Lecture 14- How Cells Become Different

Question 1

differentiated cell

Answer 1

• 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.)

Question 2

cell fate/developmental fate

Answer 2

• 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

Question 3

two phases of commitment

Answer 3

• specification: committed but labile, reversible

- determination: irreversible commitment to a particular fate

Question 4

isolation experiment (not specified or determined)

Answer 4

cell isolated in a neutral environment expresses a different fate than it would normally

Question 5

isolation experiment (specified but may/not be determined)

Answer 5

cell isolated in a neutral environment expresses its normal fate

Question 6

transplantation experiment (determined)

Answer 6

placing cell/tissue in a new environment/position in embryo and it still expresses its normal fate

Question 7

transplantation experiment (not determined)

Answer 7

placing cell/tissue in a new environment/positon in embryo and it does not express its normal fate

Question 8

progressive nature of commitment

Answer 8

• each step is irreversible
• cells have memory
• cell fate becomes increasingly restricted during development

Question 9

differential gene expression theory

Answer 9

1. genome is constant in all somatic cells
2. only a small proportion of the genome in any cell type is expressed
3. unused genes that are not transcribed are not mutated or destroyed, they retain potential to be expressed

Question 10

ways to make cells different/express different genes

Answer 10

• cell intrinsic mechanisms (cell autonomous)

- cell extrinsic mechanisms (cell non-autonomous) via cell-cell communication or signaling

Question 11

cytoplasmic determinants

Answer 11

• 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

Question 12

cells born from symmetric cell division…

Answer 12

• 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

Question 13

types of signaling

Answer 13

• inductive signaling

- lateral inhibition

Question 14

inductive signaling

Answer 14

• some function in all or none manner

- some function in concentration dependent manner (morphogens)

Question 15

morphogens

Answer 15

• 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

Question 16

example of morphogen gradient

Answer 16

inappropriate expression of Shh (sonic hedgehog) or Shh signaling causes extra digit formation

Question 17

lateral inhibition (how it works)

Answer 17

1. both cells produce same amount of X and inhibit production of X in their neighbor equally
2. a transient increase in X produced by cell 1 causes a stronger inhibition of X production by cell 2
3. a decrease in X produced by cell 2 allows cell 1 to make more X

Question 18

lateral inhibition

Answer 18

works between two neighboring cells that are directly adjacent to each other, some cells predominate

Question 19

asymmetric cell division

Answer 19

cell autonomous (cell intrinsic)

Question 20

later inhibition, inductive signaling, morphogen gradients

Answer 20

• cell non-autonomous (cell extrinsic)

- require cell-cell signaling or communiation

Question 21

cell-cell signaling pathways that mediated communication in animal development

Answer 21

• transforming growth factor-beta (TGFß)
• Wnt
• hedgehog (Hh)
• Notch
• Receptor tyrosine kinase (RTKs)

Question 22

same inductive signal can generate different responses

Answer 22

• combinatorial signaling
• cell memory

both affect outcomes/expressions

Question 23

sequential induction

Answer 23

• 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