Lecture 8

Question 1

What are morphogens?
What do they form and encode

Answer 1

Signalling molecules that form gradients and encode spatial information to direct cell fate.

Question 2

What are the stages of early vertebrate development?

Answer 2

Cleavage blastula

Question 3

What characterises cleavage - what happens with cell division and cell size?

Answer 3

Rapid synchronous cell division with no growth and reduction in cell size.

Question 4

What happens with cell division and what forms during the blastula stage?

Answer 4

Cell division becomes asynchronous and a fluid-filled cavity (blastocoel) forms.

Question 5

What is special about early blastula cells?

Answer 5

Some early cell specialisation begins.

Question 6

What are the animal and vegetal poles?

Answer 6

Animal pole: less yolk active division; Vegetal pole: yolk-rich

Question 7

What are the three germ layers formed during development?

Answer 7

Ectoderm mesoderm

Question 8

What forms from ectoderm?

Answer 8

Epidermis and central nervous system.

Question 9

What forms from mesoderm?

Answer 9

Notochord dermis

Question 10

What forms from endoderm?

Answer 10

Gut liver

Question 11

What happens during gastrulation with cells?

Answer 11

Major cell movements establish the three germ layers.

Question 12

What is the dorsal lip of the blastopore?

Answer 12

A key organiser region initiating gastrulation movements

Question 13

What body axes are established during gastrulation?

Answer 13

Dorsal-ventral and anterior-posterior axes.

Question 14

What is neurulation?

Answer 14

Formation of neural tissue and the neural tube.

Question 15

What is the tailbud stage?

Answer 15

Phylotypic stage and they have features similar to vertebrate embryos.

Question 16

What are key vertebrate embryo features?

Answer 16

Dorsal nerve cord segmented muscle

Question 17

Why is Xenopus laevis a good model organism?

Answer 17

Rapid development external embryos

Question 18

What is a morphogen gradient?

Answer 18

A concentration gradient of a signalling molecule that gives cells positional information.

Question 19

How do genes in cells respond to morphogen gradients?

Answer 19

They activate different gene programs based on threshold concentrations.

Question 20

What is the French Flag model?

Answer 20

A model where cells adopt different fates based on morphogen concentration thresholds.

Question 21

What is positional information?

Answer 21

Information cells use to determine their location relative to a signal source.

Question 22

What is the marginal zone?

Answer 22

The equatorial region of the embryo where mesoderm forms.

Question 23

What happens to early vs late blastula marginal zone explants?

Answer 23

Early: form epidermis; Late: form mesoderm indicating signalling changes over time.

Question 24

What induces mesoderm formation?

Answer 24

Signals from the vegetal pole.

Question 25

What is the source of mesoderm in Xenopus?

Answer 25

Animal cap cells induced by vegetal signals not vegetal cells themselves.

Question 26

What did lineage tracing show about mesoderm origin?

Answer 26

All mesoderm derives from animal cap cells.

Question 27

What are DV and VV regions?

Answer 27

Dorsovegetal induces dorsal mesoderm; ventrovegetal induces ventral mesoderm.

Question 28

What tissues arise from dorsal mesoderm?

Answer 28

Notochord and some skeletal muscle.

Question 29

What tissues arise from ventral mesoderm?

Answer 29

Blood and smooth muscle.

Question 30

What limitation was observed in DV and VV experiments?

Answer 30

They do not produce the full range of mesoderm tissues.

Question 31

What additional patterning is required?

Answer 31

Dorsal-ventral axis patterning.

Question 32

What is the three-signal model?

Answer 32

A model explaining mesoderm induction and patterning via three sequential signals.

Question 33

What are the three signals in the three-signal model?

Answer 33

Vegetal signal induces mesoderm dorsal signal forms dorsal mesoderm

Question 34

What is the DMZ?

Answer 34

Dorsal marginal zone a source of patterning signals.

Question 35

What signalling pathway is key for mesoderm formation?

Answer 35

TGF-beta signalling.

Question 36

What are TGF-beta ligands?

Answer 36

dimeric proteins that are secreted each with roles in development.

Question 37

How do TGF-beta signals get transduced?

Answer 37

Through serine/threonine kinase receptors activating SMAD proteins.

Question 38

What do SMAD proteins do?

Answer 38

Enter the nucleus and regulate gene transcription.

Question 39

What molecules act as morphogens in mesoderm formation?

Answer 39

Activin and nodal.

Question 40

What is nodal expression pattern?

Answer 40

A gradient with high dorsal and low ventral levels.

Question 41

What does nodal function act as and what does it control?

Answer 41

Acts as a morphogen controlling mesoderm patterning.

Question 42

What experiment showed activin-like signals are required?

Answer 42

Dominant-negative activin receptor blocked signalling and prevented mesoderm formation.

Question 43

What is a dominant-negative receptor?

Answer 43

A mutant receptor that blocks signalling by dimerising with normal receptors.

Question 44

What happens when nodal or activin signalling is blocked?

Answer 44

Embryos fail to form mesoderm.

Question 45

What is Brachyury?

Answer 45

An early mesoderm transcription factor used as a marker.

Question 46

What is the role of signalling in development overall?

Answer 46

It controls cell fate decisions and differentiation.

Question 47

What happens after mesoderm induction?

Answer 47

Cells activate transcription factors and differentiate into specialised tissues.