Rapid induction of a hyperciliated phenotype in zinc-arrested sea urchin embryos by theophylline

Zinc ions, present since fertilization, will arrest embryos of the sea urchin Tripneustes gratilla at the hatched blastula stage, but such embryos lack long cilia, the usual characteristic of animalized embryos. Eventually these embryos will express a minimal long cilia phenotype, with a mean population < 1.4 times that of control blastulae, but only after contemporaneous control embryos gastrulate. Theophylline will rapidly but minimally animalize embryos when added after hatching, but its inductive ability decreases as the embryos gastrulate. Theophylline-animalized embryos produce cilia whose mean population length is > 1.5 times that of control blastulae. At any point from the time of hatching up until control complete gastrulation, theophylline added to zinc-arrested embryos will induce a hyperciliated phenotype with a mean population length nearly 3 times that of control blastulae. The elongation of cilia is immediate and significantly exceeds the rate of normal ciliary regeneration. Initially requiring the presence of theophylline, the hyperciliated phenotype becomes stable as control embryos begin gastrulation and, when deciliated, the induced embryos will regenerate hyperlong cilia in the absence of theophylline. The time dependence for both induction and phenotype stability would suggest that certain timing mechanisms are still operative in zinc-arrested embryos. This inducible system should facilitate studies of length control during ciliary elongation and regeneration.