Module 3a Differentiation

Question 1

Differentiation

Answer 1

The process by which an unspecialized cell becomes specialized into one of the many cell types that make up the body.

Question 2

Commitment

Answer 2

=restricting cell fate
Describes a state in which a cell’s developmental fate has become restricted even though it is not yet displaying overt changes in cellular biochemistry and function. (The cell may not look different – but it is now more limited as to what it will become)

two stages to it
1) Specification
-1st stage
-cell does it autonomously (on its own) when placed in neutral environment
-commitment can still be reversed here (if placed in non neutral environment)

2)Determination:
-2nd stage
-irreversible
-able to differentiate autonomusly even when placed ni NON NEUTRAL environment

Question 3

How to differentiate if a cell is in specified or determination stage

Answer 3

Place in non neutral environment
-if able to differentiate on its own, it is on determination

Question 4

Order differentiation, detmerination andspecficiaton

Answer 4

Specification -> determination then differentation

Question 5

As a cell becomes determined

Answer 5

parts of its genome become off limits:
lose transcriptional access to certain developmental program
-lose competence to respod to certain inductive signalling

Question 6

What are the three ways in which cells become specified (1st stage of commitment)

Answer 6

1) Autonomous specification
-Cells know fate based on info within cell, do not depend on other cells or external factors
-have morphogenetic determinants (molecules that determine fate) that are unevenly spread in egg
-invariant (unchangeable )cleavage causes same lineage in all embryo (meaning all embryos have the same cell arrangement and types in all embryos of species)
-Mosaic development (each cell has a specific and irreplaceable role. if a cell (blastomere) is removed from embryp, it cannot replace it by changing the fate of other cells, so it would be incomplete development)
-blastomere fates are invariant (they know what they are and wont change it)
-if u were to take out each blastomere of embryo adn grow it isolation, it would still development into the structure it would have if it was in embryo (due to blastomere invariance, knows what it is, regardless of outer factors)

2) Conditional Specification:
-cells achieve fate through interactions with other cells
-cell-cell interaction and relation position is key
-cleavage divisions variable and fate FLEXIBLE
-cell arrangment and migrations happen before specification
-REGULATIVE DEVELOPMENT: if a blastomere of embryo lost, it can compensate
-cells adapt to new evironment and surrounding cells can recover things

3) Synctial Specification:
-start in synctium
-interactions of nuclei and transcription factors result in specification
-variable cleavage (so no rigid cell fates for any partivular nuclei, distribution random(
-after cellularization (individual cells formed from multinuclei), autonomous and conditional used
-location before cellularization determines how much of morphogen is in each cell at those points

Question 7

Transplant vs Abalate

Answer 7

transplant: take cells and move it somewhere else

abalate: remove cells completely

Question 8

Driesch vs Roux experiment

Answer 8

Roux: stuck a hot needle into 2 cell stage snd half the cell became dead, half embryo
-example of mosaic development and autonomous specfiication

Driesh: seperated 4 cells of embryo adn let them grow, still turned into a variation of what it would have when kept together so showed conditional and regulative development (slide 17)

both experiments are very different but shows us that embryos can use combination of both autonomous and conditional specifications

Question 9

Morphogens

Answer 9

substances that by their differing concentrations, differentially specify cell fates
-made in specific sites of embryo and form conc gradients from point of synthesis to other points
-different conc of morphogens can activate different genes

Question 10

Syncytium vs synctial blastoderm

Answer 10

both are describing essentially the same thing
its just a type

multinuclei reside in common cytoplasm as a result of karyokenesis (nuclear division) w/o cytokenesis or cell fusion

Synticial blastoderm: like in drosophila embryo since no cel membrane exists other than that of egg itself