Tissue Morphogenesis

Question 1

What are the key concepts in muticellular development?

Answer 1

1. Cell proliferation- increase in cell numbers via cell division
2. Cell differentiation - change in cell fate via cell signalling and differential genome expression
3. cell morphogenesis - change in cell shape, interactions, and/or location

Question 2

3 key tissue layers formed during gastrulation

Answer 2

Ectoderm → epidermis & nervous system
* Mesoderm → muscles, connective tissue, bones, blood, kidneys, etc
* Endoderm → gut, lungs, pancreas, liver, etc

Question 3

Morphogenesis =
generation of shape

Answer 3

1. Cell internalization
2. Elongation
3. Fine repositioning
   of cells

Question 4

Cell internalizatio

Answer 4

1. ingression/ delaminaiton
2. invagination/involution

Question 5

elongation

Answer 5

convergent extension
cell growth, division and cell matrix deposition

Question 6

fine repositioning of cells

Answer 6

1. migration of whole cells
2. migration of a cell extension

Question 7

ingression and delamination

Answer 7

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 8

invagination and involution

Answer 8

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 9

what is essential for invagination/involution

Answer 9

cell adhesion

Question 10

how does vertebral neural tube form

Answer 10

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

Question 11

convrgent extension

Answer 11

1. cells converge or crawl togetehr
2. cell extend or form a line

Question 12

cell migration

Answer 12

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

Question 13

what must be necessary for elongation to occur

Answer 13

cell division and growth and matrix deposition must be assymetric

Question 14

what grows by directional expansion

Answer 14

plant cells

Question 15

directional expansion in plant cells

Answer 15

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 16

what is plant cell deposition guided by

Answer 16

microtubules
Disorganized microtubules will disrupt plant cell elongation

Question 17

how are cerebral cortex cells repositioned

Answer 17

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

Question 18

how are axons positioned

Answer 18

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