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#mesenchyme

3 public questions tagged with this topic.

Induction Morphogen -ll

What is the primary function of the mesenchyme in epithelial-mesenchymal interactions?

Mesenchyme synthesizes inductive cues that instruct overlying epithelium during organogenesis of lung, kidney, tooth and gland. Classical tissue recombination shows mammary mesenchyme converts salivary epithelium to mammary-like branching with milk protein expression, while dermal mesenchyme directs epidermal appendage fate such as hair versus feather. Secreted FGFs, TGF-beta, Wnt antagonists and matrix metalloproteinases remodeling basement membrane instruct proliferation, invagination and cytodifferentiation programs. Mechanical support and barrier functions are secondary; apoptotic removal is not its instructive role. Thus mesenchyme provides regional positional cues that determine shape, pattern and functional differentiation of epithelial organs.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Mesenchymal Instruction of Epithelial Morphogenesis.

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Limb Development -lll

Which experiment showed that mesenchyme determines limb identity?

Classic cross-species grafts proved mesenchymal instructive capacity for limb type. When wing lateral plate mesenchyme was transplanted beneath leg AER ectoderm, the resulting limb formed wing structures with feathers despite leg ectoderm, while leg mesenchyme under wing AER formed scales, claws and leg morphology. This showed AER is permissive and functionally equivalent along body axis, while underlying mesoderm contains instructive codes such as Tbx5 versus Tbx4 and Pitx1 defining forelimb versus hindlimb identity. Wnt7a or Lmx1b manipulations affect dorsoventral fate, Hox knockouts affect proximal-distal pattern but not whole limb identity determination.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: Mesenchyme determines limb-type identity transplantation.

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Tetrapod

Which experiment showed that mesenchyme determines limb identity?

Evidence that mesenchyme determines limb-type identity derives from classic transplantation where leg mesenchyme was placed beneath wing AER in chick embryos. Despite being covered by wing ectoderm providing only generic FGF8 outgrowth signals, resulting appendage formed leg structures including toes, claws, scales, demonstrating instructive information resides in mesoderm expressing Pitx1, Tbx4 versus Tbx5. Reciprocal experiment produced wing. This separates permissive epithelial signal from instructive mesenchymal program and establishes lateral plate mesoderm as source of limb-type specific pattern, maintained throughout development and regeneration experiments.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Mesenchyme determines limb identity transplantation experiments.

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