NEURAL EXPRESSION OF A SODIUM-CHANNEL GENE REQUIRES CELL-SPECIFIC INTERACTIONS

In the protochordate Halocynthia roretzi, voltage-activated sodium cur rent undergoes a change in kinetics within 48 hr of fertilization. Mol ecular cloning and microinjection of antisense DNA into single cells s uggest that the kinetic changes are due to the increased expression of a putative neural-specific sodium channel gene, TuNa I. TuNa I gene t ranscription is first induced in late stage gastrulae, preceding the a ppearance of the rapidly inactivating sodium current unique to neural cells. In cleavage-arrested and intact embryos, cell interactions betw een specific animal and vegetal blastomeres are required for induction of TuNa I gene expression. Our results implicate cell contact, prior to neurulation, as a mechanism for selectively activating the TuNa I g ene expressed in cells of the neural lineage.