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#proximal-distal axis

2 public questions tagged with this topic.

Limb Development -l

Which region of the limb bud is responsible for growth along the proximal-distal axis?

Growth along proximal-distal axis relies on progress zone, a highly mitotically active undifferentiated mesenchyme subjacent to apical ridge maintained by fibroblast growth factor 8 signaling. Cells residing longer in progress zone receive prolonged FGF exposure and adopt more distal fates: early exit yields stylopod humerus-femur, intermediate zeugopod radius-ulna-tibia-fibula, late retention autopod hand-foot. This progressive fate model explains sequential segment formation coordinated by Hox timing. Zone of polarizing activity patterns anterior-posterior axis, AER is signaling source, somites supply muscle progenitors for coordinated outgrowth.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Progress zone model and proximal-distal limb outgrowth timing.

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Regeneration -lll

Positional identity highest along proximal-distal axis is at:

Proximal-distal positional identity is graded with highest positional value at proximal base decreasing toward distal tip. Classical experiments measuring Prod1 concentration, Meis1/2 expression, and cell sorting affinities show proximal blastema cells possess highest adhesion and displace distal cells in mixed aggregates, reflecting maximal positional information. Retinoic acid concentration highest proximally reinforces this gradient. Consequently proximal cells can generate entire distal pattern via intercalation, while distal cells cannot generate proximal beyond origin unless proximalized by RA. Hence proximal base represents reference point of greatest positional value establishing polarity for regeneration and development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Positional identity highest at proximal base of limb.

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