2.2 Cell Specialization

Question 1

EXPERIMENT:

injected hot needle into1 1 blastomere in 2 cell stage (dead)

Answer 1

-injected hot needle into1 1 blastomere in 2 cell stage (dead)
-gave rise to 1/2 e,bryo (only 1/2 lived and formed
example of autonomous specification
-if he had taken awau dead embryo?

Question 2

EXPERIMENT:
What happens when the blastomeres are
separated?

Answer 2

• 4 cell sea urchin =, separate, let develop each blastomere is capable of forming entire organism
• much smaller than original
• regulated conditional specification
• cells infuenced by paracrine factors around them

Question 3

Conditional Specification

Answer 3

•The cells interact with other cells to achieve their
respective cell fates.
• No macromolecular determinants of egg involved.
• Paracrine factors.
• If a blastomere is removed other neighboring cells
compensate for the missing cells.
• Usually preceded by massive cell rearrangements
(epiboly, migration or ingression).
• Predominates in vertebrates seen in few invertebrates.
• The cleavage pattern is variable no invariant fate
assigned to cells.

• if it interacts it can be influenced
• combo of autonomous and other
• take cells from back of frog and put on belly (dorsal–>ventral)–> normal tadpole
• needle remove cells –>normal tadpole

Question 4

morphogen gradient

Answer 4

•group of cells may produce a diffusible
morphogen
• If cells are close to the “source” of the
morphogen, they respond in a particular way
• If they are farther away from the source, their
response is different
• Thus cell fate is determined by a “positional”
value-positional information
•morphogen secretion doesn’t ;ead to change in position, they just take up whatever fate is dictated by [ ] they’re exposed to

Question 5

Types of inductive signals

Answer 5

• justracrine signals (1st) diffuse signal (diffusion)

* paracrine signals (2nd) interact with surface molecule (direct contact)

Question 6

Process of indictive signals

Answer 6

•Diffusion-Signal (usually a secreted ligand) is
transmitted through the extracellular space.
Examples paracrine secretions.
•Cells interact my means of molecules located on
the surface.
•Signals may pass from one cell to the next directly
through the gap junctions.

Question 7

Rate of diffusion influenced by

Answer 7

1. rate of synthesis
2. rate of degredation (if degraded than that area doesn’t nuse that morphogen)
3. rate f transport
4. stabilize the morphogen (remain in environment of embryo for a longer period of time)
5. retardation of movement

Question 8

Gradient of activin: concentration-dependent expression
of different genes in unspecified Xenopus cells
Activins

Answer 8

Activins are proteins that belong to TGF-β super family of receptors, like nodal and BMPs.
[Activin] high- activated goosecoid gene (dorsal structures).
[Activin] intermediate-activated Xbra gene (muscle cells)
[Activin] low- default genes (blood vessels).

activins, mobalized onto bead put on cells

• activin starts diffusion from beads
• decrease [ ] started expressing from xbra whch formed mesoderm blood cescles

Question 9

Syncitial

Answer 9

• Occurs in insect development.
• Early cleavage in insect embryos is syncytial, cellularization occurs later.
• Thus undetermined nuclei have their fates determined by migrating into different regions of the common cytoplasm, which contain gradients of macromolecular determinants.
• These determinants alter gene activity in nuclei
• After cellularization occurs, cell fates are mostly conditionally determined.
• nucleus divides, no cytokinesis (all are sitting in same cyto multi nuc = syncythical)
• on [ ] curve
• more caudal [ ] = tail and abdomen