Lecture 10: Establishment Of Body Plan 2 Flashcards Preview

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Flashcards in Lecture 10: Establishment Of Body Plan 2 Deck (15)
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1

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

2

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

3

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

4

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

5

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

6

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.

7

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.

8

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

9

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

10

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

11

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)

12

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.

13

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

14

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

15

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