Question

Explain the the reciprocal induction mechanism between limb bud mesenchyme and epithelial cell

Answer 1

A reciprocal induction is the process which drives the mesenchyme to form an epithelium. It occurs in renal tubules and limb bud formation. In the process of limb growth, several interactions between the epithelial cells derived ectodermally and the mesenchyme of the lateral plate mesoderm resulting in reciprocal tissue interactions. Mesoderm cells along with themyotome migrate to the limb field and show accelarated growth until they cause the ectoderm above to bulge out called as limb bud. The formation of the organizer occur with fibroblast growth factor (FGF) at the the apical ectodermal ridge (AER) which is the end of the limb bud. It guides further development and controls cell death. But apoptosis is necessary to eliminate webbing between digits. Myotome is responsible for muscle components whereas the lateral plate cells produce the cartilaginous and skeletal portions of the limb. The AER also secretes FGF8 and FGF4 growth factors essential to induce proliferation in the mesoderm by maintaining the FGF10 signal. Wnt signalling regulate the position of FGF10 expression : Wnt8c in the hindlimb and Wnt2b in the forelimb. The position of the forelimb and the hindlimb are specified by two transcription factors: Tbx5 and Tbx4, respectively