Lecture 10: Establishment Of Body Plan 2 Flashcards
Mesoderm originates from —————-, passes through ————————- as —————— and spreads laterally and establishes layer btwn ectoderm and endoderm
A. Endoblast, notocord, as somite
B. Epiblast, notocord, primitive streak
C. Epiblast, primitive streak, bottle cell
D. Endoblast, primitive streak, blood island
Ans: C mesoderm originates from epiblast, passes through primitive streak as bottle cells, spreads laterally, and establishes a continuous layer between ectoderm and endoderm
Three zones of mesoderm are: A. Segmental, epidermis and endoderm B. Superficial, intermediate and deep C. Segmental, uniform and differentiated D. Paraxial, intermediate and lateral
The four options
Ans: D. Paraxial, intermediate and lateral
Thick column of mesoderm closest to and parallel with the notochord A. Paraxial (segmental plate) mesoderm B. Intermediate mesoderm C. Lateral plate mesoderm
Ans: A
Paraxial (segmental plate) mesoderm: • Thick column of mesoderm closest to & parallel with the 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 &mesoderm of most internal organs as well as limbs
Which is not true of somitomeres?
A. Somitomeres are initial pairs of segments of mesenchyme that begin to develop along and on either side of the neural plate in the paraxial mesoderm
B. Dense blocks of mesoderm that form along the
notochord
C. After 20 pairs of somitomeres have formed , the first pair of
somites forms behind (caudal to) the 7th pair of somitomeres at the expense of the eighth pair of somitomeres.
D. New somitomeres are added caudally as the primitive streak regresses and pairs of somites are formed, pairs of somitomeres are also formed at the anterior end of the primitive node
Ans B• Somitomeres are initial pairs of segments of mesenchyme (barely discernable as segments) that begin to develop along and on either side of the neural plate in the paraxial mesoderm.
• New somitomeres are added caudally as the primitive streak regresses.
• After 20 pairs of somitomeres have formed (about day 20), the 1st pair of somites forms behind (caudal to) the 7th pair of somitomeres at the expense of the 8th pair of somitomeres.
• Somites are more dense blocks of mesoderm that form along the
notochord.
• In a caudal direction, a pair of somitomeres is transformed into a pair of somites every few hours.
• As pairs of somites are formed, pairs of somitomeres are also formed at the anterior end of the primitive node
Cells migrating from the tail bud will form
A. Sacrum and coccyx
B. Lumbar vertebrae
C. Cervical vertebrae and thoracic vertebrae
D. Lumbar vertebrae and sacrum
Ans: A
Cells migrating through the primitive streak will form the cervical,
thoracic, and lumbar vertebrae.
• Cells migrating from the tail bud will form the sacrum and coccyx
At the critical location that divide adjacent somite ——- will become concentrated on the future anterior border. A. Lunatic fringe B. C- hairy D. Eph A E. Eph B
Ans: A
At each critical location that will serve to divide adjacent somites, lunatic fringe will become 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 of a somite express Eph A (receptor) and cells of the posterior border of the anterior somite will express Eph B (ligand), resulting in a fissure between the two adjacent somites.
Wavefront is also referred to as the determination front because there is a balance between ————and ——— that results in cellular determination toward somitogenesis. A. Mesp -2 B. FGF 6 & thyroxine C. Mesp-2 and retinoic acid D. FGF-8 and Retinoic acid
Ans: D
Wavefront mechanism: • ↑[FGF-8] → mitosis in mesenchymal cells in posterior primiHve streak
• ↑[retinoic acid] more anteriorly opposes action of FGF-8.
• Note balance btwn the opposing gradients of retinoic acid and FGF-8 which results in a cessation of somitogenesis.
• Note that the wavefront is also referred to as the determination front b/c there is a balance btwn FGF-8 and retinoic acid that results in cellular determination toward somitogenesis.
• Mesp-2 is important at this critical decision moment and is expressed b/c of the specific balance between FGF-8 and retinoic acid concentrations.
Shh and Noggin are signaling molecules that active these genes in the notochord A. Snail, paraxis B. Pax 1, 9 C. Wnt D. Pax 3, 7
Ans: B Steps in Somite Differentiation
• Ectoderm dorsal to somites → Wnt-6 (SM)→ Paraxis (TF) in somite.
• Paraxis + ↓Snail (G) → mesenchymal cell to epithelial cell conversion.
• Formation of somitocoel.
• Notochord → Shh (SM) + noggin (SM) → Pax1 + Pax-9 (G)in ventral part of somite = sclerotome.
• Wnt genes in dorsal neural tube → transformation of dorsal half of somite into dermomyotome.
• Dermomyotome → expression of (G) Pax3, Pax7, paraxis → separation of dermomyotome into dorsal dermotome and ventral myotome.
SM = signaling molecule; TF = transcription factor; G-genes
Organization of a somite in as a dermomyotome follows this sequence:
A. Shh and Wnt -> noggin inhibiting BMP-4-> BMP-4 suppressor myogenesis-> FGF -> scleraxis-> syndertome ->tendons
B. BMP-4 suppressor myogenesis -> Shh and Wnt -> noggin inhibiting BMP-4-> FGF -> scleraxis-> syndertome ->tendons
C. Tendons -> sceleraxis -> syndertome-> BMP-4 suppressor myogenesis -> Shh and Wnt -> noggin inhibiting BMP-4-> FGF
D. noggin inhibiting BMP-4-> BMP-4 suppressor myogenesis -> Shh and Wnt -> FGF -> scleraxis-> syndertome ->tendons
Ans: A
Organization of a somite (Refer to Figure 6.12):
• Dermomyotome: • This is the dorso-lateral part of a somite.
• Shh signaling from the notochord and Wnt signaling from the dorsal neural tube create a balance that causes the myotome portion to commit to the myogenic lineage. • Noggin inhibits BMP-4, which would normally inhibit myogenesis.
• BMP-4 produced by the lateral plate suppresses myogenesis in the ventrolateral dermomyotome and stimulates cells from this area to migrate from the somite into the limb bud.
• FGF from the myotome signals the sclerotome to produce scleraxis, which causes the anterior and posterior borders of the each somite to form the syndetome which is the precuror of tendons.
All SM, scleraxis- TF
Intermediate mesoderm is associated with the formation of the
A. Precardia and later heart
B. pronephros and later mesonephro
C. Prehepatic liver and later liver
D. Early reproductive structure and later mature reproductive structure
Ans: B
Intermediate mesoderm is associated with the formation of the pronephros and, later, the mesonephro
Future intermediate mesoderm responds to which two signaling molecules A. FGF and retinoic acid B. TGF and PAX- 2 C. PAX 3, 9 D BMP and Activin
Ans: D
The future intermediate mesoderm responds to BMP (SM)(from lateral ectoderm) and activin (SM) (from paraxial mesoderm) and becomes intermediate mesoderm and expresses Pax-2 (TF)
NOTE: Cranial and caudal extent of the intermediate mesoderm is dependent on expression of Hox-4 through Hox-11 (genes)
Early heart forming cells arise in ——- and are formed due to the ——- influence by endoderm on cells A. Ectoderm, differentiation B. Epiblast, replication C. Epiblast, inductive D. Ectoderm, inductive
Ans: C
Early heart-forming cells: • Arise in epiblast Inductive influence by endoderm resulting in commitment of these cells to the heart-forming pathway.
Cells migrating through anterior primitive streak form A. Heart B. Outflow tract C. Ventricles D. Atria
Ans: B
Migrate through primitive streak:
• Cells migrating through anterior primitive streak: • Form outflow tract
• Cells migrating through middle of primitive streak: • Form ventricles
• Cells entering streak most posteriorly: • Form atria
Expression of genes by these cells to form transcription factors necessary for early heart formation. A. BMP and FGF B. FGF and retinoic acid C. PAX and Hox -6 D. Nkx2-5, MEF2, GATA4
Ans: D
Anterior Visceral
BMPs and FGFs Endoderm - act on by BMP and FGF - form cardiac crescent - Tf Nkx2-5, MEF2, GATA4 - necessary of early heart development
Each tube of the cardiogenic mesoderm consists of inner and outer later. What will they form? A. Cardiac jelly B. Proepicardial primordium C. Outer-myocardium, inner-endocardium D. Inner -Aorta and outer -venae cava
Ans: C
Early Heart Formation
• Cardiac Tubes: • Bilaterally paired tubes that form from the cardiogenic mesoderm:
• Fuse beneath foregut to form single tube.
• Each tube consists of an outer and an inner layer: • Outer layer will form myocardium.
• Inner layer will form endocardium.
• Cardiac jelly forms between the two layers: • Specialized extracellular matrix
• Proepicardial primordium: • Source of pericardium and myocardial fibroblasts
