Lecture 10 Flashcards
Characterize location of each mesoderm.
- paraxial segmental plate mesoderm: thick column mesoderm closest to the notochord, becomes segmented into somites
- Intermediate mesoderm: narrow column lateral to paraxial mesoderm gives rise to urogenital system
- Lateral plate mesoderm: thin plate of mesoderm lateral to intermediate mesoderm, splits to form lining of body cavitities and mesoderm of most internal organs as well as limbs.
Distinguish between somitomeres and somites.
- somitomeres are initial paris of mesenchyme that develop along either site of neural plate in PARAXIAL mesoderm as primitive streak regresses
- after 20 pairs have formed the first pair of somites forms behind the 7th pair of somitomeres. (so the 8th transforms)
- Somites are dense blocks of mesoderm along the notochord and are discernable unlike somitomeres
In relationship to somitomeres at what position does the first pair of somites form?
- Somites pairs appear behind the 7th pair of somitomeres
- There are 11 pairs of somitomeres at caudal end
What is relationship of ephrin b, wnt-6, snail, and paraxis to somite formation?
- Ectoderm dorsal to somites expresses Wnt-6 wich causes paraxis to be expressed
- Paraxis plus decreasing snail leads to mesenchymal cell to epithelial cell conversion forming somitocoel (space btw somties)
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Relate Shh, noggin, Pax1, Pax9 to formation of sclerotome.
The notochord expresses Shh and Noggin which leads to the expression of Pax1 and Pax9 in the ventral part of the somite creating the sclerotome.
In wavefront step of somitogenesis what is the determination front?
- An increase in FGF-8 leads to mitosis in mesenchymal cells in posterior primitive streak and RA is more anterior and opposese FGF-8.
- A balance between RA and FGF-8 results in cessation of somitogenesis
- called determination becase of the balance between FGF-* and RA
What role does thte downregulation of snail play in somatogenesis?
Downregulation of snail plus paraxis leads to mesenchymal cell conversion to epithelial cells.
In the segmentation clock of somitogenesis describe hte role of ephrins in maintaining intersomitic spaces.
- Posterior border anterior somite express ephine B ligand and anterior border express Eph A receptor resulting in fissure between somites.
- Lunatic fringe is concentrated at future anterior border of somite and C-hairy is concentrated at posterior border at each critical location to divide adjacent somites.
- Notch pathway!
Describe formation of dermomyotome and factors and paths involved.
- Shh signaling from the notochord and Wnt from the dorsal neural tube balances out causing myotome portion to commit to myogenic lineage.
- Noggin inhibits BMP-4 that would normally inhibit myogenesis. BMP4 produces by lateral plate
- FGF from myotome signals sclerotome to produce sceraxis causing anterior and posterior borders of each somite to form syndetome which is precursor of tendons.
Describe separation of dermomyotome into myotome and dermatome and the factors involved.
- The dermomyotome expresses its own genes, Pax3, Pax7 and Paraxis. Then mesenchymal cells from the dorsomedial and ventrolateral borders of the dermomyotome form a separate layer called the myotome beneath the somitic epithelium. The epithelium is called the dermatome.
Wnt in dorsal neural tube transform dorsal somite into dermomyotome and that expresses Pax3, Pax7 and paraxis.
Leading to separation of dermomyotome in dorsal dermotome and ventral myotome.
List derivatives from final subdivision of somites.
- dorsal half of epithielial somite becomes dermomyotome.
- Myotome is beneath the epithelium and comes from mesenchymal cells of the dorsomedial and ventrolateral borders
- the somitic epithelium remaining is called the dermatome
List factors involved in formation of intermediate mesoderm and list derivitives.
- Arises as a response of early mesoderm to BMP which is secreted by the lateral ectoderm and activin secreted from the paraxial mesoderm. The response is to express Pax-2
Differentiate between intraembryonic coelom and extraembryonic coelom.
- Folding of the coelomic vesicles within lateral plate mesoderm into the coelomic cavity separates intra from extra.
Distinguish between somatic and splanchnic mesoderm.
Both divide the lateral plate mesoderm into two layers:
- Dorsal layer closely associated with ectoderm is called somoatic mesoderm. Makes up the lateral and ventral body wall of the Coelom, and also mesenchyme of limb buds.
- The ventral layer is the splanchnic mesoderm and is closely associated with the endoderm and specified by the TF Foxf-1. Forms mesentery and wall of GI
Describe formation of lateral plate mesoderm and distinguish betweeen somatopleure and splanchnopleure.
- Somatopleure is the combonation of somatic mesoderm and ectoderm
- Splanchnopleure is the combinded endoderm and splanchnic mesoderm.
- BMP-4 induces molecular and cellular properties of Lateral plate mesoderm
