Mesoderm differentiation and Somitogenesis

Question 1

What are 4 types of mesoderm?

Answer 1

Axial, paraxial, lateral plate, intermediate

Question 2

What does the axial mesoderm become?

Answer 2

Notochord

Question 3

What does the paraxial mesoderm become?

Answer 3

Somites and head

Question 4

Which type of mesoderm splits into two plates as development progresses? What are they?

Answer 4

Lateral plate mesoderm splits into the somatic mesoderm and the splanchic mesoderm

Question 5

What does the lateral plate mesoderm become?

Answer 5

Skeleton, muscle, circulatory system

Question 6

What does the somatic mesoderm become?

Answer 6

Muscles

Question 7

What does the splanchic mesoderm become?

Answer 7

Connective tissues of internal organs

Question 8

What does the intermediate mesoderm become?

Answer 8

Kidneys and gonads

Question 9

How does the anterior-posterior axis in elongate in vertebrates?

Answer 9

Proliferation of neuromesodermal progenitor cells in the posterior progenitor zone

Question 10

How does the notochord elongate?

Answer 10

The notochord cells inflate their vacuole and spread out

Question 11

What are the 3 things somites differentiate into?

Answer 11

Sclerotome, myotome, dermatome

Question 12

What does the sclerotome become?

Answer 12

Vertebrae and rib cage

Question 13

What does the myotome become?

Answer 13

Back/rib cage and body wall muscles

Question 14

What does the dermatome become?

Answer 14

Skeletal muscles and some dermis

Question 15

What is somitogenesis?

Answer 15

The anterior-posterior division of the paraxial mesoderm that separates it into distinct units

Question 16

What are the 5 steps in somitogenesis?

Answer 16

1. Establish molecular periodicity
2. Fissure formation between 2 cell populations
3. Epithelialization
4. Specification
5. Differentiation

Question 17

What are the two steps that establish periodicity in the presomitic mesoderm?

Answer 17

The wave and the clock

Question 18

What 3 signals are involved in the wave to cause periodicity in the somites?

Answer 18

Retinoic acid, FGF, and Mesp

Question 19

Where is retinoic acid expressed in the somites?

Answer 19

Anterior

Question 20

Where is FGF expressed in somites?

Answer 20

Posterior

Question 21

Where is Mesp expressed in the somites?

Answer 21

Where RA and FGF are both absent

Question 22

What does Mesp do?

Answer 22

Activates transcription of Eph A4 - an ephrin receptor

Question 23

How is the fissure between somites formed?

Answer 23

Cells with EphA4 are localized in the anterior end of the somite, and are repelled by cells with ephrin B2. The EphA4 cells are also repelled by the posterior end of the next somite and causes a fissure between them

Question 24

What regulates the pattern of Mesp expression?

Answer 24

Delta-Notch signalling. Isolates Mesp to the anterior end of the somite

Question 25

Why is Mesp not expressed in the posterior end of the somites?

Answer 25

Those cells are receiving FGF signalling which prevents Notch from responding to Delta. Cells get pushed away from the FGF signal towards the anterior end and then Notch can respond to Delta

Question 26

What are the two transcription factor activated by Notch in the anterior somite?

Answer 26

Mesp and Lunatic Fringe (Lnfg)

Question 27

What does Lunatic Fringe do?

Answer 27

Inhibits Notch

Question 28

What is causing the clock that establishes periodicity?

Answer 28

Self inhibition by Notch

Question 29

What determines the number of somites?

Answer 29

The rate at which periodicity occurs

Question 30

Why do snakes have more somite divisions?

Answer 30

They have more areas of Lunatic Fringe activity, which creates more somite divisions, but each somite is smaller