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Vertebrate Embryonic Patterning 6

Vertebrate Embryonic Patterning 6. Limb Formation. Tetrapod Limb. anterior. ventral. distal. proximal. dorsal. posterior. Limb Bud Formation. Establishment of Limb Fields. Hox Gene Expression in Trunk During Limb Bud Development.

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Vertebrate Embryonic Patterning 6

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  1. Vertebrate Embryonic Patterning 6 Limb Formation

  2. Tetrapod Limb anterior ventral distal proximal dorsal posterior

  3. Limb Bud Formation

  4. Establishment of Limb Fields

  5. Hox Gene Expression in Trunk During Limb Bud Development Fig 23.21 Analysis of Biological Development 2nd ed, Kalthoff

  6. FGF10 Induces FGF8 supernumerary limbs from implanting FGF10 beads

  7. Positioning of the Limb Field • Forelimb position lies near anterior expression boundary of hox b8, b9, c6, c9, & d9 • FGF8 expression in intermediate meso + hox genes induces FGF10 in the lateral plate meso • Wnts in the lateral plate maintain FGF expression in regions of hoxd9 expression • Between the fore & hindlimb buds, the developing kidney (mesonephros) inhibits FGF expression • Exogenous FGF can induce supernumerary limbs

  8. Forelimb vs Hindlimb

  9. Forelimb vs Hindlimb Correlates with Tbx5 & Tbx4 Expression Respectively Tbx5 Tbx4

  10. Tbx4 Gain of Function Study Tbx4 expressing retrovirus infected embryo

  11. Proximal Distal Limb Axis • AER • overlying ectoderm • responsible for maintaining outgrowth of limb • Progress zone • underlying mesoderm • region of cell division • maintained in active mitotic state by AER

  12. AER – Apical Ectodermal Ridge

  13. AER Necessary for Limb Bud Outgrowth Removal of AER at various times prematurely truncates limb

  14. AER Necessary for Limb Bud Outgrowth Reimplantation of younger AER into older bud causes duplication of distal structures Reimplantation of older AER into younger bud causes loss of proximal structures

  15. Interactions of AER and PZ

  16. FGF8 in the AER 3 day embryo limb buds FGF in ectoderm AER

  17. Hox Code of the Limb Proximal Distal Hoxa & d = forelimb; Hoxc & d = hindlimb

  18. Mammalian Hox Genes

  19. Hox Genes Required for Proper Limb Development wild-type Hoxa-11/Hoxd-11 double knockout human with synpolydactyly resulting from homozygous HOXD-13 null mutation

  20. Proximal-Distal Structures

  21. Anterior-Posterior Limb Axis Zone of Polarizing Activity ZPA

  22. Classic Experiments: Retinoic Acid Induced Limb Duplication • Implanting RA soaked beads caused duplication of zeugopod/autopod structures • Depletion of RA reduces the normal structures

  23. Shh is Expressed in ZPA

  24. Demonstration that Sonic Hedgehog is Primary ZPA Component

  25. Dorsal-Ventral Gene Patterning in Limb Bud Fig 23.23 Analysis of Biological Development 2nd ed, Kalthoff

  26. Dorsal-Ventral Limb Axis • Fgf-8 induces Shh • Shh & Fgf-8 induce Fgf-4 • All these induce Lmx-1 • Wnt-7a in the ectoderm represses Lmx-1 and induces Shh Lmx BMPs

  27. Molecular Interactions in Limb Bud

  28. Dorsal-to-Ventral Transformations WT mouse autopod Wnt7a-/- mouse autopod

  29. Homology of Process: A-P Axis

  30. Homology of Process: D-V

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