2.5: Tissue Patterning

Question 1

define differentiation

Answer 1

the acquisition of specialized cell functions (cell fates) via differential genome expression

Question 2

t/f different cell fates require differential genome expression

Answer 2

true - through transcription regulators and regulatory modules

Question 3

state the 2 different ways cell fates can be acquired and their description

Answer 3

1. asymmetric division: daughter cells are born with different fates if you divide them correctly
2. symmetric division then perception of a signal: daughter cells are born the same and acquire different fates as a result of different influences

Question 4

which method of acquiring cell fate matches the following description: daughter cells are born with different fates if you divide them correctly

Answer 4

asymmetric division

Question 5

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

Answer 5

symmetric division then perception of a signal

Question 6

asymmetric division evenly/unevenly partitions cell date determinants before division

Answer 6

unevenly

Question 7

t/f most proteins and cellular components are distributed evenly (apart from cell fate markers)

Answer 7

true

Question 8

in asymmetric division, one child cell will inherit more of what than the other cel

Answer 8

one child cell will inherit more of this cell fate marker than the other

Question 9

what does asymmetric division require to occur

Answer 9

correct spindle alignment and cytokinesis

Question 10

t/f only asymmetric divisions can create tissue patterns (and why do u think so)

Answer 10

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

Question 11

some cells divide symmetrically to create a _______ of similar cells

Answer 11

field

Question 12

list the two mechanisms on how cell fates can be acquired from symmetric division

Answer 12

1. lateral inhibition
2. induction by diffusible signals
   the other ones are not discussed in this course

Question 13

describe what lateral inhibition amplifies

Answer 13

• 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

Question 14

what is notch signalling an example of

Answer 14

lateral inhibition

Question 15

describe notch signalling in regards to symmetric division

Answer 15

• 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

Question 16

delta _________ notch signals and notch signals __________ delta expression

Answer 16

delta activates notch signals and notch signals inhibit delta expression

Question 17

lateral inhibition creates a _________ of isolated differentiated cells

Answer 17

pattern

Question 18

diffusible signals create a _______ or ______ pattern of differentiated cells

Answer 18

band or ring

Question 19

describe how diffusible signals create a band or ring pattern of differentiated cells

Answer 19

• 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

Question 20

what type of tissue secretes morphogens/inductive signals

Answer 20

organizer tissue

Question 21

what is the banding or ring pattern dependent on

Answer 21

alignment of organizer tissues

Question 22

t/f cells can respond differently to the same morphogen given at different concentration

Answer 22

true - a morphogen gradient can form

Question 23

list what the diffusion range of morphogens are dependent on

Answer 23

how much morphogen is made, for how long, diffusion rate of the signal, stability of the signal

Question 24

t/f morphogens canNOT be indefinitely active and why

Answer 24

true - the cell remembers, you don’t need to keep telling it

Question 25

___________ experiments can identify organizer tissue

Answer 25

transplant

Question 26

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)

Answer 26

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

Question 27

are ventral or dorsal cells organizer tissue

Answer 27

dorsal

Question 28

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

Answer 28

A.
it’s not b bc you’d see bands/stripes or rings, c and d are irrelevant

Question 29

cells become increasingly differentiated as they receive more signals? define, toti, pluri, and multipotent + examples

Answer 29

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)

Question 30

multiple signals can. be combined during cell date determination, state the describe the two mechanisms

Answer 30

1. 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
2. combinatorial signaling: combos of multiple signals from the onset

Question 31

t/f does combinatorial signaling have cell memory

Answer 31

yes

Question 32

sequential induction can generate _____________________; where multiple signals can overlap to create complex patterns

Answer 32

regulatory hierarchies - gene regulation that effects other gene regulation, this can divide the body into segments

Question 33

t/f regulatory hierarchies can divide the body into segments AND lead to banding patterns (induction)

Answer 33

true

Question 34

explain how segmentation creates repeats with variation in the animal body

Answer 34

• 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

Question 35

define segmentation

Answer 35

essential process that divides the body into smaller pieces (segments), often defined by diff TF

Question 36

____ genes determine which body parts will develop from a segment, these are organized on chromosomes in order of expression

Answer 36

hox

Question 37

on drosophila hox complex (dna), hox1/2/3/4/5 define what, hox6 defines what, hox7 defines what

Answer 37

1/2/3/4/5 defines parts around the head at the ant
6 defines central
7 defines posterior

Question 38

1. hox genes encode ________________
2. how are hox genes organized on chromosomes
3. 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

Answer 38

1. transcription factors
2. into hox complexes
3. 4 copies
4. true

Question 39

loss or gain of functions in hox gene mutants can lead to?

Answer 39

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.