tissue patterning

Question 1

differentiation

Answer 1

the acquisition of specialized cell functions via different genome expression

Question 2

how does asymmetric division unevely partition cell fate determinants?

Answer 2

some specific cell fate markers are unevenly distributed before division
after division, one child will inherit more of this cell fate marker than the other
requires correct spindle alignment and cytokinesis

Question 2

what are the different ways in which cell fate can be acquired

Answer 2

asymmetric division
symmetric division, and then perception of a signal

Question 3

what can create tissue patterns

Answer 3

asymmetric and symetric divisions

Question 4

what are the ways after symmetric division that cell fate can be acquired by?

Answer 4

lateral inhibition
induction by diffusible signals
other ways too

Question 5

lateral inhibition

Answer 5

it amplifies small stochastic difference between cells
both cells might start off the same
some tiny or short-lived difference between the two cells tips the balance
molecular mechanisms will amplify these differences
cells acquire different fates

Question 6

example of lateral inhibition

Answer 6

notch signalling

Question 7

notch signalling

Answer 7

delta and notch in each cells
notch inhibits activity of delta and cell specialzation
competition and one cell wins
cell with active delta (notch in that cell not working) specializes and inhibits its neighbour from doing likewise

Question 8

what pattern does lateral inhibition create

Answer 8

isolated differentiated cells in a field of relatively undifferentiated cells

Question 9

irl example of notch signalling

Answer 9

some fly epidermal cells will develop into sensory bristles

Question 10

what pattern do diffusible signals create

Answer 10

band or ring pattern of differentiated cells

Question 11

how does induction of diffusible signals work

Answer 11

1. one or more cells in the organizer tissue secretes morphogen
2. morphogens are diffusible signals that can affect cell differentiation, they diffuse and act on nearby cells
3. cells respond to the morphogen by taking on a new fate
4. this creates a pattern of bands or rings of different cell fates around the source

Question 12

morphogens and conc

Answer 12

cells can respond differently to the same morphogen at different concentrations

Question 13

what does the diffusion range depend on

Answer 13

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

Question 14

are morphogen indefinitely active

Answer 14

no

Question 15

what can help identify organizer tissues

Answer 15

transplant experiments

Question 16

totipotent cells

Answer 16

can become any cell type (usually only cells very early after fertilization)

Question 17

pluripotent cells

Answer 17

can become any adult cell type

Question 18

multipotent cells

Answer 18

can become multiple cell types

Question 19

what helps create cell memory

Answer 19

sequential and combinatorial signalling

Question 20

what creates regulatory hierarchies

Answer 20

sequential signalling
the same morphogen can have different effects on different cell types
this can divide the body in segments

Question 21

what do overlapping signals in anterior and posterior system do

Answer 21

determine germ cell v/s somatic cell, head vs rear and body segments

Question 22

what do overlapping signals in terminal and dorsoventral systems do?

Answer 22

determine ectoderm vs mesoderm vs endoderm and terminal structures

Question 23

segmentation

Answer 23

it is an essential process that divides the body into different pieces, it is often derived by different transcription factors

Question 24

how do transcription factors for segmentation act

Answer 24

in a regulatory hierarchy
define anterior vs posterior
define head, thorax and abdomen
segments within head, thorax and abdomen
polarity within each segment
body part develop from segments

Question 25

hox genes

Answer 25

they determine which body part will develop from a segment
they are expressed in different segments and specify different body parts
they are organized in a hox complex on chromosomes in order of expression
they encode transcription factors
the downstream targets that hox genes activate differ between organisms

Question 26

how many copies of hox gene do humans have

Answer 26

4 and the order of hox genes remains the same

Question 27

hox gene mutations

Answer 27

they alter which body part developes in a segment
loss or gain of function Hox gene mutants cause body parts to develop in a segment where they should not normally develop