Genomic Control Processes in Adult Body Part Formation

Bilaterian body parts are formed during development according to a common scheme. The basic principles, which apply irrespective of body part or organism, emerge from studies that reveal the genomically encoded mechanisms underlying body part formation. Here we consider partial gene regulatory networks (GRNs) that have been solved for a diverse variety of body parts including brains, hearts, limbs, and guts, in Drosophila and/or vertebrates. In all of these cases, the process of body part formation begins with the allocation of a progenitor field, defined by installation of an initial regulatory state, and its placement in respect to the axes of the body plan. There follows the progressively finer subdivision of this field into appropriately positioned regulatory state domains that generate the subparts and ultimately the cell types of the body part. Circuitry commonly encountered in these GRNs controls signaling interactions, exclusion functions and boundary formation, and often involves feedback and feed-forward regulation.