Cellular 'neoteny': a possible developmental basis for chromaffin cell plasticity.

Adrenal medullary chromaffin cells, SIF cells and sympathetic neurons are derived from the sympatho-adrenal sublineage of the neural crest, and represent a range of cellular phenotypes extending from endocrine to neuronal. It is suggested here that these cell types may represent different stages of developmental 'arrest' along a linear pathway whose endpoint is a cholinergic sympathetic neuron. This model explains the 'transdifferentiation' of mature cells seen in this system as simply a delayed realization of transitions that normally occur between these stages during development. Such a 'linear model' of phenotypic diversification may be applicable to other developing systems that generate closely related but distinct cell types.