Mesoderm development - Lecture 15

Question 1

What are the subdivision or zones of mesoderm

Answer 1

Paraaxial (segmental) mesoderm

Intermediate mesoderm

Lateral plate mesoderm

Question 2

Paraxial

Answer 2

Thick column of mesoderm closest to and parallel with the notochord

Becomes segments into somites

Question 3

Intermediate

Answer 3

Norrow column of mesoderm, lateral to the paraaxial mesoderm

Urogenital system

Question 4

Lateral mesoderm

Answer 4

Thin plate of mesoderm lateral to intermediate mesoderm

Splits to form lining of body cavities and mesoderm of most internal organs and the limbs

Question 5

Somitomeres vs Somites

Answer 5

Somitomere’s are pre-somites, initial pairs of segmented mesenchyme on either side of the neural plate

Add caudally as primitive streak regresses and embryo elongates

First pair of somites forms from 8th pair of somitomeres and somitomeres are transformed into somites seqentially and in the caudal direction.

As somites are popping up so are new pairs of somitomeres

Question 6

what pair of somitomeres is the first somite formed from?

Answer 6

The 8th pair

Question 7

What factors are important for mesechyme conversion to somites?

Answer 7

Paraxial mesoderm - somites

Wnt-6 - stimiulates production of paraxis
Paraxis -stimulation by wnt-6: convert mesechyme cells to epithelial
Snail - downregulated
ephrin B - creates gap through the somite and keeps the cells from mixing

Question 8

Which TF cause induction of sclerotome? And where in the somite?

Answer 8

Portion of notochord releases shh and noggin which releases/influences release of Pax1 and Pax9 in the ventral portion of the somite.

Question 9

What’s the wavefront step of somitogenesis?

Answer 9

Determination front where FGF-8 is on the posterior end of the primitive streak and retinoic acid more anteriorly.

Retinoic acid opposes FGF-8

Determination front is the balance between the two factors that leads to somite differenciation

Mesp-2 is expressed because of the determination front

Question 10

Dermomyotome

Answer 10

Wnt genes in the doral neural tube leads to the transformation of the dorsal half of the somite in dermomyotome

Question 11

What does dermomyotome seperate into and how?

Answer 11

In dorsal dermotome and ventral myotome

By expression of Pax3 and Pax7 and paraxis

Myotome commitance is by shh and wnt, with noggin inhbiting BMP-4.

BMP-4 suppresses myogenesis and in the ventrolateral dermomytome causes cells to migrate to the limb bud

Myotome signals sclerotome with scleraxis to induce syndetome (tendons)

Question 12

Intermediate mesoderm

Answer 12

Responds to BMP (lateral ectoderm) and activin (from paraxial mesoderm)

Intermediate mesoderm expresses pax-2
- associated wit formation of pronephors and then mesonephros

Cranial and caudal end dependent on expression of Hox4 and Hox11

Urogenital system

Question 13

Somatic vs splanchnic mesoderm

Answer 13

Layers of lateral plate mesoderm

Somatic - dorsal layer

Sphlanchnic - ventral layer - Foxf-1

Lateral plate formation induced by BMP4

Question 14

Difference between somatepleure and splanchnopleure

Answer 14

Somatopleure - somatic mesoderm + ectoderm

Splanchnopleure - splanchnic mesoderm and endoderm

Question 15

What is the cardiac cresent? What induces it;s formation?

Answer 15

Cardiac mesoderm,

Induced by BMPs and FGFs (from anterior viseral endoderm)

Question 16

Describe the early formation of the heart

Answer 16

Early heart forming cells arise in the epiblast and migrate through the primitive streak

Anterior - outflow tract
Middle - ventricles
Posteriorly - atria

BMP and FGF help form cardiac cresent - which is cardiac mesoderm

Then cardiac tubes form and fuse, each tube with an outer and inner layer
Outer- myocardium
Inner- endocardium

Cardiac jelly- specializedextracellular matrix between the two layer

Percarium forms from proepicardial primordium

Question 17

What genes are important in early heart formation?

Answer 17

Nkx2-5
MEF2
GATA4

Question 18

What is the secondary heart field?

Answer 18

Just below the cardiac cresent

Forms the outflow tract and someof the right ventricle

Question 19

What are the derivatives of the cardiogenic mesodermal cells?

Answer 19

Form the left ventricle and most of the atria