Development III

Question 1

Describe the differences between preformation and epigenesis

Answer 1

Preformation is the idea that sex cells or fertilised egg already contain the organs and tissues that would later on grown in size during development

Epigenesis is the idea that organs and tissues are added progressively during development at increasing complexity overtime

Question 2

What are the 3 mechanisms we known for cell commitment ?

Answer 2

The 3 mechanisms of cell commitment are caused by
- Localised determinants
-Embryonic induction ( cell interactions )
- Morphogen ( gradients )

Question 3

Describe how localized determinants lead to specialised cells

Answer 3

Before cell division proteins in the fertilized egg cell are already segregated
Through divisions each cell will contain different amounts and types of proteins which will then determine what cell type they become
In summary: Assymetric divisions of cells lead to specialisation of cells

Question 4

Give an example of proteins which regulate the asymmetric division and cell polarity

Answer 4

PAR proteins regulate the asymmetric division and polarity of cells

Question 5

Give reasons as to why embryonic induction is believed to be true ( Mention sea urchin experiment and dissociation of animal cap and vegetal hemisphere )

Answer 5

• When the 4 daughter cells of sea urchin blastomeres were seperated they developed into 4 smaller larvae rather than 4 incomplete parts of 1 whole larvae
  – suggests that cell interactions reduce the potency of each cell

When the animal cap and vegetal hemisphere were seperated they developed on their own but no mesoderm were produced
- when reintroduced back together they then developed a mesoderm between them

Question 6

How did the xenopus assay cap experiment determine MIFs ( Mesoderm Inducing Factors )

Answer 6

The animal cap has been put in different cell cultures containing different proteins
- When the ectoderm elongates ( by convergent extention ) the mesoderm has been produced
- the protein added to that cell culture would then be a MIF

Question 7

What are the two families of MIFs we recognize ?

Answer 7

TGF-Beta family and the FGF family

Question 8

The neural tube has distict dorsal-ventral pattern of neural subtypes
- Describe how morphogen gradient arises this
( what morphogen is produced )

Answer 8

The notochord releases Shh ( Sonic hedgehog )
The induces the floor plate closely associated with the floorplate of the neural tube to produce Shh itself
The Shh diffuses through the neural tube and Shh concentration gradient is established
- higher concentration closest to the floorplate
- Different concentrations of Shh induces multiple cell fates