A CRITICAL ROLE FOR THE SHH‐FGF LOOP DURING THE INITIATION OF LIMB REGENERATION

Abstract

Limb outgrowth is initiated and maintained by the secretion of FGFs in the apical ectodermal ridge (AER), and patterning regulated by SHH emanating from the posteriorly positioned zone of polarizing activity (ZPA). These factors are tightly linked during progressive limb formation by the SHH-FGF loop. Distal limb bud amputation (removing AER and ZPA) followed by application of FGF to the posterior (but not anterior) stump reactivates SHH expression and regeneration of the distal limb structures. We wondered whether SHH was sufficient to induce regenerative capacity and FGF-responsiveness in limb mesoderm. To determine the role of SHH in limb regeneration, we amputated developing wings (HH 23) and ectopically expressed SHH by confined microeclectroporation (CMEP) in the anterior and posterior stump margins in the presence or absence of FGF soaked beads. Also we ectopically expressed SHH in the anterior margin at HH 19 by CMEP, then applied FGF soaked beads to the anterior margin 24 h later (HH 23-24). Chic...