Somitogenesis

Question 1

Notch pathway?

Answer 1

Important for co-ordinating the segmentation of somites.

Question 2

What do somites give rise to?

Answer 2

The skeleton

Question 3

Somites?

Answer 3

Thry are made from non-segmented mesoderm.

Adjacent to midline tissues, neural tube/ notochord.

Developmental gradient along antero-posterior axis.

See AS31

Question 4

What happens to the primitive streak during development?

Answer 4

Shrinking

Node streak border (NSB) cells migrate.

AS32

Question 5

How are new somites recruited?

AS32/33

Answer 5

New pre-somitic mesoderm cells recruited from the primitive streak and later from the NSB.

As the primitive streak starts the shrink the Node streak border cells begin to migrate.

Progression of development- cells into somites at the head end of the pre-somitic mesoderm.

Question 6

What type of transition is the somite formation?

Answer 6

Mesenchymal to epithelial transition

Question 7

MET?

Answer 7

Mesenchymal–epithelial transition

reversible biological process that involves the transition from motile, multipolar or spindle-shaped mesenchymal cells to planar arrays of polarized cells called epithelia

Question 8

What happens with the primitive streak continues to regress?

Answer 8

Somites form from the paraxial mesoderm by budding off.

Compact and separate into discrete bodies.

Question 9

Clock-wavefront model?

Answer 9

Splitting event from paraxial mesoderm to somites.

Waves of developmental signals cause the periodic formation of new somites.

Question 10

When is somites formed?

Answer 10

As the notochord and neural tube forms.

Week 3

Question 11

What is the somite period of development

Answer 11

Day 20-30

Question 12

How are the somites specialised?

Answer 12

According to their location.

Segemental paraxial mesoderm, from which they are derived from, is itself, determined by its position along the anterior-posterior axis

Question 13

Chairyl?

AS34

Answer 13

Its expression initiates as a broad bond in the posterior PSM (presomatic mesoderm).

Moves anteriorly and reaches the anterior end of the PSM.

Question 14

Notch Pathway?

Answer 14

See additional sheet 35

Regulated by negative feedback

Question 15

Name the 3 clock genes that are expressed in the presomitic mesoderm?

Answer 15

Notch targets

Wnt targets

FGF targets

Question 16

FGF pathway?

Answer 16

AS36

Question 17

Wnt pathway?

Answer 17

AS37

Question 18

What happens when there is too much or little expression of the clock genes?

Answer 18

The segments are not distinct

Question 19

Border formation?

Answer 19

Border cells are specific.

Put them in a region that usually wouldnt be bordered-will now border.

Formed by activation of Notch activity.

Question 20

Notch1

Answer 20

Stimulats a segmenter

Question 21

What does the segmenter do?

Name of the segmenter?

Answer 21

L-fringe

Makes a border between cells

See AS38

Question 22

Why is the sequence of somite formation from the pre-somitic mesoderm autonomous?

Answer 22

Self-governed

As the tissue has information already to tell it what it should specalise to become

ie. even if you mix the somite 4 with the somite 10. The somite 4 will develop into the wrist even if its now located it a different location.

Question 23

Expression of Hox genes?

Answer 23

Provides the basis for A/P axis.

Common mechanisms underlying the development of all animals

Question 24

Co-linearity?

Answer 24

Correspendence between the order of the genes on the chromosome and their order of spatial and temporal expression along the A/P axis.

Question 25

What effect does Hox genes have on somites?

Answer 25

Specify somites as a whole based on their position along the A/P axis through specifying the pre-somitic mesoderm

Question 26

When do somites loss their plasticity?

Answer 26

The ability to form any kind of structure.

Retain plasticity until late somitic development

Question 27

Name the direction of the signals from the surrounding tissues govern somite differentiation

Answer 27

Ventralising

Lateralising

Dorsaling

Medialing

Question 28

What does the Wnt1 and 3a stimulate the production of what?

Answer 28

Skeletal muscles (back)

Question 29

What does the shh signal stimulate the production of?

Answer 29

Vetrebrate, ribs

Question 30

What does the Wnt1 and NT3 signal stimulate the production on?

Answer 30

Dermis

Question 31

What does the Wnt, BMP4, FGF5 signal stimulate the production of?

Answer 31

Skeletal muscles (Body)

Question 32

What does the Shh have a negative stimulation of?

Answer 32

BMP4

Question 33

Noggin has a negative signal on?

Answer 33

BMP

Question 34

Name the 5 process of somite formation?

Answer 34

1. Recruitment and maturation of precursor cells.
2. Periodicity driven by a molecular oscillator.
3. Border formation and epithelialisation.
4. Specification along the AP axis.
5. Differentation

Question 35

Recruitment and maturation of precursor cells?

Answer 35

From the primitive streak

Pool of embryonic stem cells.

Question 36

Periodicity driven by a molecular oscillator?

Answer 36

Notch and Wnt pathways are the principle component of the molecular clock

Question 37

Border formation and epithelialisation?

Answer 37

Mesenchymal-to-Epithelial transition

Induced by Notch activity

Question 38

Specification along the AP axis?

Answer 38

Early specification of AP identity in the pre-somitic mesoderm.

Expression of Hox genes provides the basis for AP axis specification.

Question 39

Differentiation?

Answer 39

Response to molecular signals from surrounding tissues.