Appropriate pattern formation following regulative regeneration in the hindbrain neural tube.

Patterns of neuronal differentiation and axon outgrowth were examined in regenerated neural tissue of the hindbrain of the chicken embryo. Specific regions of the hindbrain neural tube corresponding to identified rhombomeres were selectively removed unilaterally by microsurgery. Of the embryos that survived, about 35% exhibited regulative regeneration, wherein the missing hemi-rhombomere was reconstituted to normal size and morphology through compensatory proliferation and migration from adjacent tissue. The capacity for regeneration depended on the embryonic stage at which the ablation was performed and on whether the midline floor plate was included in the ablation. Ablations performed prior to the formation of morphologically overt rhombomere boundaries led to significantly lower frequencies of regulative regeneration than ablations performed after the formation of boundaries. Ablations that included the floor plate led to significantly lower frequencies of regulative regeneration than ablations sparing the floor plate. Regulative regeneration was also observed at low frequency following excision of an entire rhombomere. Within the regenerated hemi-rhombomere, identified neuron groups appeared in their normal positions and differentiated normal patterns of migration and axon outgrowth. The fidelity of this patterning, however, depended on the mediolateral position of the neuron group, being more reliable for neuron groups in the basal plate than in the alar plate. These results confirm the extensive regulative potential of the neural tube and demonstrate the capacity for appropriately patterned cellular differentiation within the regenerated tissue.