ahahahahahahaha… I bet you thought this was going to be interesting.
Tough. It's not. Anyway heres a diagram of how the diffusable limb bud morphogen Sonic Hedgehog (Shh) interacts with other proteins in the Zone of Polarising Activity and Apical Ectodermal Ridge during the determination and development of the antero-posterior axis in vertebrate limbs.
You're welcome to use this diagram except that it's quite awful looking really so I wouldn't recommend it.