Lecture 14- How Cells Become Different Flashcards
differentiated cell
- cell that has become specialized (skin, muscle, etc.)
- usually refers to terminal state of cell, but can also refer to intermediate states (mesoderm, endoderm, etc.)
cell fate/developmental fate
- refers to developmental outcome of a cell or group of cells
- cells may have become committed to a particular fate even though they may not look differentiated
two phases of commitment
- specification: committed but labile, reversible
- determination: irreversible commitment to a particular fate
isolation experiment (not specified or determined)
cell isolated in a neutral environment expresses a different fate than it would normally
isolation experiment (specified but may/not be determined)
cell isolated in a neutral environment expresses its normal fate
transplantation experiment (determined)
placing cell/tissue in a new environment/position in embryo and it still expresses its normal fate
transplantation experiment (not determined)
placing cell/tissue in a new environment/positon in embryo and it does not express its normal fate
progressive nature of commitment
- each step is irreversible
- cells have memory
- cell fate becomes increasingly restricted during development
differential gene expression theory
- genome is constant in all somatic cells
- only a small proportion of the genome in any cell type is expressed
- unused genes that are not transcribed are not mutated or destroyed, they retain potential to be expressed
ways to make cells different/express different genes
- cell intrinsic mechanisms (cell autonomous)
- cell extrinsic mechanisms (cell non-autonomous) via cell-cell communication or signaling
cytoplasmic determinants
- molecules in the cytoplasm that influence the fate of cells that receive them
- contribute to asymmetric cell division
- cell autonomous mechanism that determines cell fate
cells born from symmetric cell division…
- can adopt different fates because of influences acting on them after their birth
- cell non-autonomous mechanism that determines cell fate and is mediated by cell-cell signaling
types of signaling
- inductive signaling
- lateral inhibition
inductive signaling
- some function in all or none manner
- some function in concentration dependent manner (morphogens)
morphogens
- diffusable molecule secreted from a source (signaling cell/s)
- forms graded distribution (concentration gradient: higher near source and lower farther away)
- produces specific cellular responses depending on its local concentration
- provides a mechanism to specify fates in a reproducible pattern
- signaling molecules can function as morphogens
example of morphogen gradient
inappropriate expression of Shh (sonic hedgehog) or Shh signaling causes extra digit formation
lateral inhibition (how it works)
- both cells produce same amount of X and inhibit production of X in their neighbor equally
- a transient increase in X produced by cell 1 causes a stronger inhibition of X production by cell 2
- a decrease in X produced by cell 2 allows cell 1 to make more X
lateral inhibition
works between two neighboring cells that are directly adjacent to each other, some cells predominate
asymmetric cell division
cell autonomous (cell intrinsic)
later inhibition, inductive signaling, morphogen gradients
- cell non-autonomous (cell extrinsic)
- require cell-cell signaling or communiation
cell-cell signaling pathways that mediated communication in animal development
- transforming growth factor-beta (TGFß)
- Wnt
- hedgehog (Hh)
- Notch
- Receptor tyrosine kinase (RTKs)
same inductive signal can generate different responses
- combinatorial signaling
- cell memory
both affect outcomes/expressions
sequential induction
- for cells in order ACB, C is induced by signal from B acting on A
- for ADCEB, D and E are induced by signal from C acting on A and B respectively
