Growth 2 - Anisotropic Growth

Question 1

What is morphogenesis?

Answer 1

Cells and tissues forming their shape

Question 2

Explain nutrient distribution across tissues

Answer 2

• cells on the outside are more likely to get nutrients
• cells on inside - less nutrients - less growth

Question 3

Explain cell branching on agar of different stiffness and nutrient availability

Answer 3

• low nutrients, low stiffness - skinny long branches - branching to find nutrients
• high nutrients, low stiffness - lots of branching off other branches
• low nutrients, high stiffness - mild branching, not much sub branching - branching to find nutrients
• high nutrients, high stiffness - insane branching off of each other

Question 4

Explain directional cell division in plant cells

Answer 4

• divide vertically until reaching 3 cells vertically
• then the bottom cell will divide horizontally
• cells will then continue to divide vertically
• cells at the bottom will divide vertically and horizontally periodically

Question 5

Name 3 different division of plants

Answer 5

• periclinal -> increasing radius
• anticlinal -> increases circumference
• transverse -> increases length

Question 6

Explain the divisions in WT vs the Schizoriza mutant in plant root

Answer 6

WT
- single periclinal division
- several anticlinal divisions

Schizoriza mutant
- extra periclinal divisions - extra layers
- anticlinal divisions then happen
- too much girth

Question 7

What is Herwig’s rule?

Answer 7

in the absence of overriding factors, cells orientate their division planes in the direction that will reduce mechanical stress in tissues

Question 8

What is the direction of cell division when they are not crowded?

Answer 8

random

Question 9

What is piezo 1?

Answer 9

a receptor

Question 10

What is the role of piezo 1?

Answer 10

• when cells are under tension opens a calcium chamber in the membrane
• calcium comes into cell
• cells undergo mitosis
• releasing tension on cells as more cells
• when cells are compressed it leaves the membrane and collects in the cytoplasm
• cells then leave the epithelium

Question 11

Explain the role of piezo 1 in the villi

Answer 11

• stem cells at the bottom under tension, so they will divide
• cells at the top are under compression, so they will leave

Question 12

What is the mesentery?

Answer 12

it holds the intestine to the wall of the stomach

Question 13

Explain the relationship between the gut and the mesentery

Answer 13

• proliferation in the gut is much higher than proliferation in the mesentery
• this is what forms the curves and spirals in the gut

Question 14

Explain the two different polarisations in epithelia

Answer 14

• apico-basal (z-axis)
• planar polarity (x-y plane)

Question 15

Explain how epithelial sheets keep their north and south polarity

Answer 15

• strabismus inhibits disheveled on the south side of a cell
• disheveled will be active at both of cell as there is no strabismus
• disheveled activates frizzled (north), this then activates more disheveled
• frizzled at both of one cell interacts with strabismus at south end of connecting cell

Question 16

What is the effect of cell polarisation on cell division?

Answer 16

• astral microtubules trapped by localised cortical microtubule binding proteins
• these trapping complexes interact with north and south poles if the cell
• they are pulled towards nuMA/dynein complexes
• this controls the plane in which the division happens and therefore the direction the tissue will grow in
• this is also where cell-cell junctions are so division cannot happen diagonally

Question 17

give an example where cell polarity is really important

Answer 17

• neural tube closure
• epithelium on either side of neural tube needs to be dividing horizontally to push it closed

Question 18

What is spina bifida?

Answer 18

incorrect closure of the neural tube