part of regionalization midbrain-hindbrain boundary initiation MHB biosynthesis isthmus formation midbrain-hindbrain boundary biosynthesis GO:0021547 MHB formation midbrain-hindbrain boundary formation biological_process isthmus biosynthesis The regionalization process that gives rise to the midbrain-hindbrain boundary. The midbrain-hindbrain domain of the embryonic brain is comprised of the mesencephalic vesicle and the first rhombencephalic vesicle at early somitogenesis stages. An organizing center at the boundary patterns the midbrain and hindbrain primordia of the neural plate. neural plate anterior/posterior regionalization midbrain-hindbrain boundary development formation of anatomical boundary