Lecture 16 Notes

Lecture 16 Notes - Vandan Desai BIOL 442Developmental...

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Vandan Desai BIOL 442—Developmental Biology 1 Lecture #16—Limb Formation in Vertebrates I. Vertebrate Limb Axes :: II. Mesodermal Derivatives :: A. Mesoderm involutes during gastrulation ; undersurface of embryo that leads to formation of many cell types : B. Paraxial mesoderm => muscle and bone C. Lateral plate mesoderm => lot of cells populate limbs III. Limb Bud Formation, Specification of Limb Types, and Growth :: A. Limb Bud Formation— i. Vertebrate limbs develop relatively late during embryogenesis ii. Limbs form in discrete regions along the body axis called limb fields In figure below, peribrachial flank tissue, free limb, and shoulder girdle have potential to give rise to limb, but only free limb gives rise to the limb structures ü The other two are associated w/ limbs, but don’t give rise to the limbs themselves Axes: Proximal-distal = shoulder- fingertip; hip-toe Anterior-posterior = thumb-pinky Dorsal-ventral = knuckles-palm
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Vandan Desai BIOL 442—Developmental Biology 2 ü If central area lost , cells from surrounding region can populate the limb fields (thus, all three have potential ) iii. Limb fields give rise to limb buds Limb bud forms from proliferating mesenchymal cells ( red dots ) originating in the lateral plate mesoderm and somites ü These cells underlie ectodermal tissue, creating a circular bulge called the limb bud iv. Lateral plate mesodermal cells give rise to skeletal elements of limb v. Somitic cells give rise to limb musculature B. FGF and Wnt Proteins Are Required for Limb Bud Formation along A-P Axis— i. Signal for limb bud formation comes from lateral plate mesoderm (b/w surface ectoderm and somatic mesoderm) that will form the limb mesenchyme ii. Limb mesenchyme secretes FGF10 (paracrine signal), initially throughout the lateral plate mesoderm and is unstable (won’t stay there): Wnt8c proteins stabilize FGF10 expression to the area where the hindlimb will form (posterior region) Wnt2b proteins stabilize FGF10 synthesis to the area where the forelimb will form (anterior region) Everywhere else FGF10 expression is lost
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Vandan Desai BIOL 442—Developmental Biology 3 C. Experimental Evidence for the Role of FGF10— i. Application of FGF soaked beads to lateral plate mesoderm between the prospective wings and legs of chicken embryos, results in formation of additional limbs FGF10 is therefore sufficient for the initiation of limb development: ü FGF10 can induce either ectopic wings or ectopic legs, depending on the position where it is applied FGF10 is also necessary/required for the initiation of limb development (have to get rid of it & see what happens in its absence): ü Transgenic mice lacking FGF10 have no forelimbs/hindlimbs ii. Necessary vs. Sufficient: You identified a novel organizer signal (Factor X) that when ectopically expressed in the ventral ectoderm causes an expansion of the neural domain. However, if you knock down the gene encoding this factor, neural tissue still forms normally. You conclude that?
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This note was uploaded on 12/09/2010 for the course BIOL 442 taught by Professor Brewster,r during the Spring '08 term at UMBC.

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Lecture 16 Notes - Vandan Desai BIOL 442Developmental...

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