Coexpression and function of TERM -1 and fasciclin II during axonal outgrowth of identified brain interneurons in the grasshopper

During nervous system development in insects, several cell surface-associated molecules have been identified as candidates for guidance molecules involved in mediating correct axonal pathway recognition. Here we focus on a pair of identified brain interneurons in the grasshopper embryo, and use immunocytochemical methods to show that they coexpress two guidance molecules during axonal outgrowth. These molecules are TERM-1, a neuron-specific glycoprotein that is expressed exclusively by two brain interneurons, and fasciclin II, a pathway-specific glycoprotein that is expressed on fasciculating subsets of axons. We then did immunological blocking experiments in vivo under embryo culture conditions, and showed that both TERM-1 and fasciclin II are important for correct axonal guidance. These studies confirm the existence of functional molecular labels on defined axon pathways, and demonstrate the importance for correct axonal guidance of highly specific molecular labels that are expressed by individual identified neurons.