Lecture 4: tissue morphogenesis

Question 1

What is cell proliferation

Answer 1

increase in cell numbers via cell division

Question 2

What is cell differentiation

Answer 2

change in cell fate via cell signaling & differential genome expression

Question 3

What is cell morphogenesis

Answer 3

change in cell shape, interactions and/or location

Question 4

What happens in gastrulation

Answer 4

as you form the gut tube, the cells in the blastula invaginate
there’s a hollow ball of cells, and cells crawl along the inner surface ( green cells)

Question 5

What are the 3 concepts of cell morphogenesis

Answer 5

1. Cell internalization
   1.1 Ingression/delamination
   1.2 Invagination/involution
2. Elongation
   2.1 Convergent extension
   2.2 Cell division, Cell division, and cell matrix deposition
3. Fine repositioning of cells
   3.1 Migration of whole cells
   3.2 Migration of a cell extension

Question 6

ingression

Answer 6

individual cells detach from the outer cell layer and migrate in (this is an epithelial-to-mesenchymal transition)

Question 7

delamination

Answer 7

These cells form a new cell layer, the mesoderm

Question 8

How is tthe mesoderm formed ?

Answer 8

• Ingression: individual cells detach from the outer cell layer and migrate in (this is an epithelial-to-mesenchymal transition)
• Delamination: these cells form a new cell layer, the mesoderm

Question 9

How is the endoderm formed ?

Answer 9

Cell internalization by invagination/involution

• Attached cells in an epithelial cell sheet are pulled into the middle of the embryo while remaining attached (invagination)
• These cells curl in and grow (involution) to form the endoderm

Question 10

The direction of action of microtubules and actin

Answer 10

microtubules act vertically, actin contracts horizontally

Question 11

How does the neural tube form

Answer 11

invagination/involution

• Upstream developmental signals instruct specific cells to differentiate from ectoderm to neural plate cells
• Neural plate cells invaginate to form the neural tube
• Instructions include differential gene expression (e.g. different cadherins)

Question 12

Which of the following statements made by (imaginary) BIO230 students is
not true?
a) “Formation of the neural tube uses invagination, but formation of the gut tube does not.”
b) “Tissues with high cellular turnover typically also have molecular turnover.”
c) “Some cells do differentiate in adults.”
d) “Development occurs throughout all phases of life, including during
adulthood.”

Answer 12

a

Question 13

What are the ways in which elongation occurs ?

Answer 13

convergent extension
1. Cells converge or crawl together
2. Cells extend or form a line mass cell

migration
* Cells can move as individuals or as a group to form different shapes, called collective cell migration
* Chain-type migration involves fewer adherent cells
* Sheet-type migration involves more adherent cells

cell division, cell growth, or matrix deposition
These can lead to elongation/ directional cell growth if the processes are asymmetric

Question 14

How do plants grow by directional expansion

Answer 14

• Plant cells have a plant cell wall
• The cell wall is an extracellular matrix made of polysaccharides (sugars), rather than proteins
• One polysaccharide, cellulose, can be asymmetrically distributed in the plant cell wall
• Cellulose constricts plant cell expansion, forcing expansion in one direction leading to elongation

Question 15

What plays a key role in orienting cellulose microfibrils

Answer 15

microtubules

Question 16

Fine repositioning of cells

Answer 16

Cerebral cortex cells are repositioned by whole-cell migrations
* Whole cells migrate to the tip of the radial glial cell
* First-born neurons are in the deeper layer, last-born
neurons are in the outer layer

Axons are positioned by migration of cell extension
Attractants direct the extensions of the growth cone in a particular direction

Extracellular signals can polarize migration of a cell extension
* chemoattractants

• The exact receptors & attractants & signaling pathways will be different between a neutrophil and an axon
  growth cone, but the concepts will be similar

Question 17

Which morphogenesis process is correctly matched with the example developmental process?
a) Cell division & cell shape change – neural tube formation
b) Convergent extension – plant cell elongation
c) Ingression/delamination – cerebral cortex development
d) Invagination/involution – gastrulation

Answer 17

D