Nerve independent limb induction in axolotls.

Area of Science:

• Developmental Biology
• Regenerative Medicine
• Amphibian Biology

Background:

• Urodele amphibians possess remarkable limb regeneration capabilities.
• Limb regeneration involves endogenous reprogramming of dermal fibroblasts into multipotent blastema cells.
• Nerve presence is traditionally considered essential for initiating limb regeneration.

Purpose of the Study:

• To investigate the role of Growth and differentiation factor-5 (Gdf5) and Fibroblast growth factors (Fgfs) in amphibian limb regeneration.
• To determine if these signaling pathways can substitute for nerve-induced regeneration.
• To explore the potential of these factors in inducing cartilage differentiation in dermal fibroblasts.

Main Methods:

• Utilized the accessory limb model (ALM) to study limb regeneration.
• Applied Gdf5 to wounded skin in the absence of nerve supply.
• Investigated the effects of combined Gdf5 and Fgf applications on blastema formation and cartilage differentiation.
• Conducted in vivo and in vitro assays to assess cartilage formation potential of dermal fibroblasts.

Main Results:

• Gdf5 application alone initiated blastema-like structure formation without nerves, but with defects (e.g., absent Prrx1 expression).
• Co-application of Gdf5 and Fgfs (Fgf2, Fgf8) rescued these defects and induced limb formation without nerve supply.
• Dermal fibroblasts treated with Fgfs showed enhanced cartilage differentiation potential compared to those treated with Gdf5 alone.

Conclusions:

• Gdf5 and Fgfs signaling pathways are sufficient to substitute for nerve function in initiating amphibian limb regeneration.
• These factors play crucial roles in blastema formation and directing cell differentiation during regeneration.
• Understanding these molecular mechanisms provides insights into the early stages of limb regeneration.