#blastema

Regeneration -l

Which process in regeneration involves the formation of a regeneration blastema?

Regeneration blastema denotes accumulation of undifferentiated proliferative cells at amputation plane beneath specialized wound epidermis. Its formation defines epimorphosis, regeneration involving considerable cell dedifferentiation, migration, and mitotic expansion prior to re-differentiation recapitulating developmental morphogenesis. Salamander limb blastema requires nerve signals and FGF from apical epidermal cap to sustain proliferation. Morphallaxis proceeds without visible blastema via repatterning existing tissues, compensatory regeneration expands remaining cells via hypertrophy and mitosis without blastema as liver, direct transdifferentiation converts differentiated cell type into another without intermediate blastema, such as lens regeneration from iris pigment epithelium.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Epimorphosis and regeneration blastema in salamander limb.

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Regeneration -lll

Blastema in epimorphosis primarily consists of:

Epimorphic blastema formed after amputation does not consist of pluripotent embryonic stem cells but of lineage-restricted yet multipotent progenitor cells derived via dedifferentiation of stump tissues. Muscle-derived blastema cells predominantly regenerate muscle, dermal fibroblasts generate cartilage and connective tissue, Schwann cells generate nerves, yet plasticity permits limited transdifferentiation under signals. Single-cell transcriptomics show blastema cells express progenitor markers Prrx1, Msx1, maintain positional memory via Meis, Hox gradients. Thus blastema comprises multipotent progenitor pool capable of producing multiple cell types needed for limb reconstruction while retaining memory of tissue origin and position.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Blastema composition as multipotent progenitors in epimorphosis.

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Regeneration -lll

What structure maintains positional information during limb regeneration in salamanders?

During salamander limb regeneration blastema itself carries and maintains positional information acquired from stump level. Cells retain memory through persistent expression of Meis1/2, HoxA9, HoxA13, and cell surface protein Prod1 gradient correlating with proximal-distal origin. Transplantation of proximal blastema to distal location results in intercalation, distal to proximal does not unless proximalized by RA. Blastema sorting assays demonstrate differential adhesion based on Prod1 levels preserving positional disparity. Therefore blastema constitutes repository of positional identity integrating retinoid and FGF cues ensuring regenerate restores correct pattern with faithful proximal-distal polarity.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Blastema maintains positional information via Prod1 and Meis.

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Regeneration -lll

Dedifferentiation to form a blastema is characteristic of:

Epimorphosis is regeneration type defined by formation of blastema mass through dedifferentiation of mature cells or mobilization of reserve progenitors forming proliferative growth zone that reconstructs lost structure. Unlike morphallaxis where existing tissue repatterned with minimal growth, epimorphosis involves extensive proliferation, histolysis of stump matrix, wound epidermis specialization. Examples include salamander limbs, zebrafish fins, lizard tails, requiring nerve trophic factors, FGF signaling, matrix metalloproteinases. Blastema later undergoes patterning and redifferentiation, restoring original architecture, thus representing growth-driven regeneration rather than remodeling or compensatory hypertrophy.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 21: Epimorphosis and blastema formation via dedifferentiation process.

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