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5-6-13_limbs_pt_1 - Unit 21 Limb Development Human Limb...

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Unit 21: Limb Development
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from A Child Is Born Human Limb Development
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Ventral Dorsal adapted from Gilbert 9e, Fig. 13.1 The limb bud has three axes Proximal distal axis = shoulder to finder tip axis Anterior-posterior axis = thumb-to little finger axis Dorsal-ventral axis = back of the hand to palm axis
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The limb bud forms from surface ectoderm and mesodermal mesenchyme Gilbert 9e, Fig. 13.3 The limb bud mesenchyme comes from lateral plate mesoderm. It is covered by surface ectoderm that differentiates differently from other epidermis.
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The limb bud forms due to the action of FGF10 and FGF8 simplified from Gilbert 9e, Fig. 13.20 FGF10 is expressed by mesoderm in the flank where limb buds will form. This leads to expression of FGF8 in the overlying limb bud ectoderm.
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FGF10 can induce an extra limb Gilbert 9e, Fig. 13.5 A bead soaked with FGF10 implanted in the flank is sufficient for an extra limb to grow out.
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FGF10 KOs lack limbs Min et al (1998). Genes & Dev . 12 :3156 FGF10 KO mice lack limb buds. Conclusion : FGF10 is sufficient and necessary for limb bud outgrowth.
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Limb bud ectoderm expresses FGF8 Gilbert 9e, Fig. 13.10 FGF8 is expressed in the overlying limb bud ectoderm. Other FGFs are also expressed there and are likely functionally redundant with FGF8, including FGF2 and FGF4, depending on the species.
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Limb bud ectoderm expresses FGF8 throughout its extension Gilbert 9e, Fig. 13.10 FGFs are expressed in specialized ectoderm throughout its proximal-distal outgrowth. FGFs act as a mitogen (stimulating proliferation) of underlying mesenchyme.
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Gilbert 9e, Fig. 13.7 The anterior-posterior position of
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