principles to retain (class 4)

antagonism protects a territory

• example: DKK1 and NOGGIN reduce posteriorizing WNT and BMP activity

• developmental consequence: forebrain identity and emerge

mutual repression sharpens a border

• example: OTX2 opposes GBX2 at the isthmus

• developmental consequence: a stable organizer forms ta the midbrain hindbrain junction

a signal has context-dependent effects

• example: FGF acts during caudalization isthmic patterning and cortical arealization

• developmental consequence: timing location and competence determine the response

boundaries have mechanical properties

• example: reduced cell mixing and altered actomyosin tension occur at interfaces

• developmental consequence: molecular borders become visible constrictions

graded cues become combinatorial codes

• example: retinoic acid contributes to nested Hox expression

• developmental consequence: rhombomeres acquire distinct identities

early maps are refined later

• example: thalamocortical input acts on a cortical protomap

• developmental consequence: mature areas reflect intrinsic and activity-dependent mechanisms