Left panel: Early developmental programs pattern single cells according to their position in the embryo. Morphogenic gradients establish specific homeodomain protein expression patterns along embryonic body axes (i.e. dorsal ventral axis = DV axis, anteroposterior axis = AP axis). Left middle panel: After neuroblasts have undergone several divisions, neurons terminally differentiate and establish unique identities depending on their homeodomain TF expression (color code). Right middle panel: A unique homeodomain TF expression specifies Ig domain receptor expression in matching synaptic partners, resulting in differential affinities of Ig domain proteins promoting selective synaptic target choice. Right panel: Common homeo-signatures regulate interaction partners within individual neuro-muscular circuits. 