L3- Cell Fate and Asymmetrical Division

Question 1

How do cells become different from their neighbours?

Answer 1

1. Cells are induced to become different by signals from other cells- induction.
2. Daughter cells are born different via asymmetric division.

Question 2

What is induction?

Answer 2

The process by which a signal from one cell or group of cells influences the development of one cell or group of cells.

Question 3

What is short range signalling (induction)?

Answer 3

Direct signalling from one cell to another causes its cell type to change. (may require cell-cell contact).

Question 4

What is long range signalling (induction)?

Answer 4

A gradient of signal from one cell induces multiple cell s fates according to the concentration of the signal when it reaches them.

Question 5

What are examples of induction?

Answer 5

1. Development of the eye. Optic vesicle induces ectoderm to differentiate into lens placode. Lens placode induces ectoderm to form cornea.
2. Development of the vulva in C. elegans relies on a diffusible signal (EGF molecules) and lateral inhibition.
3. Spemann organiser uses long-range signalling by BMP inhibitor proteins to give different mesoderm cell fates and induce formation of neural tissue from epidermis.

Question 6

What are the 3 mechanisms of induction?

Answer 6

1. Diffusion- secretion of a signalling molecule from one cell that will bind to a receptor on a neighbour.
2. Direct contact- receptors on cells directly bind to eachother.
3. Gap junction- direct contact via gap junctions.

Question 7

What is asymmetric cell division?

Answer 7

The process by which one cell divides to give two daughter cells with varying identities or fates.

Question 8

How does asymmetric cell division work?

Answer 8

It involves the segregation of cytoplasmic determinants in the progenitor cell and then to one or the other of the daughter cells. Each daughter cell adopts the developmental fate dictated by the determinants it inherits.

Question 9

Why is the mitotic spindle important in asymmetric division?

Answer 9

The orientation of the mitotic spindle must be aligned with the segregated determinants to ensure they are inherited by different daughters. If it is not coordinated then symmetric fates will occur due to even inheritance.

Question 10

What are examples of asymmetric division?

Answer 10

1. Neuroblasts in Drosophila divide asymmetrically to give another neuroblast and a smaller ganglion mother cell.
2. Asymmetric division in Drosophila sensory organs.
3. Asymmetric division in C. elegans to produce a large anterior AB cell and smaller posterior P cell.

Question 11

What are numb proteins?

Answer 11

Involved in the asymmetric division of Drosophila sensory organs (bristles).
Function by inhibiting signalling by the notch proteins as a cell surface receptor.
Inhibition of notch by numb proteins produces neural cell fates.