Axes specification Flashcards

1
Q

What is the essential difference between basics of axis specification between anamniotes and amniotes?

A

anamniotes: contribution of maternal determinants
amniotes: interplay between embryonic and extraembryonic tissues

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2
Q

In xenopus: how does the organizer arise (what predetermines where the future dorsal site will form)?

A
  1. oocyte polarization along animal-vegetal axis (localization of maternal determinants)
  2. sperm entry site defines microtubule polymerization
  3. maternal determinants are transported along these microtubules to the future dorsal site
  4. B-catenin on dorsal site
    • > high Nodal(-related) protein
    • > low BMP at the site of organizer; high Chordin, Noggin, Folistatin
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3
Q

What do cells of the dorsal blastopore lip become?

Which characteristic transcription factor is present there?

A

DBL -> dorsal mesoderm

Chordin

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4
Q

What are the major functions of the organizer?

A
  • initiation of the gastrulation movements
  • generation of a self-regulation morphogen along DV
  • dorsalisation
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5
Q

What is dorsalisation?

A

organizer (DBL) -> dorsal mesoderm
dorsal mesoderm -> prechordal plate, notochord
also:
- mesoderm next to it becomes paraxial mesoderm (later: somites)
- ectoderm next to it forms neural tube

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6
Q

On which site along DV axis is BMP high?

Which TFs are expressed in Spemann’s organizer?

A

BMP high on ventral side

Spemann:

  • Chordin (later in dorsal mesoderm)
  • Noggin
  • Follistatin
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7
Q

How is the BMP gradient maintained?

A

Organizer expresses Chordin

-> Chordin forms tertiary complex with Twisted gastrulation gene and BMP dimer

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8
Q

BMP gradient patterns all 3 germ layers along DV axis.

Which structures develop in regions where its concentration is low?

A

low = dorsal

ecto: neural tube
meso: notochord
endo: pharynx

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9
Q

BMP gradient patterns all 3 germ layers along DV axis.

Which structures develop in regions where its concentration is high?

A

high = ventral

ecto: epidermis
meso: heart, blood
endo: intestine

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10
Q

Which 2 things specify AP axis?

A
  1. timing (anterior = early)
  2. position:
    - Wnt expressed in organizer when the latter is formed, later spreads out ventrally
    - Wnt is inhibited anteriorly in the head (Frizzled, Dickkopf, Cerebrus)
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11
Q

What (regarding the morphogen gradients) do all bilaterians have in common and what all vertebrates?

A

bilaterians: perpendicular Wnt and BMP
vertebrates: Wnt and BMP dependent on Nodal (high in D)

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12
Q

What is the correlation between Wnt and BMP signaling?

A

If Wnt is present: Dsh is active

  • inhibits Gsk3 = B-catenin is free = can localize to nucleus
  • Smad1 is stabilized = promotes BMP signaling
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13
Q

What is different about establishing the axes in amniotes?

A

Role of extra-embryonic tissues:

  • primitive streak is positioned by ANTERIOR VISCERAL ENDODERM (away from extraembryonic VE; low Nodal)
    • Wnt and Nodal inhibitors in rostral parts to inhibit caudal fate
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