Simple early pattern from BMP gradient

Urbilateria theory
1. suggests the nervous system of all bilaterians develops through 2 waves of Chordin/BMP/Tolloid pathway signalling
Gastrulation
1. results in mesoderm and endoderm being on inside, and ectoderm (including future neural ectoderm/neurogenic ectoderm) being on outside
The Chordin/BMP network broadly dictates dorsal and ventral sides of the body.
1. Invertebrates have homologous genes to chordin/BMPs
  1. Different names
2. In vertebrates
  1. chordin-like gene is expressed on the dorsal side
3. In invertebrates
  1. chordin-like gene (Sog) is expressed on the ventral side
Neurulation
1. In vertebrates, dorsally-situated neural ectoderm undergoes neurulation, to form the neural tube, and the organiser undergoes convergent extension
  1. Results in shift in positions of  BMP and chordin
  2. IN both, the ‘patterning’ genes are induced by a BMP/dpp gradient that is established due to the antagonistic action of chordin/sog, and then to a series of repressive interactions
2. But note, relative common positions now of BMP and its antagonist in vertebrates and invertebrates AND homologous genes expressed within those
3. Crude patterning established that is conserved, and means there is conservation of CNS and PNS formation in Drosophila and vertebrates
  1. Make notes from slide 17
How do you get complexity in the vertebrate CNS?
1. Shh good candidate
  1. Evidence that it is a powerful morphogen
    1. Distribution
    2. Concentration-dependent effects on gene expression and cell fate (in vitro)
    3. Concentration-dependent effects on gene expression and cell fate (in vivo)
    4. Knock-out of receptor (ptc) or receptor-controlled ‘gate’ (smo) lead to alterations in cell fate at a distance

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Simple early pattern from BMP gradient

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	Created by Kristi Brogden about 11 years ago