HETEROTOPIC TRANSPLANTATION OF PRESUMPTIVE PLACODAL ECTODERM CHANGES THE FATE OF SENSORY NEURON PRECURSORS

The placode-derived cranial sensory neurons of the vestibular and nodo se ganglia in avian embryos exhibit differences in neurite growth rate and the duration of neurotrophin-independent survival in vitro that a rise prior to gangliogenesis and target contact (Davies, A. M. (1989) Nature 337, 553-555; Vogel, K. S. and Davies, A. M. (1991) Neuron 7, 8 19-830). To ascertain the state of commitment of presumptive placodal ectoderm to differentiate into neurons of the vestibular or nodose typ e, we performed heterotopic transplantation of labelled presumptive pl acodal ectoderm at E1.5 in the chicken embryo. We then assayed transpl ant-derived neurons for hindbrain innervation patterns, neurite growth and survival at E3.5. We show that presumptive placodal ectoderm is n ot determined to give rise to neurons of the vestibular or nodose phen otype at E1.5. Explantation of presumptive placodal ectoderm at E1.5 s howed that this ectoderm is also not specified to differentiate into n eurons at this stage. In addition, we demonstrate that non-neurogenic ectoderm from the trunk can give rise to nodose-type neurons when tran splanted heterotopically to the nodose region.