e.g. zebrafish
Advantages:
- Easy to keep
- Easy to manipulate and access (embryo develops outside maternal body)
Disadvantages:
- Distant from humans- some features not shared
What are the advantages and disadvantages of avian models? e.g. chickens
Advantages:
- A higher vertebrate (closer to humans)
- Easy to obtain and study (embryo develops in ovo)
Disadvantages:
- longer life cycle
- transgenic strategies lag behind those in mice
What are the advantages and disadvantages of mouse models?
Advantages:
- Mouse is a mammal- many of the same organ systems and diseases as humans
- Advanced transgenics available
Disadvantages:
- Embryos develop in utero (access is difficult)
- models can sometimes have different phenotypes as humans to disease
Describe the difference between descriptive studies and manipulative studies:
Descriptive studies:
- Observe and study the development of an organism e.g. fate mapping, histology studies etc.
Manipulative studies:
- Altering a system and observing the effects
What is differential gene expression
- Genes being turned on or off in certain cells of the embryo
- Drives pattern development and differentiation of cells
- Caused by an interaction between transcription factors and signalling between cells
What are transcription factor genes and what is an example?
- Transcription factor genes are genes that code from DNA binding proteins that have transactivation domains that bind to DNA to repress or activate genes
e. g. homeobox genes
What are HOX transcription factor genes?
- Hox genes are clusters of homeobox genes (transcription factors) (4 clusters in mammals; 1 cluster in flies)
- HOX genes are paralogues and therefore exhibit some functional redundancy
- Play a key role in patterning of head to tail segmentation of the body
What can mutations in HOX genes cause?
- Mutations in HOX genes cause homeotic transformations e.g. one body part takes on features of a more anterior body part e.g. L1 comes to resemble a thoracic vertebrae
Role of PAX transcription factors:
- Key role in development of nervous system
Role of SOX transcription factors:
- Activated by SRY gene; binds and activates genes important in determining male sex
