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#limb blastema

2 public questions tagged with this topic.

Regeneration -lll

High levels of retinoic acid will convert a distal limb blastema to:

High levels of retinoic acid convert normally distal blastema fate to proximal by transcriptional reprogramming. RA via RAR-RXR binds enhancers of Meis1, Meis2, proximal Hox genes and upregulates glycosylated Prod1 isoform characteristic of proximal cells, while downregulating distal markers HoxA13. Consequently distal amputation plane that would regenerate only hand now regenerates complete arm including stylopod and zeugopod, producing proximalized duplicated limb. Dose-response experiments demonstrate progression: moderate RA duplicates forearm, high duplicates entire arm. This proximalizing effect underlies complete limb regeneration from distal blastema after exogenous retinoid exposure.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: High RA converting distal blastema to proximal structures.

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Tetrapod

What happens when a wrist blastema from a recently cut Axolotl forelimb is placed on a host hindlimb at the thigh level?

Blastema retains intrinsic positional memory encoded by differential expression of surface proteins Prod1, Meis1/2, and Hox codes resisting environmental reprogramming. When distal wrist blastema from axolotl forelimb is grafted onto proximal thigh of host hindlimb, despite richer nerve supply and growth factors, it does not intercalate to produce intervening arm segments. It regenerates only structures distal to its original level, producing wrist and hand. This demonstrates autonomous positional information stable through regeneration, principle that proximal cells can make distal but distal cannot make proximal without RA proximalization.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Positional memory and blastema transplantation experiments.

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