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#joint formation

2 public questions tagged with this topic.

Limb Development -lll

Which factor is essential for joint formation in limbs?

Joint formation requires interruption of continuous chondrogenesis to create interzones with distinct fate. Cells at future joint sites downregulate Sox9 and collagen II, express Wnt14 Wnt4, GDF5 and increase hyaluronan production to prevent differentiation and promote cavitation and synovium formation. GDF5, also called cartilage-derived morphogenetic protein-1, a BMP family ligand, promotes joint specification, maintains interzone integrity, and recruits surrounding cells to form articular cartilage. Mutations in GDF5 cause brachydactyly type C and joint fusions. BMP4 promotes cartilage and apoptosis, SHH patterns AP, FGF8 drives proliferation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 20: GDF5 in joint formation and interzone.

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Tetrapod

Which molecule is required for joint formation in developing limbs?

Synovial joint formation requires segmentation of continuous chondrogenic condensation into separate skeletal elements. GDF5, also called Cartilage-Derived Morphogenetic Protein-1 belonging to BMP superfamily, expressed in interzone region marks future joint stripe. It maintains joint progenitors expressing Wnt14, Wnt9a, activates beta-catenin, inhibits cartilage maturation locally, induces expression of joint markers like suppression of Collagen type II. Mutations cause brachydactyly type C, symphalangism, joint fusions in humans. Exogenous GDF5 induces ectopic joints in developing limbs, while Noggin removal perturbs pattern, establishing GDF5 as essential factor initiating joint cavitation and boundaries.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: GDF5 and joint formation in limb interzone.

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