Lecture 10 - Body Plan II Flashcards
What are the 3 zones of the mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
Paraxial (segments plate) mesoderm
- thick column of mesoderm closest to and parallel with notochord
- becomes segmented into somites
Intermediate mesoderm
- narrow column of mesoderm lateral to the paraxial mesoderm
- gives rise to urogenital system
Lateral Plate Mesoderm
- thin plate of mesoderm lateral to intermediate mesoderm
- splits to form lining of body cavities and mesoderm of most internal organs as well as limbs
Mesoderm originates from ______, passes through _____ _____ as ____ cells, spreads laterally, and establishes a continuous layer between ectoderm and endoderm.
Epiblast
Primitive streak
Bottle
Somitomeres
Initial paired segments of mesenchyme that begin to develop along neural plate in paraxial mesoderm. New ones added caudally as primitive steak regresses. After 20 pairs form, the first pair of somites begins to form behind the 7th pair. The rest are gradually converted to somites. 11 pairs remain constant at caudal end of paraxial mesoderm.
Cells migrating through the primitive streak will form the __, __, and __ vertebrae.
Cells migrating through the tail bud will form the __ and __.
Clerical, thoracic, lumbar
Sacrum, coccyx
Somite development
1) epithelial stage
2) epithelialiomesenchymal transformation stage
3) separation of the myotonic
4) break up of epithelial dermatology into dermal fibroblasts
Somite Differentiation
Wavefront Mechanism
- ^ FGF-8 results in mitosis in mesenchymal cells
- ^retanoic acid anteriorly opposes FGF-8
- mess-2 is critical and expressed bc of balance btwn for-8 and retinoids acid
Segmentation Clock
- oscillating expression of notch pathway molecules est pattern for somite formation along a time line
- lunatic fringe concentrates at the future anterior border of a somite and c hairy concentrates at the posterior
- anterior cells express Eph A, posterior express Eph B
Dermomyotome
- dorsolateral portion
- Shh signaling from notochord and Wnt signaling from dorsal neural tube create balance causing myotome to commit to myogenic lineage
- FGF from myotome signals sclerotome to produce scleraxis which causes formation of syndetome (tendon precursor)
Sclerotomal Breakup
- breaks to ant and post portions
- posterior of one joins anterior of the next
- this creates a gap to allow nerves to grow out from the neural tube into epaxial musculature derived from the myotome
Intermediate Mesoderm
Future IM responds to BMP and activin; becomes IM and expresses Pax-2.
- IM is associated with formation of pronephros and mesonephros
- craniocaudal axis relies on Hox-4 and Hox-11 expression
What can you see in a 24 hour chick embryo?
Notochord, Somite, Intersomitic Furrows
Early heart-forming cells
- arise in epiblast
- migrate through primitive streak
- anterior PS: form outflow tract
- middle PS: form ventricles
- posterior PS: form atria
What results in commitment of cells to heart-forming pathway?
Inductive influence by endoderm
