vertebrate embryonic patterning 6

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Vertebrate Embryonic Patterning 6 Limb Formation

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Page 1: Vertebrate embryonic patterning 6

Vertebrate Embryonic Patterning 6

Limb Formation

Page 2: Vertebrate embryonic patterning 6

Tetrapod Limbanterior

posterior

proximal distal

ventral

dorsal

Page 3: Vertebrate embryonic patterning 6

Limb Bud Formation

Page 4: Vertebrate embryonic patterning 6

Establishment of Limb Fields

Page 5: Vertebrate embryonic patterning 6

Hox Gene Expression in Trunk During Limb Bud Development

Fig 23.21 Analysis of Biological Development 2nd ed, Kalthoff

Page 6: Vertebrate embryonic patterning 6

FGF10 Induces FGF8

supernumerary limbs from implanting FGF10 beads

Page 7: Vertebrate embryonic patterning 6

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

Page 8: Vertebrate embryonic patterning 6

Forelimb vs Hindlimb

Page 9: Vertebrate embryonic patterning 6

Forelimb vs Hindlimb

Correlates with Tbx5 & Tbx4

Expression Respectively

Tbx5

Tbx4

Page 10: Vertebrate embryonic patterning 6

Tbx4 Gain of Function Study

Tbx4 expressing retrovirus infected embryo

Page 11: Vertebrate embryonic patterning 6

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

Page 12: Vertebrate embryonic patterning 6

AER – Apical Ectodermal Ridge

Page 13: Vertebrate embryonic patterning 6

AER Necessary for Limb Bud Outgrowth

Removal of AER at various times prematurely truncates limb

Page 14: Vertebrate embryonic patterning 6

Reimplantation of older AER into younger bud causes loss of proximal structures

AER Necessary for Limb Bud Outgrowth

Reimplantation of younger AER into older bud causes duplication of distal structures

Page 15: Vertebrate embryonic patterning 6

Interactions of AER and PZ

Page 16: Vertebrate embryonic patterning 6

FGF8 in the AER

FGF in ectoderm AER3 day embryo

limb buds

Page 17: Vertebrate embryonic patterning 6

Hox Code of the Limb

Proximal Distal

Hoxa & d = forelimb; Hoxc & d = hindlimb

Page 18: Vertebrate embryonic patterning 6

Mammalian Hox Genes

Page 19: Vertebrate embryonic patterning 6

Hox Genes Required for Proper Limb Development

Hoxa-11/Hoxd-11 double knockout

wild-type

human with synpolydactyly resulting from homozygous

HOXD-13 null mutation

Page 20: Vertebrate embryonic patterning 6

Proximal-Distal Structures

Page 21: Vertebrate embryonic patterning 6

Anterior-Posterior Limb Axis

Zone of Polarizing Activity

ZPA

Page 22: Vertebrate embryonic patterning 6

Classic Experiments: Retinoic Acid Induced Limb Duplication

• Implanting RA soaked beads caused duplication of zeugopod/autopod structures

• Depletion of RA reduces the normal structures

Page 23: Vertebrate embryonic patterning 6

Shh is Expressed in ZPA

Page 24: Vertebrate embryonic patterning 6

Demonstration that Sonic Hedgehog is Primary ZPA Component

Page 25: Vertebrate embryonic patterning 6

Dorsal-Ventral Gene Patterning in Limb Bud

Fig 23.23 Analysis of Biological Development 2nd ed, Kalthoff

Page 26: Vertebrate embryonic patterning 6

Dorsal-Ventral Limb Axis

Lmx

1. Fgf-8 induces Shh2. Shh & Fgf-8 induce Fgf-43. All these induce Lmx-14. Wnt-7a in the ectoderm

represses Lmx-1 and induces Shh

BMPs

Page 27: Vertebrate embryonic patterning 6

Molecular Interactions in Limb Bud

Page 28: Vertebrate embryonic patterning 6

Dorsal-to-Ventral Transformations

WT mouse autopod

Wnt7a-/- mouse autopod

Page 29: Vertebrate embryonic patterning 6

Homology of Process: A-P Axis

Page 30: Vertebrate embryonic patterning 6

Homology of Process: D-V