Autonomous early differentiation of neurons and muscle cells in single cell cultures

The extent to which early differentiation of neurons and muscle cells is autonomous or governed by soluble factors released from other cells has been examined by following development of single cells plated alone in a simple, defined culture medium. The differentiation of electrical excitability and sensitivity to neurotransmitters of amphibian spinal neurons and trunk muscle in Xenopus embryos has already been described. For both cell types, differentiation in cultures containing relatively large numbers of dispersed cells parallels development in vivo, with respect to qualitative changes in membrane properties and the time course of development. Cell contacts are not required for this process. Here we show that the differentiation of membrane properties of single, isolated cells exhibits a similar set of changes, although muscle cells develop more slowly in some respects and all cells survive for a shorter period of time. The results suggest that the continued presence of specific extracellular differentiation-promoting factors is not required for these early steps of neuronal development, although a role for such factors in development of myocytes cannot be excluded. In contrast, survival factors secreted by other cells may be necessary to prolong the lifetimes of dissociated cells.