Embryology Lecture 10 Establishment of Body Plan II Flashcards
What are the three zones of the mesoderm?
Paraxial mesoderm
Intermediate Mesoderm
Lateral Plate mesoderm
What is described by a thick column of mesoderms, closest to and parallel with the notochord, and becomes segmented into somites?
Paraxial Mesoderm
What is described by a narrow column of mesoderm, lateral to the paraxial mesoderm, and gives rise to urogential system?
Intermediate mesoderm
What is described by a thing plate of mesoderm, lateral to intermediate mesoderm, splits to form the lining of body cavities and mesoderm of most internal organs as well as limbs?
Lateral plate mesoderm
Where do the somitomeres begin to develop and where are they added?
Develop in the paraxial mesoderm and new ones are added caudally
What event happens simultaneously as somites are being created?
Creation of new somitomeres at the anterior end of the primitive node (primitive streak: caudal end)
How many pairs of somitomeres are kept constant at the caudal end of the paraxial mesoderm?
11 pairs (Possible 12)
Which vertebrae are made from the cells migrating through the primitive streak?
Cervical, thoracic, and lumbar vertebrae
At what point does the somitomere become a somite?
At the 7th somitomere at the expense of the 8th
Cells migrating from the tail bud will form ____
The sacrum and coccyx
What are the 4 steps of somite history and organization?
- Epithelial Stage
- Epitheliomesenchymal Transformation stage
- Separation of the myotome
- Breakup of epithelial dermatome into dermal fibroblasts
What is happening during the epithelial stage of somite organization?
Cells are bunched together
What is happening during the epitheliomesenchyal transformation stage of somite organization?
Some of the cells lose their binding to each other
They become more mobile and diffuse out
What happens during the separation of the myotome during somite organization?
Split up into three regions
Dermatome, myotome, and sclerotome
What signaling balance causes myotome portion to commit to the myogenic lineage?
Shh from the notochord and Wnt from the dorsal tube
What is the function of BMP-4 and what inhibits it?
Stimulates somites to migrate to the limb bud
Inhibited by Noggin
What signaling molecule from the myotome tells the sclerotome to produce scleraxis?
FGF
What is the purpose of scleraxis
Causes the anterior and posterior border of somties to form the syndetome (The precursor of tendons)
What creates gaps that allow nerves to grow in the neural tube?
Sclerotomal break up
It breaks up into an anterior and posterior portion
In sclerotomal breakup, what portions fuse?
The posterior portion fuses with the adjacent anterior portion
What model of somite differentiation is described below?
Be able to pick out the defining characteristics.
-Expressed along a timeline: 90 minutes/somite
-At each critical location that will serve to divide adjacent somites, lunatic fringe will become more concentrated at the future anterior border of a somite and c-hairy will be concentrated at the future posterior border of a somite
-cells at the anterior border will express Eph A (receptor)
-cells at the posterior border will express Eph B (ligand)
(These two will result in a fissure between the two adjacent somites)
Segmental Clock model
Refer to fig. 6.9
What model of somite differentiation is described below?
Be able to pick out the defining characteristics.
- There is an increase in [FGF-8] that leads to mitosis in the mesenchymal cells in posterior PRIMITIVE STREAK
- Increase in [RETINOIC ACID] more anteriorly as opposed to FGF-8 (which opposes mitosis)
- A balance becomes of the two which leads to a determination front. (this then leads to differentiation)
- Mesp-2 is expressed because of the balance
Wavefront Mechanism
Retinoic acid opposes what in the wavefront mechanism of somite differentiation?
FGF-8 which leads to the inhibition of mitosis
What is cessation of somitogenesis?
A balance between FGF-8 and Retinoic Acid in the wavefront model of somite differentiation
