Simple early pattern from BMP gradient

Simple early pattern from BMP gradient

1. Urbilateria theory

   • suggests the nervous system of all bilaterians develops through 2 waves of Chordin/BMP/Tolloid pathway signalling

2. Gastrulation

   • results in mesoderm and endoderm being on inside, and ectoderm (including future neural ectoderm/neurogenic ectoderm) being on outside

3. The Chordin/BMP network broadly dictates dorsal and ventral sides of the body.

   • Invertebrates have homologous genes to chordin/BMPs
     • Different names
   • In vertebrates
     • chordin-like gene is expressed on the dorsal side
   • In invertebrates
     • chordin-like gene (Sog) is expressed on the ventral side

4. Neurulation

   • In vertebrates, dorsally-situated neural ectoderm undergoes
neurulation, to form the neural tube, and the organiser undergoes convergent extension
     • Results in shift in positions of
 BMP and chordin
     • 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
   • But note, relative common positions now of BMP and its antagonist in vertebrates and invertebrates
AND homologous genes expressed within those
   • Crude patterning established that is conserved, and means there is conservation of CNS and PNS formation in Drosophila and vertebrates
     • Make notes from slide 17

5. How do you get complexity in the vertebrate CNS?

   • Shh good candidate
     • Evidence that it is a powerful morphogen
       • Distribution
       • Concentration-dependent effects on gene expression and cell fate (in vitro)
       • Concentration-dependent effects on gene expression and cell fate (in vivo)
       • Knock-out of receptor (ptc) or receptor-controlled ‘gate’ (smo) lead to alterations in cell fate at a distance

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