General principles of development

Question 1

What 3 things make drosphila melanogaster a good model for development?

Answer 1

1. Rapid life cycle
2. Small csize
3. Genetically tractable

Question 2

Describe the process of a sperm fusing with an egg

Answer 2

1) Upon contact sperm releases acrosome containing hydrolytic enzymes which break down the zona pellucida
2) Plasma membrane of sperm fuses with that of the egg
3) Initiation of cortical reaction to prevent polyspermy

Question 3

What is the name of the 16 cell phase and the 58 cell phase?

Answer 3

16 cell - morula

58 cell - blastocyst (has a lumen, can embed in the uterus wall after hatching from the ‘zona pellucida’)

Question 4

Describe Carnegie stage 6 (13-14 days)

Answer 4

• Is a bilayer embreyonic disc (epiblast and hypoblast)

- Had an amneotic cavity and yolk sac which are all surrounded by te chronic cavity

Question 5

What is gastrulation?

Answer 5

The movement of cells into the blastula (which becomes the gastrula) to form the mesoderm and endoderm, remainder becomes the ectoderm

Question 6

What happens in Carnegie stage 7?

Answer 6

Epiblast cells gastrulate to give mesoderm. Notochord tube forms under ectoderm. Disc folds ventrally enclosing some yolk.

Question 7

What happens in Carnegie stage 8?

Answer 7

The amniotic sac is torn open. Brain folds, neural groove, presomitic mesoderm established, primitive node, primitive streak

Question 8

What is established in Carnegie stage 6-8?

Answer 8

Axes and the three germ layers

Question 9

What are the 3 germ layers?

Answer 9

1. Ectoderm - epidermis and neurons
2. Mesoderm - muscle, tubule cells (kidney), red blood cells
3. Endoderm - lung cells, thyroid cells and pancreatic cells

Question 10

Describe the process of neurolation in a human embreyo

Answer 10

• Called neurula
• Neutral plate folds up around the notochord to form a neural fold joining to form the epidermis and neural tube
• Formation of neural crest

Question 11

Describe the process of somitogenesis in a human embreyo

Answer 11

• Formation of somites (muscles + skeleton)

- Paired balls of mesoderm form the strips of paraxial mesoderm which flank the notochord

Question 12

What do the branchial arches and placodes go on to form?

Answer 12

Build face, branchial arches, inner ear, jaw and outer nose

Question 13

What are the 3 essential steps of development?

Answer 13

1. Regional specification
2. Morphogenesis (generation of from)
3. Cell differentiation

Question 14

What is polarity?

Answer 14

regional difference in state of commitment

Question 15

What is a morphogen?

Answer 15

A substance whose variable levels cause

differential responses downstream

Question 16

How does bicoid work in drosphila melanogaster?

Answer 16

Bicoid mRNA codes for the formation of a head and thorax, and is located to the anterior pole and is translated into protein which spreads towards the posterior forming an anterior-posterior gradient.

Question 17

What other effect can levels of bcd mRNA have?

Answer 17

Can shift the position of where downstream targets are activated due to various thresholds for multiple downstream genes

Question 18

How do maternal bicoid levels affect the expression of pair rule genes?

Answer 18

As they activate/repress various downstream gap genes which in turn regulate the pair-rule genes which in turn define boundaries

Question 19

How is positional information encoded in drosphila?

Answer 19

Hox code determines differentiation pathways

Question 20

Define compartments

Answer 20

A multicellular region within which the progeny of every cell remain confined

Question 21

What is an embreyonic field?

Answer 21

An area of embryo/tissue within which a certain process occurs

Question 22

Why is xenopus laevis a good model?

Answer 22

As its large eggs are amenable to ‘cut-and-paste embreyology’

Question 23

What are the ‘animal’ and ‘vegetal’ poles of an egg?

Answer 23

Defined before fertilization.
Animal: where sperm enters, more ‘animated’ cell divisions
Vegetal: Rich yolk with fewer divisions

Question 24

What are the stages of xenopus laevis embreyogenesis?

Answer 24

1. Fertilisation
2. Cleavage (division without growth)
3. Formation of gastrula with 3 germ layers

Question 25

What is induction?

Answer 25

• The process by which one embreyonic region interacts with a second embreyonic region to influence the second region’s differentiation or behavior.
• Can come from other cells or the environment
• Signal can be ‘instructive/directive’ or ‘permissive’

Question 26

What are the 3 methods of induction?

Answer 26

1. Diffusion - signal form one cell interacts with a receptor on a target cell
2. Direct contact - interaction of transmembrane proteins
3. Gap junction - movement of signals between connected cells

Question 27

What is specification?

Answer 27

If a tissue/cell explant develops autonomously into a particular structure after isolation from the embreyo

Question 28

What is fate?

Answer 28

The final state of cells of tissue during normal development
Change over time

Question 29

What 3 methods can be used to create a fate map?

Answer 29

1. Use dyes such as Nile Blue/fluorescently labelled dextrans
2. Transplantation of pigmented into albino tissue
3. Fluorescently tagged protein

Question 30

What is determination?

Answer 30

Progressive restriction in developmental potential of different cell types

Question 31

What is acquisition of commitment via lineage?

Answer 31

When the state of commitment of a cell is inherited from its determined parent cell

Question 32

What is mosaic is?

Answer 32

When the map of specified regions (determined independently of each other) exactly match the fate map

Question 33

What is regulation?

Answer 33

When the specification of isolated parts does not correspond to the fate map

Question 34

What is a stereotypical cell lineage?

Answer 34

When we can name each cell and see exactly what it came from and what it becomes