Axes specification Flashcards
What is the essential difference between basics of axis specification between anamniotes and amniotes?
anamniotes: contribution of maternal determinants
amniotes: interplay between embryonic and extraembryonic tissues
In xenopus: how does the organizer arise (what predetermines where the future dorsal site will form)?
- oocyte polarization along animal-vegetal axis (localization of maternal determinants)
- sperm entry site defines microtubule polymerization
- maternal determinants are transported along these microtubules to the future dorsal site
- B-catenin on dorsal site
- > high Nodal(-related) protein
- > low BMP at the site of organizer; high Chordin, Noggin, Folistatin
What do cells of the dorsal blastopore lip become?
Which characteristic transcription factor is present there?
DBL -> dorsal mesoderm
Chordin
What are the major functions of the organizer?
- initiation of the gastrulation movements
- generation of a self-regulation morphogen along DV
- dorsalisation
What is dorsalisation?
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
On which site along DV axis is BMP high?
Which TFs are expressed in Spemann’s organizer?
BMP high on ventral side
Spemann:
- Chordin (later in dorsal mesoderm)
- Noggin
- Follistatin
How is the BMP gradient maintained?
Organizer expresses Chordin
-> Chordin forms tertiary complex with Twisted gastrulation gene and BMP dimer
BMP gradient patterns all 3 germ layers along DV axis.
Which structures develop in regions where its concentration is low?
low = dorsal
ecto: neural tube
meso: notochord
endo: pharynx
BMP gradient patterns all 3 germ layers along DV axis.
Which structures develop in regions where its concentration is high?
high = ventral
ecto: epidermis
meso: heart, blood
endo: intestine
Which 2 things specify AP axis?
- timing (anterior = early)
- position:
- Wnt expressed in organizer when the latter is formed, later spreads out ventrally
- Wnt is inhibited anteriorly in the head (Frizzled, Dickkopf, Cerebrus)
What (regarding the morphogen gradients) do all bilaterians have in common and what all vertebrates?
bilaterians: perpendicular Wnt and BMP
vertebrates: Wnt and BMP dependent on Nodal (high in D)
What is the correlation between Wnt and BMP signaling?
If Wnt is present: Dsh is active
- inhibits Gsk3 = B-catenin is free = can localize to nucleus
- Smad1 is stabilized = promotes BMP signaling
What is different about establishing the axes in amniotes?
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