 "Irx1", which is analogous to "IRX3" in birds and mammals, is expressed posterior to the ZLI.Studies have suggested that while "OTX2" positively restricts the ZLI anteriorly ("Shh" cannot be expressed where "OTX2" is not), 'IRX1" negatively restricts the ZLI posteriorly.Other genes crucial for differentiation in the brain, including Fgf genes responsible for patterning of the midbrain-hindbrain boundary (MHB), have been implicated in positioning of the ZLI.