2.5: Tissue Patterning Flashcards
define differentiation
the acquisition of specialized cell functions (cell fates) via differential genome expression
t/f different cell fates require differential genome expression
true - through transcription regulators and regulatory modules
state the 2 different ways cell fates can be acquired and their description
- asymmetric division: daughter cells are born with different fates if you divide them correctly
- symmetric division then perception of a signal: daughter cells are born the same and acquire different fates as a result of different influences
which method of acquiring cell fate matches the following description: daughter cells are born with different fates if you divide them correctly
asymmetric division
which method of acquiring cell fate matches the following description: daughter cells are born the same and acquire different fates as a result of different influences
symmetric division then perception of a signal
asymmetric division evenly/unevenly partitions cell date determinants before division
unevenly
t/f most proteins and cellular components are distributed evenly (apart from cell fate markers)
true
in asymmetric division, one child cell will inherit more of what than the other cel
one child cell will inherit more of this cell fate marker than the other
what does asymmetric division require to occur
correct spindle alignment and cytokinesis
t/f only asymmetric divisions can create tissue patterns (and why do u think so)
false! both asymmetric and symmetric division can create tissue patterns because some cells symmetrically divide to create a field of similar cells and other cells divide asymmetrically to create several different cell types
some cells divide symmetrically to create a _______ of similar cells
field
list the two mechanisms on how cell fates can be acquired from symmetric division
- lateral inhibition
- induction by diffusible signals
the other ones are not discussed in this course
describe what lateral inhibition amplifies
- lateral inhibition amplifies small/stochastic (temporary) differences between cells
- both cells may start the same and a small/short/transient difference tips the balance
- molecular mechanisms will amplify these differences
= cells acquire different fates
what is notch signalling an example of
lateral inhibition
describe notch signalling in regards to symmetric division
- notch signalling is a form of lateral inhibition. lateral inhibition creates a pattern of isolated differentiated cells in a field of relatively undifferentiated cells
- each cells tends to inhibit its neighbor.
- each cells have a notch and delta tm prot. notch inhibits delta (same cell) and delta activates notch (other cell).
- activated notch inhibits cell specialization and inhibits delta expression
- at some point in the competition, one cells (cell1) wins and the c1 delta strongly expresses c2 notch. leading to no c2 delta on the activated notch’s (c2) cell which leads to no more delta on the opposing cell (c1).
- inactivated notch means the cell will specialize and will have delta
delta _________ notch signals and notch signals __________ delta expression
delta activates notch signals and notch signals inhibit delta expression
lateral inhibition creates a _________ of isolated differentiated cells
pattern
diffusible signals create a _______ or ______ pattern of differentiated cells
band or ring
describe how diffusible signals create a band or ring pattern of differentiated cells
- one of more cells in the organizer tissue secrete a morphogen
- morphogens are diffusible signals that can affect cell differentiation; they diffuse and act on nearby cells
- cells respond to the morphogen by taking on a new cell fate
- creates a pattern of bands/rings of different cell fates around the source
what type of tissue secretes morphogens/inductive signals
organizer tissue
what is the banding or ring pattern dependent on
alignment of organizer tissues
t/f cells can respond differently to the same morphogen given at different concentration
true - a morphogen gradient can form
list what the diffusion range of morphogens are dependent on
how much morphogen is made, for how long, diffusion rate of the signal, stability of the signal
t/f morphogens canNOT be indefinitely active and why
true - the cell remembers, you don’t need to keep telling it
___________ experiments can identify organizer tissue
transplant
describe what happens if you have two copies of organizer tissue (of dorsal) and what would happen if the opposite piece was transplanted (graft ventral cells and add to dorsal of cell 2)
creates two dorsal sides and a shared ventral side. the organizer tissue induced structures that the host would not normally make.
if the opposite piece was translated, nothing unusual would happen bc ventral cells aren’t organizer cells, they only respond to morphogen
are ventral or dorsal cells organizer tissue
dorsal
Stomata are little “mouths” on the plant surface for gas exchange. Stomata
develop via a highly regulated pattern and are carefully spaced in between
non-differentiated cells. Which mechanism is most likely involved in this
patterning?
a) Lateral inhibition
b) Induction by a diffusible signal
c) Cell migration
d) Convergent extension
A.
it’s not b bc you’d see bands/stripes or rings, c and d are irrelevant
cells become increasingly differentiated as they receive more signals? define, toti, pluri, and multipotent + examples
totipotent: can become any cell type (usually only cells very early after fert)
pluripotent: can become any adult cell type (eg blastomeres (meso, ecto, endoderm)
multipotent: can become multiple cell types (eg all tissues in gastrula)
multiple signals can. be combined during cell date determination, state the describe the two mechanisms
- cell memory/sequential signalling: starts same, experiences different morphogens to become diff cells, and aft this point, even if same morphogen they are diff cells
- combinatorial signaling: combos of multiple signals from the onset
t/f does combinatorial signaling have cell memory
yes
sequential induction can generate _____________________; where multiple signals can overlap to create complex patterns
regulatory hierarchies - gene regulation that effects other gene regulation, this can divide the body into segments
t/f regulatory hierarchies can divide the body into segments AND lead to banding patterns (induction)
true
explain how segmentation creates repeats with variation in the animal body
- most of these are transcriptional factors that act in a regulatory hierarchy
1. ant-pos
2. define head, thorax, abdomen
3. segments within head, thorax, abdomen
4. polarity within each segment
5. body parts develop from segments
define segmentation
essential process that divides the body into smaller pieces (segments), often defined by diff TF
____ genes determine which body parts will develop from a segment, these are organized on chromosomes in order of expression
hox
on drosophila hox complex (dna), hox1/2/3/4/5 define what, hox6 defines what, hox7 defines what
1/2/3/4/5 defines parts around the head at the ant
6 defines central
7 defines posterior
- hox genes encode ________________
- how are hox genes organized on chromosomes
- how many copies do humans have on answer to 2
t/f the order of hox genes on chromosomes remains the same, and the downstream targets that hox proteins activate differ between organisms
- transcription factors
- into hox complexes
- 4 copies
- true
loss or gain of functions in hox gene mutants can lead to?
hox gene mutations alter which body parts develop in a segment, so mutants cause body parts to develop in a segment where they should not normally develop.
