Membrane excitability in cleavage-arrested, differentiated cells

A rare glimpse of patterns of cell determination in the early embryo is provided by a recent article in the Journal of Physiology, in which T. Hirano and colleagues2 report that in. cleavage-arrested ascidian embryos, left the equivalent time to hatching, identified blastomeres differentiate to produce daughter cells with one of four well-defined types of membrane excitability; neural, epidermal, muscular or non-excitable. This interesting system contributes to our understanding of mosaicism and regulation in early development, and may enable detailed study of the development of membrane excitability.