It has been identified in many bilaterians, including the arthropods, vertebrates, echinoderms, molluscs, nematodes, brachiopods, and polychaetes.
[4] engrailed plays a number of crucial roles in brain development across many species, including the determination of the hindbrain/midbrain border and aiding in neuronal axon guidance.
[4] In the model organism, Drosophila melanogaster, engrailed acts as a segment polarity gene in early embryonic development.
[7] engrailed homologs have also been found in many other arthropod species, including grasshoppers, milkweed bugs, centipedes, and beetles.
[4] Although it is not necessary for mineralization to occur, molluscs use engrailed to mark the boundaries of shell-forming fields (this has been demonstrated in cuttlefish,[6] gastropods,[8][9] bivalves,[4] polyplacophora,[4] and scaphopods)[10] but it has also been co-opted by the cephalopods in the production of evolutionary novelties such as the tentacles, eyes and funnel.